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Although the force-length properties of muscles have an approximately parabolic shape, in vivo not all the force-length curve is necessarily used, only a portion of the curve is expressed (i.e., ascending, plateau, or descending regions of the force-length curve). The number of sarcomeres in series in a muscle fiber affects the expressed section of the force-length curve; this number can be influenced by the nature of activity the muscle experiences. It was hypothesized that the reduced range of motion ice skaters experience, because of the constraints imposed by the ice skates, that the gastrocnemii of a group of ice skaters will adapt and will more frequently express in vivo the plateau of the force-length curve compared with a nonspecifically trained population. Twelve NCAA Division I female ice hockey players volunteered for the study. Their maximum isometric ankle plantarflexion moments were recorded for 6 ankle angles and 3 knee angles. Exploiting the biarticularity of the gastrocnemius, the expressed sections of the subject's force-length curves were determined. Six subjects operated over the ascending limb, 5 operated over the plateau region, and 1 over the descending limb. This frequency of distribution for ice hockey players was statistically different to the distribution measured for 28 nonspecifically trained subjects from a previous study (p < 0.0001). These results likely reflect morphological differences between the 2 groups for their gastrocnemii, potentially arising from the limited range of gastrocnemius length feasible in ice-skates. These results have implications for the specificity of their off-ice training for ice hockey players. [ABSTRACT FROM AUTHOR]

The squat is used to enhance performance and rehabilitate the lower body. However, muscle forces and how muscles accelerate the center of mass (CoM) are not well understood. The purpose was to determine how lower extremity muscles contribute to the vertical acceleration of the CoM when squatting to parallel using 85% one-repetition maximum. Thirteen female subjects performed squats in a randomized fashion. Musculoskeletal modeling was used to obtain muscle forces and muscle-induced accelerations. The vasti, soleus, and gluteus maximus generated the largest upward accelerations of the CoM, whereas the muscles that produced the largest downward acceleration about the CoM were the hamstrings, iliopsoas, adductors, and tibialis anterior. Our findings indicate that a muscle's function is task and posture specific. That is, muscle function depends on both joint position and how an individual is interacting with the environment. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine muscle-specific contributions to various types of vertical ground reaction force (vGRF) profiles in collegiate basketball players. Players from a men's (n = 5; height: 1.84 ± 0.14 m; mass: 92.8 ± 11.4 kg) and a women's (n = 5; 1.71 ± 0.09 m; mass: 80.1 ± 17.6 kg) basketball team completed 3-5 countermovement jumps (CMJ) while motion capture and force plate data were recorded. Muscle-specific contributions to vGRF were calculated through vGRF decomposition analysis. Profiles of vGRF were analyzed based on the presence of unimodal or bimodal peaks during the CMJ. The results showed that the soleus (SOL), gastrocnemii (GAS), vastii (VAS), and gluteus maximus (GMX) muscles all contributed to upward vGRF generation throughout the entire CMJ duration. The contributions were greatest for the SOL (1.78 body weight [BW]), intermediate for the GAS (0.96 BW) and VAS (0.72 BW), and negligible for the GMX (0.11 BW). For unimodal vGRF profiles, SOL contributions coincided with peak vGRF, whereas VAS contributions were stable throughout most of the CMJ. For bimodal vGRF profiles, SOL and VAS contributions explained the presence of the first vGRF peak, whereas GAS and VAS contributions explained the second vGRF peak. Differences between vGRF profiles appear to be the result of distinct force contributions from the VAS muscle, which may have implications for the analysis of vGRF time series data during CMJ testing. [ABSTRACT FROM AUTHOR]

The effectiveness of high-load and plyometric exercises as conditioning activity (CA) is not well described in the level of performance enhancement and muscle-tendon properties. Therefore, this study aimed to compare the effectiveness of high-loaded back squats and body mass tuck jumps among amateur soccer players on the height of countermovement jump performed without (CMJ) and with arm swing (CMJa) and to verify the usefulness of the myotonometry in assessing the level of CA-induced fatigue. Therefore, 16 male amateur soccer players (resistance training experience: 2 ± 1 year, relative 1 repetition maximum back squat strength: 1.41 ± 0.12 kg·body mass-1) performed 3 experimental sessions to compare the acute effects of 3 sets of 3 repetitions at 85% one repetition maximum of half back squats (HL), 3 sets of 5 repetitions of tuck jump exercises (PLY), and no CA (CTRL) on CMJ and CMJa height. Moreover, the gastrocnemius medialis and Achilles tendon tone and stiffness were examined. Measurements were performed 5 minutes before CA and in the third, sixth, and ninth minutes after CA. The CMJ height significantly increased from pre-CA to post-CA in the CTRL (p = 0.005; effect size [ES] = 0.36; Δ = +3.4%) and PLY (p = 0.001; ES = 0.83; Δ = +8.8%) conditions. Moreover, post-CA jump height was significantly higher in PLY than in the HL condition (p = 0.024; ES = 0.6; Δ = +5.9%). No significant differences were found for CMJa height, tone, and stiffness of gastrocnemius medialis and Achilles tendon. The low-volume plyometric CA (i.e., 3 sets of 5 repetitions) is recommended instead of high-loaded CA (=85% one repetition maximum) for amateur athletes. In addition, it has been established that the performance improvement was independent of changes in the mechanical properties of the gastrocnemius medialis and Achilles tendon. Furthermore, it seems that the complexity of the post-CA task may affect the magnitude of the postactivation performance enhancement. [ABSTRACT FROM AUTHOR]

