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Purpose: The contribution of tissue mechanical response to vocal fatigue is poorly understood. This study investigated the fatigue response of vocal fold tissues to large-amplitude vibration exposure at phonatory frequencies, using an ex vivo ovine model. Method: Twelve sheep vocal fold mucosal specimens were subjected to sinusoidal, simple-shear deformation for prolonged cycles, under a large but physiological shear strain (46%) in a frequency range of 100-230 Hz. The duration of shear varied from a critical vibration exposure limit of 1,040 s to 4 times the limit (4,160 s). Tissue viscoelastic response was quantified by the elastic shear modulus (G1), viscous shear modulus (G'), and damping ratio (G'/G'). Results: Distinct response patterns were observed at different frequencies. G' and G' generally decreased with vibration exposure at 100 Hz, whereas they generally increased with vibration exposure at 200 and 230 Hz. Statistically significant differences were found for G' increasing with vibration exposure at 200 Hz and damping ratio decreasing with vibration exposure at 200 Hz. Significant increases with frequency were also found for all viscoelastic functions. Results suggested that the contribution of tissue viscoelastic response to vocal fatigue could be highly frequency dependent. In particular, increases in G' with vibration exposure could lead to high phonation threshold pressures and difficulty sustaining phonation at higher frequencies following prolonged vocalization. Conclusion: These preliminary findings may help us better understand vocal fatigue and recovery and should be corroborated by studies with human vocal fold tissues., Vocal fatigue is frequently experienced by individuals in vocally demanding professions and by individuals with various kinds of voice disorders, and it is often related to the perception of a [...]

In the current study, the effects of troxerutin (TRX) on muscle fatigue and gene expression of Bcl-2 and Bax in the hepatic tissue of rats was investigated. Forty male Wistar rats were randomly divided into 4 groups and designated as control and TRX treatment at 75 (TRX75), 150 (TRX150), and 300 mg/kg per day (TRX300). The treated groups and control group received TRX and water orally for 7 days. After an exhaustive swimming test on the 7th day, all animals were euthanized immediately and several biochemical parameters related to fatigue and gene expression of Bcl-2 and Bax in the hepatic tissue were measured. Our results showed that the exhaustion swimming time in the TRX300 groups significantly increased 1.2-fold compared with the control group (P < 0.001). TRX300 significantly reduced ALT (P Key words: apoptosis, exhaustive exercise, muscle fatigue, oxidative stress, troxerutin. Dans les presents travaux, nous avons etudie l'effet de la troxerutine (TRX) sur la fatigue musculaire et l'expression des genes Bcl-2 et Bax dans le tissu hepatique de rat. Nous avons reparti aleatoirement 40 rats Wistar males dans les quatre groupes suivants: temoin et administration de TRX a 75 (TRX75), 150 (TRX150) et 300 mg/kg par jour (TRX300). Les groupes TRX et placebo ont recu pendant 7 jours de la TRX et de l'eau, respectivement. Le 7e jour, tous les animaux ont ete euthanasies immediatement apres un test de nage menant a l'epuisement, et nous avons mesure plusieurs parametres biochimiques lies a la fatigue et a l'expression des genes Bcl-2 et Bax dans le tissu hepatique. Nos resultats ont montre que dans le groupe TRX300, le temps de nage ecoule avant l'epuisement etait 1,2 fois plus eleve que dans le groupe temoin (resultats statistiquement significatifs : P < 0,001). Dans le groupe TRX300, l'activite de l'ALT diminuait et l'activite hepatique de la SOD augmentait de facons nettement plus marquees que dans le groupe temoin (P < 0,05 et P < 0,01, respectivement). De plus, la TRX entrainait une diminution de l'expression de l'ARNm du gene Bax et une augmentation du rapport Bcl-2/Bax nettement plus marquees que dans le groupe temoin (P < 0,001 dans les deux cas). D'apres nos donnees, la TRX exerce une action anti-apoptotique et hepatoprotectrice a la suite d'un exercice de nage menant a l'epuisement. [Traduit par la Redaction] Mots-cles: apoptose, exercice physique menant a l'epuisement, fatigue musculaire, stress oxydatif, troxerutine., Introduction Regular exercise improves cardiorespiratory function (Babu et al. 2016), enhances athletic performance (McCann and Flanagan 2010) and reduces the risk of developing chronic diseases such as type 2 diabetes, [...]

I know it's a little late in the day for it, but I want to start with breakfast. It was a Sunday in May 1990, final exam week of my [...]

