Effects of Weight Cutting on Exercise Performance in Combat Athletes: A Meta-Analysis.

Weight cutting in combat sports is a prevalent practice whereby athletes voluntarily dehydrate themselves via various methods to induce rapid weight loss (RWL) to qualify for a lower weight category than that of their usual training body weight. The intention behind this practice is to regain the lost body mass and compete at a heavier mass than permitted by the designated weight category. The purpose of this study was to quantitatively synthesize the available evidence examining the effects of weight cutting on exercise performance in combat-sport athletes. Following a systematic search of the literature, meta-analyses were performed to compare maximal strength, maximal power, anaerobic capacity, and/or repeated high-intensity-effort performance before rapid weight loss (pre-RWL), immediately following RWL (post-RWL), and 3 to 36 hours after RWL following recovery and rapid weight gain (post-RWG). Overall, exercise performance was unchanged between pre-RWL and post-RWG (g = 0.22; 95% CI, -0.18 to 0.62). Between pre-RWL and post-RWL analyses revealed small reductions in maximal strength and repeated high-intensity-effort performance (g = -0.29; 95% CI, -0.54 to -0.03 and g = -0.37; 95% CI, -0.59 to -0.16, respectively; both P ≤ .03). Qualitative analysis indicates that maximal strength and power remained comparable between post-RWL and post-RWG. These data suggest that weight cutting in combat-sport athletes does not alter short-duration, repeated high-intensity-effort performance; however, there is evidence to suggest that select exercise performance outcomes may decline as a product of RWL. It remains unclear whether these are restored by RWG.

Comparison of energy expenditure and heart rate responses between three commercial group fitness classes.

OBJECTIVES: The objectives of this study were to compare the energy expenditure and heart rate responses between three commercial group fitness classes (group resistance exercise [PUMP]; indoor stationary cycling [RIDE]; and step aerobics [STEP]). DESIGN: One-Way Repeated Measures incorporating a Latin Square Design for class randomisation. METHODS: Ten participants (5 males and 5 females) completed each group fitness class in random order with energy expenditure and heart rate determined using an Actiheart monitor. RESULTS: STEP and RIDE produced significantly (p<0.05) higher average heart rates (HRavg) (85.8±5.1% and 86.4±4.3% of HRmax, respectively) compared to PUMP (73.7±7% of HRmax). HRpeak was also significantly (p<0.05) higher in STEP and RIDE (97.1±4.7% and 95.6±4.5% of HRmax, respectively) when compared with the PUMP class (90±5.9% of HRmax). Total energy expenditure (TEE), both absolute and relative, were significantly (p<0.05) higher for STEP (2101.7±560.2kJ and 0.59±0.07kJkg-1min-1) and RIDE (1880.4±420kJ and 0.58±0.03kJkg-1min-1) when compared with the PUMP class (1385.1±504kJ and 0.36±0.07kJkg-1min-1). CONCLUSIONS: These data suggest that overall exercise intensity and energy expenditure was highly comparable between RIDE and STEP, which suggests these group fitness classes are more effective for developing cardiovascular fitness and assisting with weight management compared with group resistance exercise classes when performed on a regular basis.

Acute effects of a dopamine/norepinephrine reuptake inhibitor on neuromuscular performance following self-paced exercise in cool and hot environments.

Dopamine/norepinephrine (DA/NE) reuptake inhibitors have been used to manipulate the central mechanisms affecting arousal and motivation during exercise. Eight healthy, physically active males performed 30min fixed-intensity cycling at 50% Wmax followed by 30min of self paced time trial (TT) with each section interspersed with a 30 s maximal sprint at 9, 19 and 29min. The DA/NE re-uptake inhibitor administered was bupropion (BUP) versus a placebo (PLA) in either warm (32°C, BUP32 or PLA32) or moderate (20°C; BUP20, PLA20) ambient conditions. Core and skin temperature, heart rate and perceptual responses, neuromuscular and hormonal measures were assessed at multiple times throughout the trials and post exercise. Time trial performance remained unchanged across conditions (12.7-13.1km) although core temperature was elevated in the fixed intensity section of the trials for BUP32 and BUP20 but continued to rise only in BUP32 during the time trial reaching 38.6°C (P<0.05). NE increased in all conditions from pre-exercise with BUP32 values peaking at the end of TT to 1245.3±203.1pg/mL (P<0.05) compared to the other conditions. Neuromuscular responses were similar among conditions although peak force was significantly reduced from pre (262±31N) to post (202±31N, P<0.05) exercise along with contraction duration (22%, P<0.05) in BUP20. We conclude that DA/NE re-uptake inhibitors influenced thermoregulation in the heat but not exercise performance. DA/NE re-uptake inhibitors are likely to act centrally to override the inhibitory signals for the cessation of exercise with these drugs acting peripherally to reduce the twitch characteristics of skeletal muscle in cooler conditions.

