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The use of the “efficiency of electrical activity” (EEA) technique involves plotting EMG amplitude as a function of force at different percentages of one's maximum strength for a given task, and has been used to examine the time course of neural versus hypertrophic contributions to resistance training-induced strength gains. Though several studies have demonstrated a linear EMG amplitude versus force relationship with a reliable slope coefficient under isometric testing conditions, it is unclear whether the EEA technique may be applied to dynamic muscle actions. The purpose of the present investigation was to examine the linearity and reliability of the EMG amplitude versus dynamic torque relationship for the vastus lateralis (VL). Nine healthy men (mean ± SD age = 25.3 ± 4.7 years) and eleven healthy women (mean ± SD age = 22.0 ± 1.3 years) performed concentric isokinetic muscle actions of the dominant leg extensors at 30°·s-1 on two occasions separated by at least 48 hours. The muscle actions were randomly ordered in 10% increments from 10% to 100% of peak torque. During each muscle action, the surface EMG signal was detected from the VL with a bipolar surface electrode arrangement. (See Table 1). The coefficients of determination ranged from r2 = 0.75-0.98 for trial 1 and 0.64-0.99 for trial 2. The results from a paired-samples t-test indicated that there was no mean difference between the linear EMG amplitude versus torque slope coefficients from trial 1 versus trial 2. The linear EMG amplitude versus torque slope coefficient for trial 1 was significantly different from that for trial 2 for 3 (2 were greater, 1 was smaller) of the 20 subjects. The results from a two-way repeated measures ANOVA indicated that there was no significant trial × torque interaction, and no main effect for trial, but there was a significant main effect for torque. In addition, the intraclass correlation coefficient for the linear EMG amplitude versus torque slope coefficients for trials 1 and 2 were 0.730 (SEM = 4.9% of the mean value). The results of the present study indicated that the relationship between EMG amplitude and dynamic torque for the VL did not display an adequate degree of linearity and reliability to be used for the EEA technique. The EEA technique is important in addressing issues such as the neural versus hypertrophic contributions to resistance training-induced strength gains and the mechanisms underlying cross-education. The results of this study suggested that these topics should not be investigated with the use of dynamic muscle actions of the VL.Table 1. Coefficients of determination (r2) and linear slope coefficients for the electromyographic (EMG) amplitude versus torque relationships for trials 1 and 2 for the vastus lateralis (VL) of each subject. [ABSTRACT FROM AUTHOR]

Many previous studies have reported a temporary decrease in muscle strength following an acute bout of stretching, which has been termed the “stretching-induced force deficit.” It has also been suggested that the stretching-induced force deficit may be joint angle-specific and influenced by initial level of flexibility. To examine the effects of initial flexibility on the stretching-induced force deficit in the plantar flexor muscles at multiple joint angles and ankle joint range of motion (ROM). Fourteen men with limited dorsiflexion ROM (mean age ± SD = 21 ± 2 yrs; stature = 173 ± 9 cm; mass = 75 ± 12 kg; dorsiflexion ROM = 11 ± 6°) and 14 men with a normal ROM (22 ± 2 yrs; 177 ± 8 cm; 75 ± 14 kg; 28 ± 6°) (Roaas et al. 1982, Acta Othropedic 53(2): 205 - 208) performed stretch tolerance assessments and isometric maximal voluntary contractions (MVCs) at -19°, -9°, 1°, and 12° of dorsiflexion (0° = neutral ankle joint angle) designed to examine the ROM and strength, respectively. Testing was performed on a custom-built load cell apparatus attached to a calibrated isokinetic dynamometer before and after a bout of passive stretching. To assess stretch tolerance, the dynamometer lever arm passively dorsiflexed the foot at 5°·s-1 from -20° of dorsiflexion to the maximum tolerable ROM (as acknowledged by the subjects). For the MVC assessments, subjects were instructed to provide maximal force of the plantar flexors for 4 s at each randomly-ordered joint angle. The position