Foam rolling (FR) is a practice that has increased in popularity before and after resistance training. The purpose of this study was to compare the acute effects of different foam rolling periods for the lower body muscles on subsequent performance, myoelectric activity and rating of perceived exertion in trained men. Fourteen men (26.2 ± 3.2 years, 178 ± 0.04 cm, 82.2 ± 10 kg and body mass index 25.9 ± 3.3kg/m-2) volunteered for this study. Four repetition maximum (4-RM) loads were determined for hexagonal bardeadlift and 45°- angled leg press during test and retest sessions over two nonconsecutive days. The experimental conditions included a traditional protocol (TP) with no prior foam rolling, and four other conditions that involved FR applied to the quadriceps, hamstrings and triceps surae for one set of 30 sec (P1), two sets of 30 sec (P2), three sets of 30 sec (P3), or four sets of 30 sec (P4).The resistance training consisted of five sets with 4-RM loads. The number of repetitions completed, the myoelectric activity of lower limbs were recorded, as well as the rating of perceived exertion for each protocol. There were no differences between the protocols in the total repetitions for the hexagonal bar deadlift and 45° angled leg press exercises. Similar results between protocols were also noted for muscle activity and rated perceived exertion (RPE). Therefore, the results of the present study indicated that the FR didn't provide effects on performance, myoelectric activity and rating of perceived exertion responses during high intensity resistance performance for lower limb exercises. [ABSTRACT FROM AUTHOR]

Hill, MW, Roberts, M, Price, MJ, and Kay, AD. Effects of flywheel training with eccentric overload on standing balance, mobility, physical function, muscle thickness, and muscle quality in older adults. J Strength Cond Res 36(11): 3190–3199, 2022—This study investigated the effects of a 6-week eccentric overload flywheel training program on vastus lateralis (VL) and gastrocnemius medialis (GM) muscle thickness and muscle quality (echo intensity), mobility (Timed Up and Go [TUG]), physical function (sit-to-stand), and balance (postural sway) performance. Nineteen subjects were assigned to either a flywheel training group (n = 11, age = 66.4 ± 5.2 years) or a control group (n = 8, age = 65.9 ± 3.8 years). The flywheel group underwent twice weekly squat and calf raise exercises for 6 weeks with outcome measures assessed before and after training or a time-matched control period. Throughout the training, subjects were instructed to contract as fast as possible with maximal effort during the concentric phase and to maximally resist the pull during the eccentric phase. The alpha value was a priori set at p < 0.05. Statistically significant (p < 0.05) mean (SD) increases in right and left VL (7.6–9.6 ± 7.7–9.8%) and GM (8.6–8.7 ± 6.4–11.5%) muscle thickness and a reduction in VL (10.2–11.3 ± 5.9–7.9%) and GM (11.7–11.9 ± 5.6–9.6%) echo intensity were accompanied by faster TUG time (13.7 ± 7.0%) improved sit-to-stand performance (17.8–23.5 ± 7.6 – 13.4%) and reduced postural sway (29.7–42.3 ± 13.2–24.2%) after 6 weeks of flywheel training. There were no differences in any outcome measures between the treatment and control group at baseline (p > 0.05). Overall, we observed substantial gains in muscle thickness and muscle quality, in addition to enhanced physical function, balance, and mobility performance among older adults after flywheel training, which may have important implications for preserving the functional capacity of older adults. [ABSTRACT FROM AUTHOR]

Matsuo, H, Kubota, M, Shimada, S, Kitade, I, Matsumura, M, Nonoyama, T, Koie, Y, Naruse, H, Takahashi, A, Oki, H, Kokubo, Y, and Matsumine, A. The effect of static stretching duration on muscle blood volume and oxygenation. J Strength Cond Res 36(2): 379–385, 2022—Muscle blood volume increases due to stretching; however, the minimum duration of stretching to sustainably increase the muscle blood volume after stretching has not yet been elucidated. This study examined whether the duration of static stretching influenced the muscle blood volume and oxygenation. Ten healthy male subjects participated in this controlled laboratory study. Static stretching of the gastrocnemius muscle was performed for 5 durations (20 seconds, and 1, 2, 5, and 10 minutes). Changes in both the total-Hb (ΔtHb), as an index of blood volume, and tissue oxygenation index (ΔTOI) from baseline were determined using near-infrared spectroscopy. Both the ΔtHb and ΔTOI decreased during stretching and increased after stretching. The minimum value of ΔtHb during stretching did not differ in each of the 5 durations, but minimum ΔTOI progressively decreased with longer durations of stretching. The peak value of ΔtHb after stretching increased with longer durations of stretching. The value of ΔtHb at 5 minutes after the end of stretching increased with more than 2 minutes of stretching compared with 20 seconds of stretching, although the value of ΔtHb did not significantly differ between the 2, 5, and 10 minutes' durations. These findings suggest that a longer duration of stretching elicits a decrease in muscle oxygenation during stretching, and an increase in both the muscle blood volume and oxygenation after stretching. The results indicated that the minimum duration of stretching to sustain an increase in the muscle blood volume after stretching is 2 minutes. [ABSTRACT FROM AUTHOR]