The effects of acute versus chronic training status on pacing strategies of older men in a hot, humid environment.

The combined effects of age and training on the regulation of exercise performance may be confounded by the additional challenge of thermoregulation. Thus, the objective of this study was to compare the pacing strategy of older men who have recently completed 12 weeks of exercise training (acute) to men who have been regularly (>3 times/week) training for at least 6 months (chronic) in a hot, humid environment and to observe disparity, if any, between acute and chronic exercise training on thermoregulation. Eleven chronically trained men (OT) completed a familiarisation trial before returning after 7-10 days to repeat the protocol. Similarly, eight untrained men (OU-PRE) were familiarised and repeated the protocol before completing 12 weeks of exercise training. Post-training, the eight acutely trained men (OU-POST) returned to the laboratory for a third trial. All trials were conducted on a cycle ergometer at the same time of the day in a climate controlled chamber with a mean dry bulb temperature and relative humidity of 32.0°C and 68%, respectively. OT consumed more water than OU-POST and OU-PRE (P<0.01) whilst no differences were observed in the OU with training. Voluntary activation of the knee extensors decreased by 11.3% (P<0.05) in the OU-PRE after the cycling time trial. However, the decrease in voluntary activation observed in the OU-POST and OT after the cycling time trial were not significant. The OT maintained a higher power output compared with the OU-POST and OU-PRE except for the last sprint, whilst no significant differences in power output were observed between the OU-PRE and OU-POST. The rate of rise in core temperature was significantly higher in the OT compared with OU-POST (P<0.001) and OU-PRE (P<0.001). With more experience in training, the OT used an alternative hydration strategy compared with the OU-POST and OU-PRE to mitigate the effects of possible exercise hyperthermia, ultimately attaining a higher, but non-critical core temperature at the end of the cycling time trial. Twelve weeks of exercise training may not manifest in improved exercise performance per se, but could translate to improved performance of activities of daily and independent living.

Cerebral responses to innocuous somatic pressure stimulation following aerobic exercise rehabilitation in chronic pain patients: a functional magnetic resonance imaging study.

OBJECTIVE: The purpose of this research was to assess the functional brain activity and perceptual rating of innocuous somatic pressure stimulation before and after exercise rehabilitation in patients with chronic pain. MATERIALS AND METHODS: Eleven chronic pain patients and eight healthy pain-free controls completed 12 weeks of supervised aerobic exercise intervention. Perceptual rating of standardized somatic pressure stimulation (2 kg) on the right anterior mid-thigh and brain responses during functional magnetic resonance imaging (fMRI) were assessed at pre- and postexercise rehabilitation. RESULTS: There was a significant difference in the perceptual rating of innocuous somatic pressure stimulation between the chronic pain and control groups (P=0.02) but no difference following exercise rehabilitation. Whole brain voxel-wise analysis with correction for multiple comparisons revealed trends for differences in fMRI responses between the chronic pain and control groups in the superior temporal gyrus (chronic pain > control, corrected P=0.30), thalamus, and caudate (control > chronic, corrected P=0.23). Repeated measures of the regions of interest (5 mm radius) for blood oxygen level-dependent signal response revealed trend differences for superior temporal gyrus (P=0.06), thalamus (P=0.04), and caudate (P=0.21). Group-by-time interactions revealed trend differences in the caudate (P=0.10) and superior temporal gyrus (P=0.29). CONCLUSION: Augmented perceptual and brain responses to innocuous somatic pressure stimulation were shown in the chronic pain group compared to the control group; however, 12-weeks of exercise rehabilitation did not significantly attenuate these responses.

