Search

To investigate the kinematic and muscle activation adaptations during performance of the Nordic hamstring exercise (NHE) to a 6-week eccentric hamstring training programme using the NHE as the sole mode of exercise.Twenty-nine healthy males were randomly allocated to a control (CG) or intervention (IG) group. The IG participated in a 6-week eccentric hamstring exercise programme using the NHE.The findings of the present study were that a 6-week eccentric hamstring training programme improved eccentric hamstring muscle strength (202.4 vs. 177.4 nm, p = 0.0002, Cohen's d = 0.97) and optimized kinematic (longer control of the forward fall component of the NHE, 68.1° vs. 73.7°, p = 0.022, Cohen's d = 0.90) and neuromuscular parameters (increased electromyographic activity of the hamstrings, 83.2 vs. 56.6 % and 92.0 vs. 54.2 %, p0.05, Cohen's d1.25) associated with NHE performance.This study provides some insight into potential mechanisms by which an eccentric hamstring exercise programme utilizing the NHE as the mode of exercise may result in an improvement in hamstring muscle control during eccentric contractions.

This study compared the heart rate (HR) and blood lactate (BL) responses in young healthy women performing the same routine of aerobics exercise in 3 different conditions: on land, in shallow water (0.8 m), and in deep water (1.4 m). The average age and body mass index (BMI) of the group were 27.4 years and 22.6 kg.m(-2), respectively. The highest HR and BL values were reached during land aerobics (median HR values were 138.0 and 161.5 b.min(-1), and lactate values were 3.10 and 5.65 mmol.L(-1) at slow and at faster pace, respectively). These parameters were progressively reduced going from shallow water (121.5 and 154.0 b.min(-1), 1.75 and 3.15 mmol.L(-1)) to deep water (97.5 and 113.5 b.min(-1), 1.70 and 1.75 mmol.L(-1)). The HR measured as percentage of maximum HR varied from 48.43% to 77.53% depending on the water depth and the pace. These data indicate that exercise in water significantly reduces HR and BL production compared with the same exercise performed on land.

The aim of this study was to investigate the benefits of a low-volume, vigorous intensity bench stepping programme in sedentary middle-aged adults. Thirty-one healthy but sedentary adults (12 men; 55-64 years) took part in the study. Participants accumulated up to 9 min per day of stepping exercise on three days per week over the 4-week experimental period. Parameters of cardiorespiratory fitness, body composition and lower limb muscle strength were measured on three occasions: TS1 (baseline test), TS2 (following a 4-week control period) and TS3 (following the 4-week intervention). Data were analysed using a repeated-measures ANOVA. Adherence to the programme was excellent (96%). Relative to the insignificant changes following the control period, parameters of cardiorespiratory fitness were significantly improved following training. No alterations in body composition or lower limb muscle strength were detected. These results show that less than 30 min per week of bench step exercise, accumulated in short bouts throughout the day, can improve parameters of cardiorespiratory fitness after only 4 weeks in previously sedentary middle-aged adults. Due to its low-cost, time-efficient and discrete aspects, stepping exercise may have important implications for public health initiatives that promote physical activity in a population who commonly report 'lack of time' as a barrier to physical activity.