Although it is well known that fatigue can greatly reduce muscle forces, it is not generally included in biomechanical models. The aim of the present study was to develop an electromyographic-driven (EMG-driven) biomechanical model to estimate the contributions of flexor and extensor muscle groups to the net joint moment during a nonisokinetic functional movement (squat exercise) performed in nonfatigued and in fatigued conditions. A methodology that aims at balancing the decreased muscle moment production capacity following fatigue was developed. During an isometric fatigue session, a linear regression was created linking the decrease in force production capacity of the muscle (normalized force/EMG ratio) to the EMG mean frequency. Using the decrease in mean frequency estimated through wavelet transforms between dynamic squats performed before and after the fatigue session as input to the previous linear regression, a coefficient accounting for the presence of fatigue in the quadriceps group was computed. This coefficient was used to constrain the moment production capacity of the fatigued muscle group within an EMG-driven optimization model dedicated to estimate the contributions of the knee flexor and extensor muscle groups to the net joint moment. During squats, our results showed significant increases in the EMG amplitudes with fatigue (+23.27% in average) while the outputs of the EMG-driven model were similar. The modifications of the EMG amplitudes following fatigue were successfully taken into account while estimating the contributions of the flexor and extensor muscle groups to the net joint moment. These results demonstrated that the new procedure was able to estimate the decrease in moment production capacity of the fatigued muscle group. [DOI: 10.1115/1.4001383] Keywords: EMG, biomechanical model, muscle fatigue, muscle force, frequency shift

Skeletal muscle, during periods of exertion, experiences several different fatigue-based changes in contractility, including reductions in force, velocity, power output, and energy usage. The fatigue-induced changes in contractility stem from many different factors, including alterations in the levels of metabolites, oxidative damage, and phosphorylation of the myosin regulatory light chain (RLC). Here, we measured the direct molecular effects of fatigue-like conditions on actomyosin's unloaded sliding velocity using the in vitro motility assay. We examined how changes in ATP, ADP, [P.sub.i], and pH affect the ability of the myosin to translocate actin and whether the effects of each individual molecular species are additive. We found that the primary causes of the reduction in unloaded sliding velocity are increased [ADP] and lowered pH and that the combined effects of the molecular species are nonadditive. Furthermore, since an increase in RLC phosphorylation is often associated with fatigue, we examined the differential effects of myosin RLC phosphorylation and fatigue on actin filament velocity. We found that phosphorylation of the RLC causes a 22% depression in sliding velocity. On the other hand, RLC phosphorylation ameliorates the slowing of velocity under fatigue-like conditions. We also found that phosphorylation of the myosin RLC increases actomyosin affinity for ADP, suggesting a kinetic role for RLC phosphorylation. Furthermore, we showed that ADP binding to skeletal muscle is load dependent, consistent with the existence of a load-dependent isomerization of the ADP bound state. motility assay; RLC; load-dependent kinetics; skeletal muscle doi: 10.1152/ajpregu.00566.2009.

The purpose of this study was to develop and assess the reliability of a repeated anaerobic power cycling test designed to mimic the repeated sprinting nature of the sport of ice hockey. Nineteen female varsity ice hockey players ([bar.x] [+ or -] SD age, height and body mass = 21 [+ or -] 2 yr, 166.6 [+ or -] 6.3 cm and 62.3 [+ or -] 7.3) completed 3 trials of a repeated anaerobic power test on a Monark cycle ergometer on different days. The test consisted of 'all-out' cycling for 5 seconds separated by 10 seconds of low-intensity cycling, repeated 4 times. The relative load factor used for the resistance setting was equal to 0.095 kg per kilogram body mass. There was no significant difference between the peak 5-second power output (PO), mean PO, or the fatigue index (%) among the 3 different trials. The peak 5-second PO was 702.6 [+ or -] 114.8 w and 11.3 [+ or -] 1.1 w x [kg.sup.1], whereas the mean PO across the 4 repeats was 647.1 z 96.3 wand 10.4 [+ or -] 1.0 w x [kg.sup.1] averaged for the 3 different tests. The fatigue index averaged 17.8 [+ or -] 6.5%. The intraclass correlation coefficient for peak 5-second, mean PO, and fatigue index was 0.82, 0.86, and 0.82, respectively. This study reports the methodology of a repeated anaerobic power cycling test that was reliable for the measurement of PO and calculated fatigue index in varsity women ice hockey players and can be used as a laboratory-based assessment of repeated anaerobic fitness. KEY WORDS power output, sprinting, fatigue, ergometry, fitness