The effect of double--blind carbohydrate ingestion during 60 km of self-paced exercise in warm ambient conditions.

This study evaluated double blind ingestions of placebo (PLA) versus 6% carbohydrate (CHO) either as capsules (c) or beverage (b) during 60 km self-paced cycling in the heat (32°C and 50% relative humidity). Ten well-trained males (mean ± SD: 26±3 years; 64.5±7.7 kg and 70.7±8.8 ml.kg-1.min-1 maximal oxygen consumption) completed four separate 60 km time trials (TT) punctuated by 1 km sprints (14, 29, 44, 59 km) whilst ingesting either PLAb or PLAc or CHOb or CHOc. The TT was not different among treatments (PLAb 130.2±11.2 min, CHOb 140.5±18.1 min, PLAc 143.1±29.2 min, CHOc 137.3±20.1 min; P>0.05). Effect size (Cohen's d) for time was only moderate when comparing CHOb - PLAb (d = 0.68) and PLAb - PLAc (d = 0.57) whereas all other ES were 'trivial' to 'small'. Mean speed throughout the trial was significantly higher for PLAb only (P<0.05). Power output was only different (P<0.05) between the sprints and low intensity efforts within and across conditions. Core and mean skin temperatures were similar among trials. We conclude that CHO ingestion is of little or no benefit as a beverage compared with placebo during 60 km TT in the heat.

Evidence for reduced neuromuscular function in men with a history of androgen deprivation therapy for prostate cancer.

BACKGROUND: Indices of body composition and muscular strength were compared between men with prostate cancer (PCa) treated with androgen deprivation therapy (ADT) and asymptomatic matched men. METHODS: Nine subjects aged 63-83 years with PCa who received ADT (PCa+ADT; duration 6-180 months) and 11 asymptomatic aged-matched eugonadal men (HM) aged 59-80 years were assessed for prostate-specific antigen (PSA) and total testosterone (TT). Total body non-osseous lean mass (TBLM) and right thigh non-osseous fat-free mass (RTLM) were assessed using dual-energy X-ray absorptiometry. Peak torque of the right knee extensors at 0° s(-1) (ISO) and 60° s(-1) (CON), maximal handgrip strength of the dominant hand (MHS) and whole-body strength (WBS) were assessed. ISO and CON per unit mass of RTLM and MHS and WBS per unit mass of TBLM were calculated. RESULTS: Age, height, mass, body mass index and prostate-specific antigen were comparable between groups (P>0·05), while TT was lower in PCa+ADT (P<0·01). RTLM was similar between groups (P≥0·075). Absolute ISO and CON were lower for PCa+ADT (P<0·01) as were CON per unit of RTLM and ISO per unit of RTLM (P<0·05). Absolute MHS, WBS and MHS per unit of TBLM and WBS per unit of TBLM were lower for PCa+ADT (P<0·01; P<0·05). CONCLUSIONS: Men with PCa who receive ADT experience significant losses in whole-body muscular strength compared with asymptomatic age-matched men, which may impair functional capacity. These losses in muscular strength appear to involve neuromuscular mechanisms that are yet to be identified.

Triphasic multinutrient supplementation during acute resistance exercise improves session volume load and reduces muscle damage in strength-trained athletes.