signal (°) from the dynamometer and force signal (N) from the load cell were sampled at 1 KHz during the flexibility and strength assessments, respectively. The passive stretching protocol consisted of nine 135-s constant-torque passive stretches, which was held by the dynamometer at each subject's maximum tolerable passive stretching force (the point of discomfort). Five to 10 s was allowed between each stretching repetition. A three way mixed factorial ANOVA [time × angle × group; 2 × 4 × 2] was used to analyze the MVC data, while a two way mixed factorial ANOVA [time × group; 2 × 2] was used to analyze the ROM data. There was a 9% decrease in plantar flexor MVC strength from pre- to post-stretching across all joint angles for both groups (p < 0.001). Conversely, there was a 4% increase in dorsiflexion ROM from pre- to post-stretching for both groups (p < 0.001), however, the normal ROM group had higher dorsiflexion ROM values than the limited ROM group (p < 0.001) at all time points. The magnitude of change for MVC strength and dorsiflexion ROM from pre- to post-stretching was not affected (p > 0.05) by the joint angle or limitations of ROM. These findings suggested that the initial level of flexibility does not influence the force deficit or increases in dorsiflexion ROM following an acute bout of passive stretching in the plantar flexor muscles. These results also indicated that the stretching-induced force deficit occurs at all the ankle joint angles tested. These findings may be useful for strength and conditioning professionals or other allied health practitioners who may incorporate stretching prior to testing or performance. Regardless of initial flexibility, 20 min of passive stretching appears to increase dorsiflexion ROM, but decrease the maximal strength capabilities of the plantar flexors at all of the joint angles tested in the present study. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to evaluate Dual-energy X-ray absorptiometry (DXA) for estimating fat mass (FM), percent fat (%FAT), and fat-free mass (FFM) in older men and women compared to a four-compartment model (4C). Forty men and women (65-84yr, 20 men and 20 women) participated in the study. Body fat calculations included a criterion 4C model and DXA-derived FFM, %FAT, and FFM. The criterion 4C model included body volume from air-displacement plethysmography (ADP), total body water from deuterium dilution, and bone mineral content from DXA. Constant error (CE), standard error of estimate (SEE), total error (TE), and the 95% limits of agreement were used to compare DXA values to the 4C model. All DXA mean values (CE) were significantly different than the 4C model. DXA %fat values were the least accurate with the largest TE and a y-intercept significantly different than zero (p = 0.035). Bland and Altman analysis indicated that no DXA-derived value produced a significant trend. Compared to DXA, the Siri two-compartment (2C) model using ADP produced non-significant (p > 0.106) CE values, lower TE values ( < 1.66), lower SEE values ( < 1.65), and smaller individual errors (95% limits of agreement < 3.17). DXA appears to be biased in older men and women when comparing mean values of FM, FFM, and %FAT compared to a 4C model. %FAT produced the largest individual errors with limits of agreement ± 5.23%FAT. However, DXA produced acceptable TE values and can be considered a valid method for predicting body composition. Nonetheless, regardless of the significant CE values for DXA, using ADP alone in a 2C model produced more accurate, non-biased results compared to the 4C model for all values, as indicated by a reduced SEE and smaller individual errors. FM and FFM DXA values were more accurate than %FAT values compared to a 4C model. However, the Siri 2C model was more accurate than all DXA derived values. Additionally, DXA produced significantly different FM, FFM, and %FAT values compared to a 4C model. Therefore, DXA is not suggested for use in older men and women when attempting to predict FM, FFM, or %fat. Furthermore, choosing ADP for use in the Siri 2C model to predict FM, FFM, and %FAT appears to be more accurate than DXA in this population.Table 1. No Caption Available. [ABSTRACT FROM AUTHOR]