Kipp, K, Kim, H, and Wolf, WI. Muscle-specific contributions to lower extremity net joint moments while squatting with different external loads. J Strength Cond Res 36(2): 324–331, 2022—The purpose of this study was to determine muscle-specific contributions to lower extremity net joint moments (NJMs) during squats with different external loads. Nine healthy subjects performed sets of the back squat exercise with 0, 25, 50, and 75% of body mass as an added external load. Motion capture and force plate data were used to calculate NJMs and to estimate individual muscle forces via static optimization. Individual muscle forces were multiplied by their respective moment arms to calculate the resulting muscle-specific joint moment. Statistical parametric mapping (α = 0.05) was used to determine load-dependent changes in the time series data of NJMs and muscle-specific joint moments. Hip, knee, and ankle NJMs all increased across each load condition. The joint extension moments created by the gluteus maximus and hamstring muscles at the hip, by the vastii muscles at the knee, and by the soleus at the ankle all increased across most load conditions. Concomitantly, the flexion moment created by the hamstring muscles at the knee also increased across most load conditions. However, the ratio between joint moments created by the vastii and hamstring muscles at the knee did not change across load. Similarly, the ratio between joint moments created by the gluteus maximus and hamstring muscles at the hip did not change across load. Collectively, the results highlight how individual muscles contribute to NJMs, identify which muscles contribute to load-dependent increases in NJMs, and suggest that joint moment production among synergistic and antagonistic muscles remains constant as external load increases. [ABSTRACT FROM AUTHOR]

Chiu, LZF and Daehlin, TE. Midfoot and ankle mechanics in block and incline heel raise exercises. J Strength Cond Res 35(12): 3308-3314, 2021-Although the heel raise exercise is performed to strengthen the calf muscles, the combination of calf muscle and ground reaction forces elicits moments that may deform the foot's longitudinal arch. The primary purpose of this investigation was to examine whether the foot muscles contribute to supporting the longitudinal arch during heel raises. The secondary purpose was to compare foot and ankle mechanical efforts between traditional block vs. 22[degrees] incline heel raises. Six women and 6 men performed heel raises with body mass plus a barbell loaded with 40% (BM + 40%) and 60% (BM + 60%) of their body mass. Three-dimensional motion analysis and force platform data were collected. The midfoot joint was evaluated from the angle between the forefoot and rearfoot (i.e. arch angle) and net joint moment, which may elevate or reduce the arch height. Midfoot joint arch elevator moment seemed to be greater for BM + 60% than BM + 40% (p < 0.05; Cohen's d = 1.24-1.61), with minimal change in arch angle (p < 0.05; Cohen's d = 0.15-0.19). Midfoot joint arch elevator and ankle plantar flexor moments seemed to be greater in incline vs. block heel raises for both loads (p < 0.05; Cohen's d = 0.58-0.67). The increase in midfoot joint arch elevator moment with trivial change in arch angle supports the hypothesis that the foot muscles contribute to longitudinal arch support during heel raises. Performing incline heel raises may be hypothesized to be more effective to stimulate foot and calf muscle adaptations than block heel raises. [ABSTRACT FROM AUTHOR]