We hypothesized that triphasic multinutrient supplementation during acute resistance exercise would enhance muscular performance, produce a more favorable anabolic profile, and reduce biochemical markers of muscle damage in strength-trained athletes. Fifteen male strength-trained athletes completed two acute lower-body resistance exercise sessions to fatigue 7 days apart. After a 4-hour fast, participants consumed either a multinutrient supplement (Musashi 1-2-3 Step System, Notting Hill, Australia) (SUPP) or placebo (PLA) beverage preexercise (PRE), during (DUR), and immediately postexercise (IP). Session volume loads were calculated as kilograms × repetitions. Lower-body peak power was measured using unloaded repeated countermovement jumps, and blood samples were collected to assess biochemistry, serum hormones, and muscle damage markers at PRE, DUR, IP, 30 minutes postexercise (P30), and 24 hours postexercise (P24h). The SUPP demonstrated increased glucose concentrations at DUR and IP compared with at PRE (P < .01), whereas PLA demonstrated higher glucose at P30 compared with at PRE (P < .001). Session volume load was higher for SUPP compared with PLA (P < .05). Cortisol increased at DUR, IP, and P30 compared with at PRE in both treatments (P < .05); however, SUPP also displayed lower cortisol at P24h compared with at PRE and PLA (P < .01). The total testosterone response to exercise was higher for PLA compared with SUPP (P < .01); however, total creatine kinase and C-reactive protein responses to exercise were lower for SUPP compared with PLA (P < .05). These data indicate that although triphasic multinutrient supplementation did not produce a more favorable anabolic profile, it improved acute resistance exercise performance while attenuating muscle damage in strength-trained athletes.

Self-paced intermittent-sprint performance and pacing strategies following respective pre-cooling and heating.

This study examined the effects of pre-exercise cooling and heating on neuromuscular function, pacing and intermittent-sprint performance in the heat. Ten male, team sport athletes completed three randomized, counterbalanced conditions including a thermo-neutral environment (CONT), whole body submersion in an ice bath (ICE) and passive heating in a hot environment (HEAT) before 50 min of intermittent-sprint exercise (ISE) in the heat (31 + 1°C). Exercise involved repeated 15 m maximal sprints and self-paced exercise of varying intensities. Performance was measured by sprint times and distance covered during self-paced exercise. Maximal isometric contractions were performed to determine the maximal voluntary torque (MVT), activation (VA) and contractile properties. Physiological measures included heart rate (HR), core (T (core)) and skin (T (skin)) temperatures, capillary blood and perceptual ratings. Mean sprint times were slower during ICE compared to HEAT (P < 0.05). Total distance covered was not different between conditions, but less distance was covered during HEAT in 31-40 min compared to CONT, and 41-50 min compared to ICE (P < 0.05). MVT was reduced post-exercise compared to post-intervention in CONT and HEAT. VA was reduced post-intervention in HEAT compared to CONT and ICE, and post-exercise compared to ICE (P < 0.05). HR, T (core) and T (skin) during exercise were lower in ICE compared to CONT and HEAT (P < 0.05). Sprint times and distance covered were not affected by ICE and HEAT conditions compared to CONT. However, initial sprint performance was slowed by pre-cooling, with improvements following passive heating possibly due to altered contractile properties. Conversely, pre-cooling improved exercise intensities, whilst HEAT resulted in greater declines in muscle recruitment and ensuing distance covered.

Cold water immersion recovery following intermittent-sprint exercise in the heat.

This study examined the effects of cold water immersion (CWI) on recovery of neuromuscular function following simulated team-sport exercise in the heat. Ten male team-sport athletes performed two sessions of a 2 × 30-min intermittent-sprint exercise (ISE) in 32°C and 52% humidity, followed by a 20-min CWI intervention or passive recovery (CONT) in a randomized, crossover design. The ISE involved a 15-m sprint every minute separated by bouts of hard running, jogging and walking. Voluntary and evoked neuromuscular function, ratings of perceived muscle soreness (MS) and blood markers for muscle damage were measured pre- and post-exercise, immediately post-recovery, 2-h and 24-h post-recovery. Measures of core temperature (Tcore), heart rate (HR), capillary blood and perceptions of exertion, thermal strain and thirst were also recorded at the aforementioned time points. Post-exercise maximal voluntary contraction (MVC) and activation (VA) were reduced in both conditions and remained below pre-exercise values for the 24-h recovery (P < 0.05). Increased blood markers of muscle damage were observed post-exercise in both conditions and remained elevated for the 24-h recovery period (P < 0.05). Comparative to CONT, the post-recovery rate of reduction in Tcore, HR and MS was enhanced with CWI whilst increasing MVC and VA (P < 0.05). In contrast, 24-h post-recovery MVC and activation were significantly higher in CONT compared to CWI (P = 0.05). Following exercise in the heat, CWI accelerated the reduction in thermal and cardiovascular load, and improved MVC alongside increased central activation immediately and 2-h post-recovery. However, despite improved acute recovery CWI resulted in an attenuated MVC 24-h post-recovery.