Isometric contractions, such as occurring during rock climbing, occlude blood flow to the active musculature. The ability to maximize forearm blood flow between such contractions is a likely determinant of intermittent handgrip performance. This study aimed to test the hypothesis that intermittent isometric handgrip performance is improved by 2 common active recovery strategies suggested to increase muscle blood flow. On 6 separate occasions, 9 trained indoor rock climbers and 9 untrained participants undertook a fatiguing, intermittent, isometric handgrip exercise bout consisting of sets of 6 contractions (approximately 33% of maximal voluntary contraction [MVC] force), each 3-second long separated by a 1-second rest. Between sets, participants were allowed 9-second recovery performing passive rest, 'shaking out' (vigorously shaking the hand), or grasping a handgrip vibration machine, each with or without forearm occlusion. Performance was assessed by pre-and post-exercise MVC trials and a 20-contraction post-exercise handgrip time trial ([TT.sub.20]). Trained climbers exhibited significantly greater handgrip MVC force and intermittent exercise capacity than untrained (p < 0.01). There was no effect of recovery strategy on any measure (p > 0.05). Trained climbers were more affected by occlusion than untrained in MVC (p < 0.05) and [TT.sub.20] (p < 0.01). Shaking out and low-frequency vibration are unlikely to affect rock climbing performance, it is recommended that rock climbers and their coaches focus on optimizing body position rather than compromising body position to allow for shaking out. KEY WORDS shaking out, vibration, rock climbing, blood flow, fatigue

The purpose of the present study was to investigate the effect of a tennis training session on the balance performance of young tennis players. The study was conducted on 36 elite tennis players (age 14 [+ or -] 2 years; body mass 55 [+ or -] 6 kg; body height 165 [+ or -] 6 cm; mean [+ or -] SD) participating in the national young tennis championship. Balance performance was assessed before and immediately after a tennis training session (pre-training and post-training, respectively). The balance assessment was performed with 2 different balance boards and the Biodex Stability System. In addition, dynamometric measurements of peak isokinetic moment in the knee flexors and extensors were performed pre and post tennis training session, to quantify the degree of muscle fatigue induced by the tennis training session. One-way analysis of variance with repeated measures was used to test for differences in balance performance and in isokinetic performance between pre and post tennis training session. The data analysis revealed no significant differences (p > 0.05) in balance performance, whereas there were significant differences in knee joint moment production between pre and post tennis training measures. Although the tennis training session of the present study had no significant effect (p > 0.05) on any of the balance performance indicators examined, there was a decline in balance performance, which suggests that different level of fatigue for an extended period (games) will have greater effect on balance performance. It is suggested that a tennis-specific balance exercise program should be included in the tennis training session. KEY WORDS elite tennis players, coordination, training fatigue

J Strength Cond Res 24(1): 251-256, 2010--Reportedly, muscle fatigue in older individuals is greater, less than, or similar to young individuals, potentially because of differences in muscle groups studied, type of contraction, continuous vs. intermittent contractions, exercise duration, duty cycle, and contraction speed. During a single set of isokinetic mode knee extensions, muscle fatigue is similar between older and younger individuals. However, repeated sets may favor the more oxidative nature of muscle from older adults and may be necessary to reveal age-associated enhanced fatigue resistance. The purpose of this investigation was to compare muscular fatigue induced by repeated sets of intermittent isokinetic mode knee extensions in older and younger males. Nineteen older (mean [+ or -] SD) (66 [+ or -] 6 yr) and 16 younger (21 [+ or -] 2 yr) men completed 5 sets of 30 isokinetic mode knee extensions at 180 degrees/second. In the analysis of absolute fatigue, both groups significantly decreased torque production during each set, with young men having significantly higher torque production during all 5 sets. Relative fatigue was significantly greater in young participants during sets 2 through 5 (old vs. young: set 2:1 7.1 vs. 26.6%; set 3:25.5 vs. 39.7%; set 4:28.1 vs. 45.1%; set 5:29.3 vs. 46.4%; overall relative fatigue: old 22.2%; young 38.1%). These data indicate enhanced fatigue resistance in older men, which was revealed using repeated sets of intermittent contractions. Resistance to muscle fatigue is only one component of healthy aging muscle, and perhaps exercise interventions targeted toward prevention of falls in the elderly should focus on improved muscle power rather than fatigability/sustainability of contractions. KEY WORDS sarcopenia, muscle endurance, elderly, isokinetic, aging, exercise, Biodex