Background Stiffness properties of the knee joint and landing biomechanics are important factors linked to injury risk. Neuromuscular training may mitigate the risk injury and simultaneously improve sports performance. Objective To investigate the effect of neuromuscular training on the stiffness properties of the knee joint and landing biomechanics of young female recreational athletes. Design Quasi-experimental study. Setting Biomechanics laboratory. Participants Twenty-six female recreational athletes. Interventions Intervention group: combined plyometric (drop jump movements, cutting techniques with quick reactions and maximal effort) and resistance (body-weight, dumbbell and Thera-Band® exercises) training, 3 times/week for 6 weeks; control group: regular physical activity. Main Outcome Measurements Peak torque of the knee extensors, relaxed and contracted muscle stiffness of the vastus lateralis, knee joint musculoarticular stiffness (MAS), and drop vertical jump (DVJ) performance were assessed pre- and post-intervention. Results Post-intervention MAS increased significantly (pre- 1657.58±338.53 Nm−1, post- 1930.79±419.15 Nm−1) in the intervention group only. Additionally, compared with the control group the intervention group exhibited an increased rate of torque development (pre- 905.13±90.31 Nms−1, post- 1076.35±93.14 Nms−1), decreased knee valgus (pre- 7.86±5.86 °; post- 2.48±5.34 °), increased maximum knee flexion (pre- 73.17±9.32 °; post- 79.68±9.70 °), increased flight time (pre- 0.43±0.04 s; post- 0.46±0.03 s), an increase in DVJ height (pre- 0.23±0.04 m; post- 0.26±0.04 m), as well as decreased peak ground reaction force of the first (pre- 2.44±0.60 Nkg−1; post- 1.83± 0.47 Nkg−1) and second landings (pre- 2.34±0.86 Nkg−1; post- 2.06±0.92 Nkg−1) of the DVJ. Conclusions Neuromuscular training can improve the stiffness characteristics of the knee joint and landing biomechanics of recreational female athletes.

The assessment of musculo-articular stiffness (MAS) with the free-oscillation technique is a popular method with a variety of applications. This study examined the sources of variability (load applied and frequency of oscillation) when MAS is assessed. Over two testing occasions, 14 healthy men (27.7±5.2 yr, 1.82±0.04 m, 79.5±8.4 kg) were measured for isometric maximum voluntary contraction and MAS of the knee flexors using submaximal loads relative to the individual's maximum voluntary contraction (MAS%MVC) and a single absolute load (MASABS). As assessment load increased, MAS%MVC (coefficient of variation (CV) = 8.1-12.1%; standard error of measurement (SEM) = 51.6-98.8 Nm⁻¹) and frequency (CV = 4.8-7.0%; SEM = 0.060-0.075 s⁻¹) variability increased consequently. Further, similar levels of variability arising from load (CV = 6.7%) and frequency (CV = 4.8-7.0%) contributed to the overall MAS%MVC variability. The single absolute load condition yielded better reliability scores for MASABS (CV = 6.5%; SEM = 40.2 Nm⁻¹) and frequency (CV = 3.3%; SEM = 0.039 s⁻¹). Low and constant loads for MAS assessment, which are particularly relevant in the clinical setting, exhibited superior reliability compared to higher loads expressed as a percentage of maximum voluntary contraction, which are more suitable for sporting situations. Appropriate sample size and minimum detectable change can therefore be determined when prospective studies are carried out.

Introduction While it is known that acute intense exercise promotes the generation of oxidative stress (OS), the role of intermittency in this paradigm is unclear. Thus, the aim of the present study was to assess the impact of exercise intermittency on markers of OS. Methods Nine (n = 9) healthy males of an average age of 22.6 yrs (range 21 – 27 yrs) volunteered for the study. Participants were randomly assigned to complete a low (80s work:rest) moderate (20s work:rest) or high (5s work:rest) intermittent exercise protocol using a cross-over design on a non-motorised treadmill. The total work completed was equivalent across each of the conditions in terms of mean speed and duration (45mins). Fasted venous blood samples were collected pre, 1-h, 2-h and 24-h post exercise for the analysis of lipid hydroperoxides (LOOHs), superoxide dismutase (SOD), and glutathione (GSH) via plate reader methods while 8-Oxo-2'-deoxyguanosine (8-oxo-dG) was analysed using LC-MS. Results Analysis of DNA damage showed no detectable levels of 8-oxo-dG across all exercise protocols. LOOHs increased on average by 69% (range -6 − 427%), SOD by 52% (range -49 − 590%) and GSH by 99% (range -47.7 − 179%) in the low intermittent group 2hrs post exercise, whereas moderate and high intermittency did not demonstrate any relevant changes. Discussion It is presented that OS was found to increase 2hrs after a bout of high intensity/low intermittent exercise. It is plausible that the higher intermittent modes were not of sufficient duration to trigger the signaling cascade associated with exercise, free radical formation and subsequent OS. It was also further determined that plasma concentrations of 8-oxo-dG were below the limit of detection of LC-MS (0.25nM) and further consideration should be given to choice of sample type when investigating this important biological marker.