The critical power test provides two measures, critical power (CP) and anaerobic working capacity (AWC). In theory, the CP measurement represents the maximal power output that can be maintained without fatigue, which is regarded as an aerobic measure. AWC is an estimate of work capacity associated with muscle energy reserves adenosine triphosphate (ATP) and phosphocreatine (PCr). High- intensity interval training (HIIT) has been shown to be an effective training method for improving endurance performance, including CP and AWC measures. In addition, creatine (Cr) supplementation has been reported to improve AWC without training; however, Cr had no effect on CP. To date, no one has examined the effect of Cr supplementation during HIIT on CP and AWC. The purpose of this study was to examine the effects of four weeks of HIIT in conjunction with Cr supplementation on CP and AWC in college-aged men. Forty-two recreationally active men (mean ± SD; age 23.62 ± 4.78 yrs; height: 177.48 ± 7.05 cm; weight: 82.23 ± 12.70kg) volunteered to participate in this study. Participants were assigned to one of three groups: Cr (n = 16) 10g Cr + 10g dextrose powder blend; placebo (PL, n = 16) 20g dextrose powder blend; control (CON, n = 10) no treatment. Prior to and following supplementation, each participant performed a continuous maximal oxygen consumption test (o2PEAK) on a cycle ergometer to establish peak power output (PPO). Participants then completed a CP test, consisting of three exercise bouts to exhaustion with the workloads set as a percentage of their PPO to determine CP and AWC. Following initial testing, a 2-week familiarization period of training and supplementing occurred. Baseline values were then measured and all participants in the Cr and PL groups engaged in 4 weeks of HIIT training on a cycle ergometer. Training consisted of either five or six sets of 2-minutes work with 1-minute passive rest, five days per week. Training intensity followed an undulating model starting at 80% PPO and reaching 120%. Significant two-way interactions [time (base- vs. post-) × treatment (Cr vs. PL vs. CON)] were discovered for CP (p = 0.007). Follow-up analyses indicated that the Cr group increased 6.72% ± 2.54%, while PL and CON showed no significant change in CP (3.87% ± 2.30% and -6.27% ± 2.38%, respectively). Furthermore, no changes in AWC were observed in any of the groups following treatment. The current findings suggest that the HIIT and supplementation protocol may be an effective method for improving CP, but had no effect on AWC. It would appear that Cr supplementation may enhance the effect of intense interval endurance training on aerobic performance changes as measure by the CP test. ACKNOWLEGMENTS: This investigation was supported by FSI Nutrition, Omaha, Nebraska. [ABSTRACT FROM AUTHOR]

To examine musculotendinous stiffness (MTS) and ankle joint range of motion (ROM) in men and women following an acute bout of passive stretching. Eight men (mean ± SD age = 20.3 ± 2.0 yrs; body mass = 78.8 ± 12.3 kg; height = 176.6 ± 5.8 cm) and nine women (age = 21.0 ± 2.4 yrs; body mass = 61.7 ± 7.4 kg; height = 166.3 ± 7.5 cm) volunteered for this study. To avoid any menstrual cycle differences, the women were all tested during menses. Each subjects foot was stabilized in a custom-built apparatus designed to measure plantar flexion force with a knee joint angle of 180° and ankle joint angle of 90°. The apparatus was also attached to a powered isokinetic dynamometer that stretched the plantar flexor muscles by passively dorsiflexing the foot at 5°·s-1 until a constant-torque threshold was achieved and held at a point of discomfort as acknowledged by the subject. Nine repetitions of each stretch were held for 135 s with 10 s of rest between repetitions. Before and after the stretching, a maximal, passive flexibility assessment was performed, in which subjects were asked to relax while their foot was maximally dorsiflexed at 5°·s-1. Passive torque and position were recorded from the isokinetic dynamometer. To calculate MTS, the ankle joint angle (°) and torque (Nm) signals were sampled at 1 KHz during the flexibility assessments and plotted as torque-angle curves (i.e., stress-strain curves). Each subject's curve was fit with a 4th-order polynomial regression model (Nordez et al. 2006, Clin Biomech, 21:755-760), and MTS was calculated as the slope (Nm°-1) of the tangent to the curve at a 90° joint angle. MTS decreased by 15.4% (p < 0.001) in