The purpose of the present study was to examine the oxygen uptake ([Vo.sub.2]), heart rate (HR), and ratings of perceived exertion (RPE [OMNI-Leg 0-10]) responses during continuous 1-hour cycle ergometer rides at the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (physical working capacity at the oxygen consumption threshold). Eight subjects (mean age [+ or -] SD = 23 [+ or -] 3.2 years) performed a maximal test to exhaustion for the determination of [Vo.sub.2]peak and ventilatory threshold (VT). The subjects also performed 4 randomly ordered 8-minute workbouts at different power outputs (ranging from 84 to 245 W) to determine the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and a continuous 1 -hour cycle ergometer ride at the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] during which [Vo.sub.2], HR, and RPE data were collected every 2 minutes. The [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (114 [+ or -] 39 W) and VT (133 [+ or -] 44 W) were not significantly different and occurred at 56 and 63% [Vo.sub.2]peak, respectively. Linear regression showed that the slope coefficients for the [Vo.sub.2], HR, and RPE vs. time relationships for the continuous 1-hour workbouts were significantly greater than zero. Furthermore, a t-test about a single mean indicated that the mean slope coefficient for the HR vs. time relationship was significantly greater than 0.1 bpm x [min.sup.-1] (the rate of increase in HR that can be maintained for an 8-hour day). The results of this study indicated that [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] could be maintained for an extended period. However, the maximal power output associated with steady state [Vo.sub.2], HR, and RPE responses was overestimated. The mean increase in 402 during the continuous 1-hour ride was 270 mL, which suggested that the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] may demarcate the moderate from heavy exercise domains. The mean HR slope coefficient of 0.3 bpm x [min.sup.-1] indicated that the power output at the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] could likely be maintained for greater than 2 hours. KEY WORDS physical work capacity, fatigue threshold, ventilatory threshold, endurance exercise

Erculi, F and Supej, M. Impact of fatigue on the position of the release arm and shoulder girdle over a longer shooting distance for an elite basketball player. J Strength Cond Res 23(3): 1029-1036, 2009--The purpose of this case study is to establish how a gradual increase in fatigue affects the position of the arms and shoulders during a long shot in a basketball game. For this purpose, Primoz Brezec, an elite National Basketball Association player, performed a total of 7 series of 20 shots from a distance of 7.24 m. The subject performed a special basketball motor task between individual series' of shots. The fatigue gradually increased with each motor task, and in the meantime, the subject's heart rate (HR) and blood lactate concentration (LA) were measured. The height of each jump during the shot at the basket was measured, and all shots were recorded using a system of 3 digital cameras operating at a frequency of 50 Hz. Thereafter, a kinematic analysis was applied to calculate the height of the shoulder and wrist of the release arm, as well as the elbow and upper arm angles, with regard to the vertical line. The study results reveal statistically significant differences (p < 0.05) between the series of throws in all measured variables. The heights of the shoulder axis and of the wrist both decrease with growing fatigue. This is particularly apparent in the last series, i.e., in the conditions of maximum fatigue (HR= 96% [HR.sub.peak]; LA = 9.7 mmol x [L.sup.-1]). Both measured angles decrease drastically in the last series of shots. The results of the study clearly demonstrate changes in the shooting technique as a consequence of moderate and, in particular, heavy fatigue. The findings also suggest the need for basketball coaches and basketball conditioning coaches to include moderate- and high-intensity exercise in their shooting practice sessions. KEY WORDS endurance, jump shot, technique

Purpose: The objective was to identify acoustic correlates of laryngeal muscle fatigue in conditions of vocal effort. Method: In a previous study, a technique of electromyography (EMG) served to define [...]

The purpose of this study was to determine whether exhaustion modifies the stiffness characteristics, as defined in the spring-mass model, during track running. We also investigated whether stiffer runners are also the most economical. Nine well-trained runners performed an exhaustive exercise over 2000 meters on an indoor track. This exhaustive exercise was preceded by a warm-up and was followed by an active recovery. Throughout all the exercises, the energy cost of running ([C.sub.r]) was measured. Vertical and leg stiffness was measured with a force plate ([K.sub.vert] and [K.sub.leg], respectively) integrated into the track. The results show that [C.sub.r] increases significantly after the 2000-meter run (0.192 [+ or -] 0.006 to 0.21 7 [+ or -] 0.013 mL*[kg.sup.-1]*[m.sup.-1]). However, [K.sub.vert] and [K.sub.leg] remained constant (32.52 [+ or -] 6.42 to 32.59 [+ or -] 5.48 and 11.12 [+ or -] 2.76 to 11.14 [+ or -] 2.48 kN*[m.sup.-1], respectively). An inverse correlation was observed between [C.sub.r] and [K.sub.leg], but only during the 2000-meter exercise (r = 0.67; p [less than or equal to] 0.05). During the warm-up or the recovery, [C.sub.r] and [K.sub.leg], were not correlated (r = 0.354; p = 0.82 and r = 0.21 ; p = 0.59, respectively). On track, exhaustion induced by a 2000-meter run has no effect on [K.sub.leg] or [K.sub.vert]. The inverse correlation was only observed between [C.sub.r] and [K.sub.leg] during the 2000-meter run and not before or after the exercise, suggesting that the stiffness of the runner may be not associated with the Cr. KEY WORDS fatigue, stiffness, oxygen uptake, biomechanics