Cold application for neuromuscular recovery following intense lower-body exercise.

This study examined the effects of cold therapy (COLD) on recovery of voluntary and evoked contractile properties following high-intensity, muscle-damaging and fatiguing exercise. Ten resistance-trained males performed 6 × 25 maximal concentric/eccentric muscle contractions of the dominant knee extensors (KE) followed by a 20-min recovery (COLD v control) in a randomized cross-over design. Voluntary and evoked neuromuscular properties of the right KE, ratings of perceived muscle soreness (MS) and pain, and blood markers for muscle damage were measured pre- and post-exercise, and immediately post-recovery, 2, 24 and 48-h post-recovery. Exercise resulted in decrements in voluntary and evoked torque, increased MS and elevated muscle damage markers (p < 0.05). Measures of maximal voluntary contraction (MVC) or voluntary activation (VA) were not significantly enhanced by COLD (p > 0.05). Activation of right KE decreased post-exercise with increased activation of biceps femoris (BF) (p < 0.05). However, no significant differences were evident between conditions of activation of KE and hamstrings at any time point (p > 0.05). No significant differences were observed between conditions for creatine kinase or asparate aminotransferase (p > 0.05). However, perceptual ratings of pain were significantly (p < 0.05) lower following COLD compared to control. In conclusion, following damage to the contractile apparatus, COLD did not significantly hasten the recovery of peripheral contractile trauma. Despite no beneficial effect of COLD on recovery of MVC, perceptions of pain were reduced following COLD.

Early-phase neuromuscular adaptations to high- and low-volume resistance training in untrained young and older women.

We compared early-phase effects between high- and low-volume moderate-intensity resistance training on lean muscle volume, maximal bilateral leg extension strength, maximal isometric torque, normalized maximal bilateral leg extension strength, normalized maximal isometric torque, and muscle recruitment of the right knee extensors in previously untrained young (23.8 ± 3.7 years, range 20-30 years; n = 16) and older women (67.6 ± 6.3 years, range 60-78 years; n = 15). Participants performed either one set or three sets of 10 repetitions for the bilateral leg extension and bilateral leg curl at an intensity of 50-75% of maximal strength 3 days per week for 10 weeks. Main effects were observed over time for all variables (P < 0.05) with increases ranging from 7.1% to 27.8% and effect sizes (Cohen's d) ranging from 0.45 to 1.38. No interactions between age and training volume over time were observed for any variable (P > 0.05). Our results provide a novel contribution to the literature demonstrating that additional neuromuscular adaptation during early-phase moderate-intensity resistance training in previously untrained young and older women may not be elicited through higher-volume training when training loads are matched provided that a minimal volume threshold is attained. These findings may have practical applications for the prescription of short-duration resistance training programmes to enhance muscle strength and achieve hypertrophic and non-hypertrophic adaptations in untrained women.

The effects of compression garments on recovery of muscle performance following high-intensity sprint and plyometric exercise.