Introduction: The aim of this cross-sectional study was to concurrently assess musculo-articular stiffness (MAS) and muscle stiffness (MS) of the knee extensors in younger and older individuals. Methods: Fourteen young (22.1 ± 3.0 years old) and 12 older (65.4 ± 5.7 years old) men were tested for maximal voluntary contraction (MVC), rate of torque development (RTD), muscle thickness, MAS, and MS of knee extensors. Results: MVC, RTD, and muscle thickness were higher in the younger group (288.6 vs. 194.3 Nm, 1319.5 vs. 787.0 Nm s−1, 23.1 vs. 17.7 mm, respectively, P < 0.05). MAS normalized to the load supported (30% of MVC) was not different between groups (87.9 vs. 88.5 Nm−1kg−1), whereas the older group exhibited a higher level of normalized MS (23.2 vs. 18.6 Nm−1kg−1, P < 0.05). Conclusions: Determinants of MS have been highlighted along with their role in elevated MS. The unaltered level of MAS, which is functionally important in an aging population, might be achieved through a decrease in tendon stiffness. Muscle Nerve 46: 559–565, 2012

Despite its widespread use in performance assessment, the reliability of vertical jump in an ageing population has not been addressed properly. The aim of the present study was to assess intra- and inter-day reliability of countermovement jump in healthy middle-aged (55-65 years) and older (66-75 years) men and women. Eighty-two participants were recruited and asked to perform countermovement jumps on two different occasions interspersed by 4 weeks. The middle-aged groups exhibited excellent absolute reliability for flight height, jump height, peak force, peak power, peak force/body mass, and peak power/body mass, with coefficients of variation ranging from 2.9% to 7.2% in men and from 3.6% to 6.9% in women and moderate-to-high intraclass correlations (0.75 to 0.97 in men; 0.77 to 0.95 in women). The older groups displayed good coefficients of variation (4.2% to 10.8% in men and 3.4% to 9.5% in women), but the intraclass correlations were low-to-high (0.43 to 0.84 in men; 0.42 to 0.93 in women). Overall, intra-session reliability was higher than inter-session reliability. Peak power was by far the most consistent variable, whereas flight and jump height had the most marked variability. The minimum detectable change varied from 10.5% to 33%, depending on the variable examined, suggesting important implications for intervention studies.

Exercise induced muscle damage (EIMD) impairs maximal torque production which can cause a decline in athletic performance and/or mobility. EIMD is commonly assessed by using maximal voluntary contraction (MVC), creatine kinase (CK) and muscle soreness. We propose as an additional technique, tensiomyography (TMG), recently introduced to measure mechanical and muscle contractile characteristics. The purpose of this study was to determine the validity of TMG in detecting changes in maximal torque following EIMD. Nineteen participants performed eccentric elbow flexions to achieve EIMD on the non- dominant arm and used the dominant elbow flexor as a control. TMG parameters, MVC and rate of torque development (RTD) were measured prior to EIMD and repeated for another six consecutive days. Creatine kinase, muscle soreness and limb girth were also measured during this period. Twenty four hours after inducing EIMD, MVC torque, RTD and TMG maximal displacement had significantly (p