The present study examined muscle adaptations and alterations in work capacity in endurance-trained runners after a change from endurance to sprint training. Fifteen runners were assigned to either a sprint training (ST, n = 8) or a control (CON, n = 7) group. ST replaced their normal training by 30-s sprint runs three to four times a week, whereas CON continued the endurance training (~45 km/wk). After the 4-wk sprint period, the expression of the muscle [Na.sup.+]-[K.sup.+] pump [[alpha].sub.1]-subunit and [Na.sup.+]/[H.sup.+]exchanger isoform 1 was 29 and 30% higher (P < 0.05), respectively. Furthermore, plasma [K.sup.+] concentration was reduced (P < 0.05) during repeated intense running. In ST, performance in a 30-s sprint test, Yo-Yo intermittent recovery test, and two supramaximal exhaustive runs was improved (P < 0.05) by 7, 19, 27, and 19%, respectively, after the sprint training period, whereas pulmonary maximum oxygen uptake and 10-k time were unchanged. No changes in CON were observed. The present data suggest a role of the [Na.sup.+]-[K.sup.+] pump in the control of [K.sup.+] homeostasis and in the development of fatigue during repeated high-intensity exercise. Furthermore, performance during intense exercise can be improved and endurance performance maintained even with a reduction in training volume if the intensity of training is very high. fatigue; pH; lactate; performance; sodium-potassium-chloride 1 protein cotransporters

The mechanisms responsible for the inhibition of shortening velocity that occurs during muscle fatigue have not been completely elucidated. Phosphorylation of the myosin regulatory light chain (RLC) occurs during heavy use; however, previous reports on its role in affecting velocity have been equivocal. To further understand the process of fatigue, we varied the levels of myosin RLC phosphorylation (from 10 to >50%) and the concentrations of protons (from pH 7 to 6.2) and phosphate (from 5 to 30 mM), all of which change during fatigue. We measured the mechanics of permeable rabbit psoas fibers at a temperature closer to physiological (30[degrees]C), using a temperature jump protocol to briefly activate the fibers at the higher temperature to preserve sarcomere homogeneity. Although lowered pH alone had an effect on velocity, it was the three factors together, i.e., high phosphorylation, low pH, and high phosphate, that acted synergistically to inhibit fiber velocity by ~40%. Our data demonstrate that in conditions that simulate physiological muscle fatigue, myosin phosphorylation does contribute to the inhibition of contraction velocity of fully activated fast muscle fibers. mechanics; myosin; pH

Locomotor muscle fatigue, defined as an exercise-induced reduction in maximal voluntary force, occurs during prolonged exercise, but its effects on cardiorespiratory responses and exercise performance are unknown. In this investigation, a significant reduction in locomotor muscle force (-18%, P < 0.05) was isolated from the metabolic stress usually associated with fatiguing exercise using a 100-drop-jumps protocol consisting of one jump every 20 s from a 40-cm-high platform. The effect of this treatment on time to exhaustion during high-intensity constant-power cycling was measured in study 1 (n = 10). In study 2 (n = 14), test duration (871 [+ or -] 280 s) was matched between fatigue and control condition (rest). In study 1, locomotor muscle fatigue caused a significant curtailment in time to exhaustion (636 [+ or -] 278 s) compared with control (750 [+ or -] 281 s) (P = 0.003) and increased cardiac output. Breathing frequency was significantly higher in the fatigue condition in both studies despite similar oxygen consumption and blood lactate accumulation. In study 2, high-intensity cycling did not induce further fatigue to eccentrically-fatigued locomotor muscles. In both studies, there was a significant increase in heart rate in the fatigue condition, and perceived exertion was significantly increased in stud), 2 compared with control. These results suggest that locomotor muscle fatigue has a significant influence on cardiorespiratory responses and exercise performance during high-intensity cycling independently from metabolic stress. These effects seem to be mediated by the increased central motor command and perception of effort required to exercise with weaker locomotor muscles. perception of effort; central motor command; cardiorespiratory regulation; motivation; endurance