Marchetti, PH, Magalhaes, RA, Gomes, WA, da Silva, JJ, Stecyk, SD, and Whiting, WC. Different knee and ankle positions affect force and muscle activation during prone leg curl in trained subjects. J Strength Cond Res 35(12): 3322-3326, 2021-Different joint positions for biarticular muscles may affect force and muscular activity during single-joint exercises. The aim of this study was to compare the maximal isometric contractions and muscle activation in 2 different knee and ankle positions during prone leg curl exercise in trained subjects. Fifteen resistance-trained men (27 +/- 4 years, 178.80 +/- 5.72 cm, 86.87 +/- 12.51 kg) were recruited. The peak force (PF) and muscle activation of biceps femoris, gastrocnemius lateralis (GL), and soleus lateralis (SL) were measured during knee flexion at 0 and 90[degrees] and maximal dorsiflexion (D) or plantarflexion (P). Three maximal voluntary isometric contractions of 5 seconds were performed for each combination of knee and ankle positions. Two-way repeated-measures analysis of variances were used for all dependent variables. For PF, there was a significant difference between ankle positions (D x P) at 90[degrees] (p = 0.009) and knee positions (0 x 90[degrees]) for D (p < 0.001) and P (p < 0.001). Peak force was greater with the knee at 0[degrees] and the ankle maximally dorsiflexed. For GL, there was a significant difference between ankle (D x P) at 0[degrees] (p = 0.002) and knee positions (0 x 90[degrees]) for D (p = 0.005). Gastrocnemius lateralis activation was greater with the knee at 90[degrees] of flexion and the ankle maximally dorsiflexed. For SL, there was a significant difference between ankle positions (D x P): at 90[degrees] (p = 0.001) and at 0[degrees] (p = 0.002). Soleus lateralis is more active in plantarflexion irrespective of the knee joint position. Isometric contractions with full knee extension produce more strength regardless of the ankle position; neither the knee position nor the ankle position may influence the activity of the hamstrings. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the effects of active and passive warm-ups on flexibility and strength of calf muscles. Fourteen healthy males (age: 23.1 ± 2.6 years, height: 172.7 ± 5.6 cm, and body mass: 64.5 ± 7.0 kg) performed 3 types of warm-ups respectively for 10 minutes in a random order: an active warm-up by pedaling a cycling ergometer, an active warm-up doing repeated isometric contractions, and a passive warm-up in a hot water bath. To assess flexibility, range of motion (ROM) of ankle dorsiflexion, passive torque of ankle plantarflexion, and muscle tendon junction (MTJ) displacement were measured and then muscle tendon unit (MTU) stiffness was calculated. After the flexibility assessment, peak torque during maximum voluntary isometric contraction was measured to assess the isometric strength. These data were compared before and after each warm-up. As a result, all 3 types of warm-ups increased ROM (p < 0.05) and passive torque at terminal ROM (p < 0.01), but there were no significant changes in MTU stiffness or MTJ displacement. The active warm-up by pedaling a cycling ergometer increased peak torque during isometric contraction (p < 0.05), whereas the other warm-ups did not show significant alterations. In conclusion, the active warm-up with aerobic exercise increased flexibility and strength of the calf muscles. [ABSTRACT FROM AUTHOR]

This study investigated how a 6-second maximal voluntary isometric contraction (MVIC) conditioning affected plantar flexor twitch rate of torque development (RTDTW), as well as peak torque (PTCC) and rate of torque development (RTDCC) of maximal voluntary concentric contractions (MVCC) performed at 60°·s−1. RTDCC and normalized triceps surae electromyography signals (EMGTS) were measured during different phases of contraction. In addition, muscle tendon unit passive stiffness index (SI) calculated from the torque-angle relation was measured after each MVCC. Enhancements were found in the RTDTW immediately (by 59.7%) and up to 480 seconds (by 6.0%) after MVIC (p < 0.05). RTDCC during the 100–200 ms, 50–200 ms, and 0–200 ms phases and PTCC were enhanced (by 5.7–9.5%) from 90 to 300 seconds after conditioning (p < 0.05). Neuromuscular efficiency increased (decreased EMGTS/RTDCC) in the 50–200 ms and 0–200 ms phases by 8.8–12.4%, from 90 to 480 seconds after MVIC (p < 0.05). No significant changes were found in the SI or in RTDCC during the 50–100 ms phase, suggesting that the enhancements reported reflect mainly contractile rather than neural or tensile mechanisms. PAP effects on PTCC and RTDCC were significant and more durable at a lower velocity than previously reported. Enhancement in RTDCC and neuromuscular efficiency were found to be more prominent in later phases (>100 ms) of the MVCC. This suggests that enhanced contractile properties, attained through MVIC, benefit concentric contraction performance. [ABSTRACT FROM AUTHOR]

Duc, S, Rønnestad, BR, and Bertucci, W. Adding whole-body vibration to preconditioning squat exercise increases cycling sprint performance. J Strength Cond Res 34(5): 1354-1361, 2020-This study investigated the effect of performing a preconditioning exercise with or without whole-body vibration (WBV) on a subsequent cycling sprint performance. Fourteen trained subjects performed 2 separate test sessions in randomized order. After a warm-up, the preconditioning exercise (body-loaded halfsquats) was applied: 30 seconds of half-squats with WBV (40 Hz, 2 mm) or 30 seconds of half-squats without WBV with a 10-second all-out sprint performed after 1 minute. Surface electromyography (EMG) was measured from the vastus medialis, vastus lateralis, and gastrocnemius medialis during the sprints. Blood lactate level (BL), heart rate (HR), and rating of perceived exertion (RPE) were determined immediately after the 10-second sprint. Performing preconditioning exercise with WBV resulted in superior peak (1,693 6 356 vs. 1,637 6 349 W, p # 0.05) and mean power output (1,121 6 174 vs. 1,085 6 175 W, p # 0.05) compared with preconditioning exercise without WBV. Effect sizes showed a moderate and large practical effect of WBV vs. no WBV on peak and mean power output, respectively. No differences were observed between the conditions for BL, HR, and RPE after the sprints and in EMG activity during the sprints. In conclusion, it is plausible to suggest that body-loaded half-squats with WBV acutely induce higher power output levels. The practical application of the current study is that body-loaded squats with WBV can be incorporated into preparations for specific sprint training to improve the quality of the sprint training and also to improve sprint performance in relevant competitions [ABSTRACT FROM AUTHOR]