Purpose: It was recently demonstrated that musculoarticular (MA) stiffness is related to sprint cycling performance in nonfatigued conditions. This study examined whether relatively stiffer cyclists were more effective at sprinting under fatigued conditions, as occurs during endurance cycling competitions. Methods: MA stiffness of the quadriceps was assessed in 21 trained male cyclists (28.7 ± 9.5 yr, 1.74 ± 0.08 m, 67.5 ± 7.2 kg). Participants also performed a maximal 6-s sprint on a cycle ergometer to assess peak power output (POpeak), peak crank torque (CTpeak), and peak rate of crank torque development (RCTDpeak). A cycling fatigue protocol then required cyclists to pedal at 30%, 35%, and 40% of PO peak and sprint at the end of each stage. Surface EMG was recorded from vastus lateralis during each sprint and analyzed in the time domain as integrated EMG (iEMG) and in the frequency domain as instantaneous median frequency (MDF) adopting a continuous wavelet transform. Participants were then retested for MA stiffness. Results: MA stiffness (-12%) was significantly reduced after the cycling protocol. Further, POpeak, CT peak, RCTDpeak, and iEMG were reduced by 20%, 15%, 13%, and 20%, respectively, after the fatigue protocol (P < 0.05). When the cyclists were divided into relatively stiff (SG) and relatively compliant groups (CG), only SG exhibited significant decreases in MA stiffness, CT peak, RCTDpeak (P < 0.05), and instantaneous MDF (R = 0.705). Conclusions: Whereas neuromechanical parameters were generally reduced under conditions of fatigue, stiff and compliant cyclists were affected differently, with the sprint abilities of SG decreased to the level of CG. It seems important for endurance cyclists to incorporate training strategies to maintain MA stiffness during competition to offset declines in sprint performance. © 2011 by the American College of Sports Medicine.

Portable tensiomyography (TMG) and myotonometry (MMT) devices have been developed to measure mechanical and contractile properties of skeletal muscle. The aim of this study was to explore the sensitivity of the aforementioned techniques in detecting a change in passive mechanical properties of the biceps femoris (BF) muscle as a result of change in knee joint angle (i.e. muscle length). BF responses were assessed in 16 young participants (23.4 ± 4.9 years), at three knee joint angles (0°, 45° and 90°), for maximal isometric torque (MIT) along with myo-electrical activity. Contractile and mechanical properties were measured in a relaxed state. Inter-day reliability of the TMG and MMT was also assessed. MIT changed significantly (p < 0.01) across the three angles, so did stiffness and other parameters measured with MMT (p < 0.01). Conversely, TMG could detect changes only at two knee angles (0° and 45°, p < 0.01), when there is enough tension in the muscle. Reliability was overall insufficient for TMG whilst absolute reliability was excellent (coefficient of variation < 5%) for MMT. The ability of MMT more than TMG to detect an inherent change in stiffness can be conceivably exploited in a number of clinical/therapeutic applications that have to do with unnatural changes in passive muscle stiffness.

The purpose of this study was to assess the validity and inter-day reliability of musculo-articular stiffness (MAS) in the knee-extensor (KE) and knee-flexor (KF) muscle groups, measured with a free-oscillation technique. Fourteen participants were measured, on two occasions, for KE and KF maximal isometric voluntary contraction, rate of torque development (RTD) and electromechanical delay (EMD), along with MAS using multiple sub-maximal loads relative to the individual's maximal voluntary contraction (MAS%MVC). Furthermore, 18 participants were tested for MAS using one fixed assessment load for each muscle group (MASFL) during a separate series of tests on three occasions. MAS%MVC was significantly increased as load increased both in KE and in KF (p