This study compared the effects of compression garments on recovery of evoked and voluntary performance following fatiguing exercise. Eleven participants performed 2 sessions separated by 7 days, with and without lower-body compression garments during and 24h post-exercise. Participants performed a 10-min exercise protocol of a 20-m sprint and 10 plyometric bounds every minute. Before, following, 2h and 24h post-exercise, evoked twitch properties of the knee extensors, peak concentric knee extension and flexion force were assessed, with blood samples drawn to measure lactate [La(-)], pH, creatine kinase (CK), aspartate transaminase (AST) and c-reactive protein (C-RP). Heart rate, exertion (RPE) and muscle soreness (MS) measures were obtained pre- and post-exercise. No differences (P=0.50-0.80) and small effect sizes (d<0.3) were present for 20-m sprint (3.59+/-0.22 vs. 3.59+/-0.18s) or bounding performance (17.13+/-1.4 vs. 17.21+/-1.7 m) in garment and control conditions. The decline and recovery in concentric force were not different (P=0.40) between conditions. Full recovery of voluntary performance was observed 2h post-exercise, however, evoked twitch properties remained suppressed 2h post-exercise in both conditions. No differences (P=0.40-0.80, d<0.3) were present between conditions for heart rate, RPE, [La(-)], pH, CK or C-RP. However, 24h post-exercise a smaller change (P=0.08; d=2.5) in AST (23.1+/-3.1 vs. 26.0+/-4.0) and reduced (P=0.01; d=1.1) MS (2.8+/-1.2 vs. 4.5+/-1.4) were present in the garments. In conclusion the effects of compression garments on voluntary performance and recovery were minimal; however, reduced levels of perceived MS were reported following recovery in the garments.

Older adults' perceived changes in physical self-worth associated with resistance training.

Using Sonstroem, Harlow, and Josephs' (1994) expanded version of the Exercise and Self-Esteem Model (EXSEM; Sonstroem & Morgan, 1989), we explored how 9 older adults (6 women and 3 men, aged 65-72 years) involved in a resistance training program experienced and perceived changes in physical self-worth (i.e., improved strength, functional competency, physical condition, and body satisfaction). We conducted three in-depth interviews with each participant over the course of the program. In individual log books, participants recorded the weight lifted and the number of repetitions for each exercise. Our findings showed the course of changes in physical self-perceptions in these older adults and how actual individual changes in strength performance related to perceived changes in important psychological outcomes.

Effect of an acute bout of plyometric exercise on neuromuscular fatigue and recovery in recreational athletes.

Although plyometric training is widely used by sports coaches as a method of improving explosive power in athletes, many prescribe volumes in excess of the National Strength and Conditioning Association recommendations. The purpose of this study was to assess voluntary and evoked muscle characteristics to assess the neuromuscular impact of a high-volume bout of plyometric exercise that was non-exhaustive. Ten athletes who did not have plyometric training experience and were in their competitive season for club-level sport volunteered for the study. After at least 2 days without high-intensity activity, subjects were assessed on maximal twitch torque, time to peak torque, rate of twitch torque development, twitch half-relaxation time, rate of twitch relaxation, and voluntary activation by the interpolated twitch technique before, immediately after, and 2 hours after a high-volume plyometric training program (212 ground contacts). Data were analyzed by repeated-measures analysis of variance and described as mean +/- SD and Cohen d. Statistically significant decrements appeared immediately after the training protocol in the total torque generated by maximal voluntary contractions (p < 0.05, d = -0.51) and twitch (p < 0.01, d = -0.92), rate of twitch torque development (p < 0.01, d = -0.77), and rate of relaxation (p < 0.01, d = -0.73). However, we did not observe any differences that remained statistically different after 2 hours. There were no significant differences observed at any time point in time to peak twitch, half-relaxation time, or voluntary activation. We conclude that high-volume plyometric training results primarily in peripheral fatigue that substantially impairs force and rate of force development. We recommend that coaches carefully monitor the volume of plyometric training sessions to avoid neuromuscular impairments that can result in suboptimal training.

Effect of age on muscle activation and twitch properties during static and dynamic actions.

In this investigation we examined age-associated changes in peak torque, voluntary activation levels, and potentiated twitch properties of the knee extensors during isometric (ISO), shortening (SHO), and lengthening (LEN) actions in 18 young subjects (19-27 years) and 12 elderly subjects (64-77 years). Peak torque was lower for the elderly subjects under the ISO (-31%) and SHO (-28%) conditions (P < 0.05); however, the loss in LEN peak torque in the elderly was less marked (-17%) (P > 0.05). Voluntary activation levels within and between groups were not significantly different and ranged between 96.8% and 98.9% (P > 0.05). Peak twitch torque and some temporal twitch characteristics were altered with age (P < 0.05), but such changes were similar across all muscle actions (P > 0.05). These data suggest that the attenuated reduction in LEN muscle strength associated with age is probably not related to contraction-specific changes in voluntary activation levels or potentiated twitch properties. Muscle Nerve, 2009.