Scott, DJ, Ditroilo, M, and Marshall, P. Effect of accommodating resistance on the post-activation potentiation response in rugby league players. J Strength Cond Res 32(9): 2510–2520, 2018—This study examined the postactivation potentiation (PAP) response of 2 conditioning activities (CA), the hex bar deadlift and back squat, combined with accommodating resistance; this adds a percentage of the total resistance during the exercise. Twenty amateur rugby league players performed 2 experimental trials and a control trial without a CA. Participants performed a countermovement jump (CMJ) before and 30, 90, and 180 seconds after 1 set of 3 repetitions of each CA at 70% 1 repetition maximum (RM), with up to an additional 23% 1RM from accommodating resistance. Peak power output (PPO), force at PPO, velocity at PPO, and jump height were calculated for each CMJ. Surface electromyography (EMG) of the vastus lateralis (VL), rectus femoris (BF), tibialis anterior (TA), and gastrocnemius medialis (GM) was also measured. Repeated-measures analysis of variance revealed no significant (p > 0.05) PAP response for either exercise condition when comparing CMJ variables with baseline values nor were there any significant (p > 0.05) differences between exercise conditions. However, individualized recovery intervals (baseline vs. maximum potentiation response) demonstrated significant (p ≤ 0.05) improvements in PPO (3.99 ± 4.99%), force at PPO (4.87 ± 6.41%), velocity at PPO (4.30 ± 5.86%), jump height (8.45 ± 10.08%), VL EMG (20.37 ± 34.48%), BF EMG (22.67 ± 27.98%), TA EMG (21.96 ± 37.76%), and GM EMG (21.89 ± 19.65%). Results from this study must be interpreted with caution; however, it is conceivable that athletic performance can be acutely enhanced when complex training variables are individualized. [ABSTRACT FROM AUTHOR]

Masumoto, K, Mefferd, KC, Iyo, R, and Mercer, JA. Muscle activity and physiological responses during running in water and on dry land at submaximal and maximal efforts. J Strength Cond Res 32(7): 1960–1967, 2018—We investigated muscle activity, oxygen uptake, heart rate, and rating of perceived exertion during running in water and on dry land at submaximal and maximal efforts. Eleven recreational runners performed deep-water running (DWR) and treadmill running (TMR) graded exercise tests on separate days. On the third-test day, the subjects exercised at their 60, 80, and 100% of maximal oxygen uptake (V̇ o 2max) by matching specific stride frequencies or running speeds. V̇ o 2max, maximal heart rate (HRmax), and rating of perceived exertion at maximal effort (RPEmax) were measured. Furthermore, muscle activity from the rectus femoris, biceps femoris, tibialis anterior, and gastrocnemius were measured. V̇ o 2max (DWR: 48.9 ± 5.7 ml·kg−1·min−1; TMR: 59.2 ± 5.6 ml·kg−1·min−1; p < 0.001) and HRmax (DWR: 174.1 ± 9.6 beats·min−1; TMR: 191.2 ± 6.9 beats·min−1; p < 0.001) were each lower during DWR vs. TMR. In addition, RPEmax was not significantly different between DWR and TMR (DWR: 17.8 ± 1.9; TMR: 18.4 ± 1.3; p > 0.05). Furthermore, muscle activity from all tested muscles was not influenced by the interaction of mode and intensity (p > 0.05). Muscle activity from all tested muscles was different between modes (p < 0.05) and between intensities (p < 0.001). Specifically, muscle activity from the tested muscles during DWR was 29–69% lower than that of TMR at maximal effort. Athletes and coaches should consider that the exercise intensity during DWR can be overestimated, if exercise prescription was made according to the maximal responses during TMR. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of resistance training (RT) on heart rate variability (HRV) and on blood pressure (BP) responses to acute and short-term exposure in treated hypertensive (HT) subjects. Twenty-one men participated in the study, 8 HT under drug treatment regimen and achieving adequate BP control before inclusion and 13 normotensive (NT). The RT protocol consisted of 12 sessions with eight exercises (leg extension, leg press, leg curl, bench press, seated row, triceps push-down, seated calf flexion, and seated arm curl) performed for two sets of 15--20 repetitions with 50% of one repetition maximum with 2-minute rest intervals in between sets, 33/week. Heartbeat measurements were taken before and after RT, and BP was measured at the beginning and at the end of each session after 10-minute rest. The repeated measures analysis of variance (effect: group vs. training) evaluated BP and HRV responses. Effect size (ES) calculation measured the magnitude of the RT effect on these variables. There was a statistically significant reduction in postexercise systolic BP in both groups (p = 0.040), without significant change in resting BP along RT (p = 0.159). Regarding HRV, it was observed a reduced sympathetic-vagal balance (training interaction vs. group: p = 0.058, ES = 20.83) in HT subjects. Resistance training promotes a significant acute reduction of BP in the HT and NT groups and provides a slight benefit of cardiac autonomic balance in the HT. [ABSTRACT FROM AUTHOR]