WATSFORD, M., M. DITROILO, E. FERNANDEZ-PENA, G. D'AMEN, and F. LUCERTINI. Muscle Stiffness and Rate of Torque Development during Sprint Cycling. Med. Sci. Sports Exerc., Vol. 42, No. 7, pp. 1324-1332, 2010. Purpose: Crank torque (CT) application and rate of CT development (RCTD) are important considerations in sprint cycling. The stiffness of the musculotendinous unit is related to the isometric rate of torque development (RTD); however, this relationship has yet to be examined in sprint cycling. Methods: Maximal isometric torque (MIT) and isometric RTD of the quadriceps were assessed in 21 trained male cyclists (28.7 T 9.5 yr, 1.74 T 0.08 m, and 67.5 T 7.2 kg). Unilateral musculoarticular (MA) stiffness of the quadriceps was quantified using an oscilla- tion test. Further, the participants performed a maximal 6-s sprint to assess peak power output (POpeak), peak CT (CTpeak), peak RCTD (RCTDpeak), and the crank angles associated with CTpeak and RCTDpeak. Participants were ranked on MA stiffness properties and were divided into a relatively stiff group (SG) and a relatively compliant group (CG). Results: The SG displayed a significantly higher MA stiffness than the CG (P G 0.05). Furthermore, the SG reported significantly elevated MIT (27%), RTD (26%), and RCTDpeak (16%) when compared with the CG (P G 0.05), along with trends for increased POpeak (7%) and CTpeak (8%). The angles at CTpeak and RCTDpeak were 7% and 12% lower for the SG, respectively (P G 0.05). MA stiffness was significantly correlated with RCTDpeak, MIT, RTD, and POpeak. Conclusions: Higher stiffness is related to superior RCTDpeak in trained cyclists during a single sprint. A significant proportion of the variance in RCTDpeak was attributed to MA stiffness (37%), which was of greater magnitude than the relationship between RCTDpeak and MIT. Furthermore, the lower CTpeak angle and RCTDpeak angle may contribute to a more rapid development of

In cycling, a circular pedaling action makes the most useful contribution to forward propulsion. Training with independent cranks (IC) has been proposed to improve the pedaling action. The aims of this study were, first, to assess whether the intermuscular coordination pattern of the pedaling action with normal cranks (NC) is modified after a training period with IC and, second, to determine if the new coordination pattern is maintained after a washing-out period. Eighteen cyclists, divided into a control (CG) and an experimental (EG) group, underwent 2 test sessions (T1 and T2) separated by 2 weeks of training (18 hours). The electromyographic (EMG) activity of 4 lower limbs' muscles was recorded while the athletes pedaled at 80 rpm for 60 seconds at 30 and 50% of the maximal power output determined during a maximal pedaling test. The tasks were performed with IC (EG) and NC (EG and CG). The EG underwent a retention test session (T3) after another 18-hour training with NC. EG showed a significant (45.8 +/- 8.8 vs. 36.0 +/- 6.1%, p0.01 at 30% intensity) and a quasi-significant (62.7 +/- 10.3 vs. 54.2 +/- 8.7%, p = 0.09 at 50% intensity) decrease in vastus lateralis EMG activity and a quasi-significant (36.4 +/- 13.4 vs. 43.5 +/- 10.9%, p = 0.09 at 30% intensity) and a significant (54.5 +/- 12.1 vs. 65.5 +/- 16.1%, p0.05 at 50% intensity) increase in biceps femoris EMG activity between T1-NC and T2-NC. By T3, EMG activity returned to initial levels (T1). On the contrary, CG did not reveal any significant variation. The results provide scientific support for muscle coordination pattern alteration from the use of IC, potentially achieving a more effective pedaling action. IC training reduces quadriceps exertion, thus preserving it for important moments during competition.

An isometric maximal voluntary contraction (iMVC) is mostly used for the purpose of EMG normalization, a procedure described in the scientific literature in order to compare muscle activity among different muscles and subjects. However, the use of iMVC has certain limitations. The aims of the present study were therefore to propose a new method for the purpose of EMG amplitude normalization in cycling and assess its reliability. Twenty-three cyclists performed 10 trials of a maximal isokinetic protocol (MIP) on a cycle ergometer, then another four sub-maximal trials, whilst the EMG activity of four lower limbs muscles was registered. During the 10 trials power output (CV=2.19) and EMG activity (CV between 4.46 and 8.70) were quite steady. Furthermore, their maximal values were reached within the 4th trial. In sub-maximal protocol EMG activity exhibited an increase as a function of exercise intensity. MIP entails a maximal dynamic contraction of the muscles involved in the pedalling action and the normalization session is performed under the same biomechanical conditions as the following test session. Thus, it is highly cycling-specific. MIP has good logical validity and within-subject reproducibility. Three trials are enough for the purpose of EMG normalization in cycling.