men and 36.7% (p < 0.001) in women from pre- to post-stretching. Passive range of motion (PROM) increased by 3.1% (p = 0.018) in men and 7.3% (p = 0.001) in women from pre- to post-stretching. No differences (p > 0.05) were observed between men and women for PROM and MTS prior to and post-stretching. However, the percent change scores from pre- to post-stretching for MTS (p = 0.021) and PROM (p = 0.036) were greater for the women than the men. These findings suggested that 20 min of constant-torque passive stretching increased the PROM and decreased the MTS of the plantar flexors in both men and women, although the magnitude of the change was greater for the women. The greater decrease in MTS and increase in PROM for women may have been due to gender-specific differences in viscoelastic creep during the constant-torque stretching procedures. It has been suggested that a decrease in MTS reduces the total amount of strain through a given ROM, which may reduce the risk of strain injuries. Therefore, the findings of this study suggest that men may have to stretch for a longer duration or at a greater intensity to achieve similar increases in ROM and decrease in MTS as women.Figure 1. No Caption Available. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the mechanomyographic (MMGRMS) and electromyographic (EMGRMS) amplitude vs. force relationships of the vastus lateralis (VL) for aerobically-trained (AT), resistance-trained (RT), and sedentary individuals (SED). Five RT (mean ± SD age = 23 ± 3 yrs; body mass = 101 ± 37 kg; height = 176 ± 8 cm), 5 AT (32 ± 5 yrs; 67 ± 4 kg; 176 ± 2 cm), and 5 SED (23 ± 4 yrs; 93 ± 32 kg; 180 ± 5 cm) men volunteered to perform two 6-s isometric ramp muscle actions from 5% to 100% of their maximal voluntary contraction (MVC) while MMG (m·s-2) and EMG (μV) signals were recorded from the VL muscle. Thigh skinfold measurements and Bergstrom muscle biopsies were taken from the VL. The muscle samples were analyzed for myosin heavy chain (MHC) isoform content. Simple linear regression models were fit to the natural log-transformed EMGRMS and MMGRMS vs. force relationships. The slope (b term) and the antilog of the Y-intercept (a term) were calculated for each relationship. For %MHC, the AT group had a greater percentage of type I fibers than the RT and SED groups (p ≤0.05). The RT group had a greater percentage of type IIa fibers than the AT group (p ≤0.05), and the SED group had a greater percentage of type IIx fibers than the AT and RT groups (p ≤0.05). For both the log-transformed EMGRMS and MMGRMS vs. force relationships, the mean a term for the AT group was higher than the RT and SED groups (p ≤0.05). For the log-transformed MMGRMS vs. force relationships, however, the b term for the AT group was lower than the RT and SED groups (p ≤0.05). There were no differences (p >0.05) among the b terms of the AT, RT, and SED groups for the log-transformed EMGRMS vs. force relationships. In addition, the mean skinfold for the SED group was higher than the AT group (p ≤0.05) (AT = 8.7 ± 2.2mm, RT = 15.4 ± 7.6mm, and SED = 25.4 ± 9.2mm). The group-related differences among the a terms for both the log-transformed EMGRMS and MMGRMS patterns might be best explained by the group differences in skinfold thickness. However, the fact that the AT group had a lower mean b term for the log-transformed MMGRMS vs. force relationships may suggest that the differences in motor control strategies between individuals with predominantly type I vs. type II fibers in the vastus lateralis could be detectible with the MMG signal, but not EMG. The lower b term for the AT group suggested that the MMG-force relationship may have been sensitive to the earlier achievement of rate coding, whereas the RT and SED groups relied more on motor unit recruitment to reach higher force levels. The b terms from the EMGRMS vs. force relationships were unable to differentiate among the groups. The log-transformed MMGRMS, but not EMGRMS, vs. force relationships may be useful as non-invasive measurements to determine the onset of rate coding, which may differ among muscles that are predominantly type I vs. type II fiber types. Therefore, the MMG signal may offer an attractive, simple technique for examining changes in the motor control strategies that govern incremental isometric force production. [ABSTRACT FROM AUTHOR]