Nordic walking (NW) has proven to be a simple and safe mode of exercise that can be used in various types of sport, recreation, and rehabilitation activities. The aim of this study was to assess the effect of Nordic walking and slope of the ground on lower limb muscle activity. The experimental group consisted of 22 healthy men (aged 22.8 ± 1.4 years). The subjects walked on a treadmill at a self-selected speed. Two walking conditions (NW and walking) and 2 ground slopes (level ground and uphill walking at an 8% incline) were used. The surface electromyographic signals of the gastrocnemius lateralis, tibialis anterior, vastus medialis, rectus femoris, biceps femoris and gluteus medius were recorded. Nordic walking resulted in increased activity of some lower limb muscles, particularly during the first half of the stance phase, and decreased muscle activity during the first half of the swing phase. Uphill walking elicited increased muscle activity compared with level walking, particularly during the stance phase and the second half of the swing phase during both walking and NW, and the change was more pronounced during walking. We concluded that NW increased muscle activity in the lower extremities compared with walking, particularly on level ground. Increasing the ground slope enhanced the muscle activity to a much greater extent than NW. [ABSTRACT FROM AUTHOR]

The purpose of this study was to assess the effects of abdominal drawing-in and Pilates breathing on the activity of lower limb muscles during squats. Adults (n = 13, 22 ± 3 years old) with some Pilates experience performed three 60° squats under each of the following conditions in a random order: (I) normal breathing, (II) drawing-in maneuver with normal breathing, and (III) drawing-in maneuver with Pilates breathing. Peak-normalized surface electromyography of the rectus femoris, biceps femoris, gastrocnemius medialis, and tibialis anterior during the knee flexion and extension phases of squat exercises was analyzed. There were significant differences among the conditions during the knee flexion phase for the rectus femoris (p = 0.001), biceps femoris (p = 0.038), and tibialis anterior (p = 0.001), with increasing activation from conditions I to III. For the gastrocnemius medialis, there were significant differences among the conditions during the knee extension phase (p = 0.023), with increased activity under condition I. The rectus and biceps femoris activity was higher during the extension vs. flexion phase under conditions I and II. The tibialis anterior activity was higher during the flexion compared with the extension phase under all conditions, and the medial gastrocnemius activity was higher during the extension phase under condition I. Doing squats with abdominal drawing-in and Pilates breathing resulted in increased rectus, biceps femoris, and tibialis anterior activity during the flexion phase, increasing movement stability during squat exercises. [ABSTRACT FROM AUTHOR]

This study examined the leg muscle activity during exposure to different whole-body vibration (WBV) intensities while performing various dynamic exercises in patients with chronic stroke. Thirty patients with chronic stroke performed a series of dynamic exercises under 3 conditions: (a) low-intensity WBV (peak acceleration: 0.96 units of gravity of Earth [g]), (b) high-intensity WBV (1.61 g), and (c) no WBV. Neuromuscular activation was recorded with surface electromyography (EMG) on bilateral biceps femoris (BF), vastus lateralis, tibialis anterior (TA), and gastrocnemius (GS) in both legs and was reported as EMGrms (root mean square) normalized to % maximal voluntary contraction. The EMG amplitude of all tested muscles was significantly increased by adding WBV during dynamic exercise (p ≤ 0.05). The EMG amplitude of BF, TA, and GS during exposure to high-intensity WBV was significantly greater than low-intensity WBV (p ≤ 0.05). The increase in EMG amplitude caused by WBV was exercise dependent in GS and TA (p ≤ 0.05). The EMG response to WBV in GS and BF in the affected leg was significantly greater than the corresponding muscles in the unaffected leg (p ≤ 0.05). The extent of WBV-induced muscle activity was dependent on the dynamic exercise, WBV intensity, and muscle trained among patients with chronic stroke. [ABSTRACT FROM AUTHOR]

The aim of the study was to examine whether an improvement in jumping performance after 8 weeks of plyometric training (PT) runs in parallel with changes in lower-limb skeletal muscle contractile properties. Using noninvasive tensiomyography (TMG), we assessed contraction time (Tc) and the maximal amplitude of radial displacement (Dm) in 20 subjects (50% men; age 22.4 ± 4.7 years of age), randomly divided in PT group (N = 10; PLYO) and a control group (N = 10; CTRL). The PLYO performed 8 weeks of PT. Tensiomyography was measured in 5 leg skeletal muscles: vastus lateralis (VL), biceps femoris (BF), tibialis anterior (TA), gastrocnemius medialis (GM), and gastrocnemius lateralis (GL). Additionally, we evaluated countermovement jump (CMJ) height improvement on a ground force plate. Assessments were repeated before and after PT. After 8 weeks of PT, CMJ height increased by 12.2% in PLYO (p = 0.015), but not in CRTL. Contraction time, which is related to myosin heavy-chain type 1 (MHC-1) proportion, decreased in VL (-8.7%; p < 0.001), BF (-26.7%; p = 0.032), TA (-32.9%; p = 0.004), and GL (-25.8%; p = 0.044), but not in GM (-8.1%; p = 0.158). The estimated VL MHC-1 proportion decreased by -8.2% (p = 0.041). The maximal amplitude of radial displacement, inversely related to muscle tone, decreased in BF (-26.5%; p = 0.032), GM (-14.9%; p = 0.017), GL (-31.5%; p = 0.017), but not in TA (-16.8%; p = 0.113) and VL (-6.0%; p = 0.654). After PT, jumping performance increased, which was paralleled by decreased Tc and decreased muscle tone. Additionally, adaptations to contractile properties were muscle specific, which is important for future studies. It seems that adjustments were dose dependent, being higher in muscles with lower habitual load. [ABSTRACT FROM AUTHOR]