Background and aim In this study we developed a new methodology for obtaining human skeletal muscle samples to evaluate gene expression. This approach is based on a fine needle aspiration technique, which allows us to extract a small tissue sample in a significantly less invasive manner than with classic biopsy. Methods and results Multiplex tandem RT-PCR was used to determine the mRNA levels of genes involved in ATP production and mitochondrial biogenesis in muscle tissue. Samples of vastus lateralis muscle were obtained from 21 healthy subjects with different fitness levels. The principal findings in our study show a strong correlation between PGC-1α and COX5B ( p p =0.017) expression. Furthermore, a significant positive correlation between mtDNA content and the percentage of MHCI present in the aspired samples were found ( p =0.028). These data are in agreement with current knowledge on skeletal muscle physiology and show the reliability of the proposed method. Conclusion This painless methodology can be used to investigate, in vivo , human muscle RNA and DNA adaptations in response to either physiological and/or pharmacological stimuli. This method has major clinical relevance, such as its application in clarifying the mechanisms underling metabolic and systemic disorders.

The main purpose of this study was to measure the post-competition blood lactate concentration ([La](b)) in master swimmers of both sexes aged between 40 and 79 years in order to relate it to age and swimming performance. One hundred and eight swimmers participating in the World Master Championships were assessed for [La](b) and the average rate of lactate accumulation (La'; mmol l(-1) s(-1)) was calculated. In addition, 77 of them were also tested for anthropometric measures. When the subjects were divided into 10-year age groups, males exhibited higher [La](b) than women (factorial ANOVA, P0.01) and a steeper decline with ageing than female subjects. Overall, mean values (SD) of [La](b) were 10.8 (2.8), 10.3 (2.0), 10.3 (1.9), 8.9 (3.2) mmol l(-1) in women, and 14.2 (2.5), 12.4 (2.5), 11.0 (1.6), 8.2 (2.0) mmol l(-1) in men for, respectively, 40-49, 50-59, 60-69, 70-79 years' age groups. When, however, [La](b) values were normalised for a "speed index", which takes into account swimming speed as a percentage of world record, these sex-related differences, although still present, were considerably attenuated. Furthermore, the differences in La' between males and females were larger in the 40-49 age group (0.34 vs 0.20 mmol l(-1) s(-1) for 50-m distance) than in the 70-79 age group (0.12 vs 0.14 mmol l(-1) s(-1) for 50-m distance). Different physiological factors, supported by the considered anthropometric measurements, are suggested to explain the results.

Gatta, G., P. Benelli, and M. Ditroilo. The decline of swimming performance with advancing age: A cross-sectional study. J. Strength Cond. Res. 20(4):932-938. 2006.-The aim of this cross-sectional study was to measure the swimming parameters-speed (V), stroke frequency (SF), and stroke length (SL)- in 162 male athletes aged 50-90 (divided into 7 age groups, from A to G) participating in the World Master Championships in the 200-m freestyle event, and to analyze the rates and magnitudes of their age-associated declines. The swimmers were video-recorded by 2 digital cameras during the competitions and the swimming parameters related to every 50-m section (lap) and to the entire race (average) subsequently measured or calculated. Lap V and SF decreased in the second and third quarter (11 and 4% on average) and increased (3% on average) in the fourth quarter of the race, whereas lap SL decreased from the first to the last 50-m section. Average V (m·s?1) decreased from 1.39 ± 0.09 (group A) to 0.84 ± 0.11 (group G); average SL (m) decreased from 2.10 ± 0.20 (group A) to 1.78 ± 0.19 (group G); and average SF (cycles·s?1) decreased from 0.67 ± 0.06 (group A) to 0.47 ± 0.04 (group G). One-way analysis of variance showed significant declines in average V, SL, and SF (p < 0.01) across the 7 groups. The swimming parameters were normalized to the highest values (set equal to 100); thereafter, a linear regression curve was fitted and the regression equations calculated. Decline of SF was about 2.5 times steeper than that of SL. It was highlighted that (a) among the swimming parameters, SL is less affected by the ageing process; (b) SL decreased from group A through group C and thereafter tended to keep steady, whereas the trend for SF was opposite. The results have the potential to give master swimmers and their coaches useful information for training program design.