Reliability of the nociceptive flexor reflex (RIII) threshold and association with Pain threshold.

The purpose of this study was to assess the reliability of the RIII reflex threshold and Pain threshold in three repeated trials using electrocutaneous stimuli. Each trial was separated by a mean of 4.3 +/- 2.9 days (between-trials) and included two repeated measurements (within-trial) of the RIII reflex threshold (RIII-T) and the Pain threshold (PT) separated by 20 min. The participants were 14 healthy males (mean age +/- SD, 23.5 +/- 5.3 years). There was a significant difference between the RIII-T and PT. The reliability of the RIII-T and PT shows a between-trials coefficient of variance (CV(SEM)) of 16.1 and 16.9%, respectively. The within-trial CV(SEM) for RIII-T and PT was 5.4 and 4.3%, respectively. There was a significant correlation between the RIII-T threshold and PT. The parallel association and correlation of the RIII-T with the PT suggests that the RIII-T is valid in experimental pain studies under standardised resting conditions.

Comparative effects of resistance training on peak isometric torque, muscle hypertrophy, voluntary activation and surface EMG between young and elderly women.

We compared the effect of a 10-week resistance training program on peak isometric torque, muscle hypertrophy, voluntary activation and electromyogram signal amplitude (EMG) of the knee extensors between young and elderly women. Nine young women (YW; range 20-30 years) and eight elderly women (EW; 64-78 years) performed three sets of ten repetitions at 75% 1 repetition maximum for the bilateral leg extension and bilateral leg curl 3 days per week for 10 weeks. Peak isometric torque, EMG and voluntary activation were assessed before, during, and after the training period, while knee extensor lean muscle cross-sectional area (LCSA) and lean muscle volume (LMV) were assessed before and after the training period only. Similar increases in peak isometric torque (16% and 18%), LCSA (13% and 12%), LMV (10% and 9%) and EMG (19% and 21%) were observed between YW and EW, respectively, at the completion of training (P<0.05), while the increase in voluntary activation in YW (1.9%) and EW (2.1%) was not significant (P>0.05). These findings provide evidence to indicate that participation in regular resistance exercise can have significant neuromuscular benefits in women independent of age. The lack of change in voluntary activation following resistance training in both age groups despite the increase in EMG may be related to differences between measurements in their ability to detect resistance training-induced changes in motor unit activity. However, it is possible that neural adaptation did not occur and that the increase in EMG was due to peripheral adaptations.

Contralateral muscle fatigue in human quadriceps muscle: evidence for a centrally mediated fatigue response and cross-over effect.

The purpose of this investigation was to examine the effects of voluntary muscular fatigue in one lower limb and determine whether a 'cross-over' of fatigue is evident in the contralateral limb. Twenty-eight subjects (13 males and 15 females) performed a series of voluntary and evoked isometric contractions of both the dominant (exercised) and non-dominant (non-exercised) leg extensor muscles, prior to and after a fatigue protocol consisting of a 100-s sustained maximal isometric contraction (MVC) performed by the dominant limb only. Force values and surface electromyography (EMG) from the vastus lateralis muscle were obtained allowing for the determination of twitch and compound action potential (M-wave) values. Maximal twitch tension and peak-to-peak amplitude were significantly decreased after the fatigue test in the dominant limb, as was maximal voluntary force (approximately 65 N reduction), EMG activity (approximately 0.1 mV decrease) and voluntary activation (approximately 17% decline). However, no significant changes were observed in the non-dominant limb with respect to twitch and M-wave properties nor in MVC force. The voluntary activation of the non-dominant limb decreased significantly by 8.7% after the fatigue test, which was performed only on the dominant limb. The results of the present study suggest that the decrease in force production in the exercised limb was primarily related to peripheral fatigue mechanisms, with central fatigue making a lesser contribution. Centrally mediated mechanisms appear to be the sole contributor to fatigue in the non-exercised limb suggesting an anticipatory fatigue response and a 'cross-over' of central fatigue between the exercised and non-exercised contralateral limb.