Changes in range of motion affect the magnitude of the load during the squat exercise and, consequently, may influence muscle activation. The purpose of this study was to evaluate muscle activation between the partial and full back squat exercise with external load equated on a relative basis between conditions. Fifteen young, healthy, resistance-trained men (age: 26 ± 5 years, height: 173 ± 6 cm) performed a back squat at their 10 repetition maximum (10RM) using 2 different ranges of motion (partial and full) in a randomized, counterbalanced fashion. Surface electromyography was used to measure muscle activation of the vastus lateralis, vastus medialis, rectus femoris, biceps femoris (BF), semitendinosus, erector spinae, soleus (SL), and gluteus maximus (GM). In general, muscle activity was highest during the partial back squat for GM (p = 0.004), BF (p = 0.009), and SL (p = 0.031) when compared with full-back squat. There was no significant difference for rating of perceived exertion between partial and full back squat exercise at 10RM (8 ± 1 and 9 ± 1, respectively). In conclusion, the range of motion in the back squat alters muscle activation of the prime mover (GM) and stabilizers (SL and BF) when performed with the load equated on a relative basis. Thus, the partial back squat maximizes the level of muscle activation of the GM and associated stabilizer muscles. [ABSTRACT FROM AUTHOR]

Bilateral squats are frequently used exercises in sport performance programs. Lower extremity muscle activation may change based on knee alignment during the performance of the exercise. The purpose of this study was to compare lower extremity muscle activation patterns during different squat techniques. Twenty-eight healthy, uninjured subjects (19 women, 9 men, 21.5 ± 3 years, 170 ± 8.4 cm, 65.7 ± 11.8 kg) volunteered. Electromyography (EMG) electrodes were placed on the vastus lateralis, vastus medialis, rectus femoris, biceps femoris, and the gastrocnemius of the dominant leg. Participants completed 5 squats while purposefully displacing the knee anteriorly (AP malaligned), 5 squats while purposefully displacing the knee medially (ML malaligned) and 5 squats with control alignment (control). Normalized EMG data (MVIC) were reduced to 100 points and represented as percentage of squat cycle with 50% representing peak knee flexion and 0 and 99% representing fully extended. Vastus lateralis, medialis, and rectus femoris activity decreased in the medio-lateral (ML) malaligned squat compared with the control squat. In the antero-posterior (AP) malaligned squat, the vastus lateralis, medialis, and rectus femoris activity decreased during initial descent and final ascent; however, vastus lateralis and rectus femoris activation increased during initial ascent compared with the control squat. The biceps femoris and gastrocnemius displayed increased activation during both malaligned squats compared with the control squat. In conclusion, participants had altered muscle activation patterns during squats with intentional frontal and sagittal malalignment as demonstrated by changes in quadriceps, biceps femoris, and gastrocnemius activation during the squat cycle. [ABSTRACT FROM AUTHOR]

The article discusses research which was conducted to compare surface electromyographic (sEMG) activity of selected lower extremity and back muscles and examine the impact of ankle positioning during the standard sit and reach test (SRT) and the modified sit and reach test (MSRT). Researchers evaluated seven male and seven female subjects. They found that both tests led to muscle activity and that both tests were able to measure hamstring flexibility.

The article reports on research which was conducted to investigate lower limb and trunk muscle activation in resistance exercise trained men who performed the back squat exercise and the resisted sled exercise. Researchers evaluated 10 men. They found that there were no significant differences between the two exercises seen during an analysis of electromyographic activity of muscles and concluded that either exercise could be used as part of an athletic training program.

The article reports on research which was conducted to investigate the muscle activity in the hamstring muscle and surrounding musculature in weightlifters who performed the leg curl, good morning, glute-ham raise and Romanian deadlift (RDL). Researchers evaluated 12 weight lifters. They found that the semitendinosus is more active than the biceps femoris in all exercises and that the hamstring was maximized in the RDL.

The article reports on research which investigated the influence of age on the viscoelastic stretch response. Researchers evaluated 22 younger and 14 older male subjects. They found that the younger men displayed a greater initial relative stress relaxation response that diminished across repeated stretches, whereas the older men experienced a smaller relative response that remained constant.

The article discusses a study of the impact of stretching on maximal isometric plantar flexion torque which indicates that stretching-induced deficits of torque are reduced within 10 minutes. Topics include maximal voluntary contractions and electromyographic amplitudes among the women tested in trials.

The article presents information on the effect of kinesio taping (KT) on jumping and balance in athletes. Topics discussed include, use of functional taping for stabilizing injured joints, and using KT technique for enhancing normal functional movements and decreasing pain and swelling. Also discussed is the improvement in muscule contraction through KT.