Background Appropriate levels of muscle strength, muscle stiffness (MS) and musculoarticular stiffness (MAS) are important factors linked to athletic performance. Alterations in knee joint mechanical behavior induced by neuromuscular fatigue may have implications for injury susceptibility. Objective To investigate the acute effects of fatigue on peak torque of the knee joint extensor musculature, MS of the vastus lateralis and MAS of the knee joint in young male athletes. Design Experimental study. Setting University biomechanics laboratory. Participants 27 male recreational athletes. Interventions A 15-minute cycle ergometer fatiguing protocol. Main outcome measurements Peak torque of the knee joint extensor musculature was assessed on a leg-extension dynamometer, whilst MS of the vastus lateralis was measured using a myometer (Muomeetria AS, Tallinn, Estonia) in both relaxed and contracted conditions. MAS was evaluated by the free oscillation technique on a leg-extension dynamometer. These measures were performed before and after the fatiguing intervention. Results A significant decrease in peak torque was observed from pre-fatigue (208.2±47.1 Nm) to post-fatigue (189.3±52.5 Nm) (P −1 – relaxed ; 493.6±71.2 Nm −1 – contracted ) to post-fatigue (454.3±82.8 Nm −1 – relaxed ; 551.3±89.7 Nm −1 – contracted ) (P MS/load supported ) was significantly increased from pre-fatigue (26.4±6.9 Nm −1 ·kg −1 ) to post-fatigue (230.8±6.5 Nm −1 ·kg −1 ) (P −1 ) to post-fatigue (1421.6±445.7 Nm −1 ) (P MAS/load supported ) no significant difference was observed (P=.06). Conclusions It is hypothesized that the observed increase in MS may be a compensatory mechanism to offset the fatigue induced decrease in peak torque and MAS, with the aim of preserving knee joint stability.

This study investigated the effects of dynamic knee extension and flexion fatiguing task on torque and neuromuscular responses in young and older individuals. Eighteen young (8 males; 25.1 ± 3.2 years) and 17 older (8 males; 69.7 ± 3.7 years) volunteered. Following a maximal voluntary isometric contraction test, participants performed a fatiguing task involving 22 maximal isokinetic (concentric) knee extension and flexion contractions at 60°/s, while surface EMG was recorded simultaneously from the knee extensors (KE) and flexors (KF). Fatigue-induced relative torque reductions were similar between age groups for KE (peak torque decrease: 25.15% vs 26.81%); however, KF torque was less affected in older individuals (young vs older peak torque decrease: 27.6% vs 11.5%; p 0.001) and this was associated with greater increase in hamstring EMG amplitude (p 0.001) and hamstrings/quadriceps peak torque ratio (p 0.01). Furthermore, KE was more fatigable than KF only among older individuals (peak torque decrease: 26.8% vs 11.5%; p 0.001). These findings showed that the age-related fatigue induced by a dynamic task was greater for the KE, with greater age-related decline in KE compared to KF.

Glucose-6-phosphate dehydrogenase (G6PD) purified from rabbit brain is composed of two identical subunits of 56 kDa. The enzyme exhibits biphasic pH curve, linear Arrhenius plot and elevated susceptibility to inactivation by metal catalyzed oxidation and thiol binding reagents. 4-Hydroxy-2-nonenal (HNE) is able to inactivate the enzyme after only a few minutes of incubation. Since reactive oxygen species and G6PD-HNE adducts form easily in brain under conditions of oxidative stress, these findings have important implications in the loss of active G6PD molecules in vivo, a process which lowers the antioxidant protection and may be critical for neuron survival.