The article presents information on neuromuscular features of drop and hurdle jumps with various types of landings. Topics discussed include effect of landing on jump performance, lower limb plyometric exercises for gaining explosive-reactive movement, and use of elastic energy accumulated in body during plyometric exercises.

The article cites a research study on biomechanical analysis of standing long jump from different starting positions. The study subjects were six high caliber sprinters who performed a series of jumps from parallel and straddle foot placement. The study investigated the effect of the different foot movement by the ground reaction forces analysis and 3-dimensional motion.

The focuses on a study conducted to determine the most effective squat depth in relation to muscle activation for male and female collegiate cross country runners. Joint angles, squat loads and hamstrings to quadriceps ratios were calculated during a training session. No significant differences were found between females and males with respect to joint angles.

The article focuses on a study aimed at examining if normalized and absolute soleus muscle deficits were found in middle aged women compared with middle aged men. Women were found to have less strength in triceps surae complex and the soleus compared to men. They were also found to have less absolute strength compared to men.

The article discusses a study which was aimed to investigate the effects of gradients on biomechanical parameters during racewalking (RW) at iso-efficiency speed (IES). The study included 12 high-level athletes who performed at IES on different slopes. The findings of the study indicated that increasing the gradient to 2% did not elicit an increased HR in racewalkers.

The article reports on research which was conducted to investigate the electromyographic activity of the lower limbs of athletes who performed squatting on a Reebok core board and the ground. Researchers found that the electromyography revealed similar muscle activities in squatting on both surfaces.

The article reports on research which was conducted to perform an electromyographic analysis of the lower limbs of 10 skilled baseball players and 10 unskilled players during batting. Researchers found that that preparations for the batting swing are made earlier in skilled baseball players because they recruit their lower muscles for the swing more effectively than unskilled players.

The article discusses research examining muscle force output and electromyographic activity in squats on a variety of unstable surfaces. The authors compared the force output and muscle activity of leg and trunk muscles in 15 men as they performed isometric squats on a stable surface, a power board, a BOSU exercise ball, and a balance cone. Statistics related to the force output and electromyographic (EMG) activities of muscles on various surfaces are presented.

The article discusses research which was conducted to determine the influence knee flexion angle and age had on triceps surae muscle activity during heel raises. Researchers evaluated 48 health younger aged and middle aged male and female subjects. They found that age did not impact the knee flexion angle and that triceps surae muscle activity was not different between middle aged and younger aged adults.

The article reports on research which was conducted to investigate the influence knee flexion angle and age had on triceps surae muscle fatigue during heel raises. Researchers evaluated 48 younger aged and middle aged subjects who performed heel raises. They found that knee angle did not influence muscle fatigue and that there were no differences seen between the two age groups.

The article reports on research conducted to investigate the effect hyperbaric oxygen therapy had on blood circulation of human muscle and tendon in vivo. Researchers evaluated acute changes in blood volume and oxygen saturation of the medial gastrocnemius muscle and Achilles tendon during oxygen therapy. They found that changes in blood volume in the muscle increased after therapy but that oxygen saturation did not and that in the tendon both blood volume and oxygen saturation increased.

The article discusses research investigating whether a topical magnesium (Mg2+) cream, called MagPro, influences muscle flexibility or muscle endurance. Topics include an overview of the study's experimental design, results of an analysis of variance (ANOVA), and the study's conclusion regarding the influence of MagPro on the outcome measures of the study.

The article discusses research investigating the impact of wearing rocker-bottom shoes with compliant midsoles (RB) on lower extremity muscle activity and the metabolic cost of walking. Researchers recorded muscle activity and oxygen consumption of study participants as they walked on a tread mill wearing various types of shoes including flat-bottomed and flat-bottomed weight-matched to RB. Results showed RB shoes did not increase lower muscle activity or the energy cost of walking.

The article discusses research conducted to identify the effect whole body vibration (WBV) had on the spectral properties of electrically evoked H-reflex recordings in the soleus (SOL) muscle. Researchers evaluated the H-reflex recordings in the SOL muscle of 20 participants before and after a bout of WBV. They found that WBV transiently decreased the intensity of myoelectric spectra during electrically evoked contractions but did not influence the frequency of the spectra.

The article reports on research conducted to investigate the effect compression on gastrocnemius medialis muscle tissue had on oxygenation and hemodynamics during a short term dynamic exercise. Researchers used elastic compression sleeves to apply compression to the calf muscles of 15 male athletes. They found that compression induced changes in tissue blood flow and perfusion appeared to lead to improved oxygenation during short-term exercise.

The article reports on research conducted to investigate the muscle activation pattern of the lower limbs for the stopping motion of baseball batting by recording surface electromyography (EMG). Researchers evaluated 10 baseball players and 10 non-athletes during swinging and stopping. They found that the peak latencies of EMG were significantly shorter in stopping than in swinging in the right tibialis anterior, left biceps femoris and left medial gastrocnemius muscles of both groups.