During exercise, defects in calcium ([Ca.sup.2+]) release have been proposed to impair muscle function. Here, we show that during exercise in mice and humans, the major [Ca.sup.2+] release channel required for excitationcontraction coupling (ECC) in skeletal muscle, the ryanodine receptor (RyR1), is progressively PKA-hyperphosphorylated, S-nitrosylated, and depleted of the phosphodiesterase PDE4D3 and the RyR1 stabilizing subunit calstabin1 (FKBP12), resulting in 'leaky' channels that cause decreased exercise tolerance in mice. Mice with skeletal musclespecific calstabin1 deletion or PDE4D deficiency exhibited significantly impaired exercise capacity. A small molecule ($107) that prevents depletion of calstabin1 from the RyR1 complex improved force generation and exercise capacity, reduced [Ca.sup.2+]-dependent neutral protease calpain activity and plasma creatine kinase levels. Taken together, these data suggest a possible mechanism by which [Ca.sup.2+] leak via calstabin1-depleted RyR1 channels leads to defective [Ca.sup.2+] signaling, muscle damage, and impaired exercise capacity. muscle fatigue | calcium channel | calstabin | exitation-contraction coupling | rycals

The purpose of the present study was to use ratings of perceived exertion (RPE) from the Borg (6-20) and OMNI-Leg (0-10) scales to determine the Physical Working Capacity at the Borg and OMNI thresholds ([PWC.sub.BORG] and [PWC.sub.OMNI]). [PWC.sub.BORG] and [PW.subC.oMNI] were compared with other fatigue thresholds determined from the measurement of heart rate (the Physical Working Capacity at the Heart Rate Threshold: [PWC.sub.HRT]), and oxygen consumption (the Physical Working Capacity at the Oxygen Consumption Threshold, [MATHEMATICAL NOT REPRODUCIBLE IN ASCII.]), as well as the ventilatory threshold (VT). Fifteen men and women volunteers (mean age [+ or -] SD = 22 [+ or -] 1 years) performed an incremental test to exhaustion on an electronically braked ergometer for the determination of V[O.sub.2 peak] and VT. The subjects also performed 4 randomly ordered workbouts to exhaustion at different power outputs (ranging from 60 to 206W) for the determination of [PWC.sub.BORG], [PWC.sub.OMNI], [PWC.sub.HRT], and [MATHEMATICAL EXPRESSION NOR REPRODUCIBLE IN ASCII.] The results indicated that there were no significant mean differences among the fatigue thresholds: [PWC.sub.BORG] (mean [+ or -] SD = 133 [+ or -] 37W; 67 [+ or -] 8% of V[O.sub.2 peak]), [PWC.sub.OMNI] (137 [+ or -] 44W; 68 [+ or -] 9% of V[O.sub.2] peak), [PW.sub.CHRT] (135 [+ or -] 36W; 68 [+ or -] 8% of V[O.sub.2 peak]), [MATHEMATICAL EXPRESSION NOR REPRODUCIBLE IN ASCCI.],(145 [+ or -] 41W; 72 [+ or -] 7% of V[O.sub.2 peak]) and VT (131 [+ or -] 45W; 66 [+ or -] 8% of V[O.sub.2 peak]). The results of this study indicated that the mathematical model used to estimate [PW.sub.CHRT] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.], can be applied to ratings of perceived exertion to determine [PWC.sub.BORG] and [PWC.sub.OMNI] during cycle ergometry. Salient features of the [PWC.sub.BORG] and [PWC.sub.OMNI] tests are that they are simple to administer and require the use of only an RPE scale, a stopwatch, and a cycle ergometer. Furthermore, the power outputs at the [PWC.sub.BORG] and [PWC.sub.OMNI] may be useful to estimate the VT noninvasively and without the need for expired gas analysis. KEY WORDS fatigue threshold, Borg scale, OMNI-leg scale

The purpose of this study was to compare squat strength gains and volume components when resting 2 minutes vs. 4 minutes between sets over multiple mesocycles. After the first squat 1 repetition maximum, 15 trained men were matched and randomly assigned to either a 2-minute (n = 7) or a 4-minute (n = 8) rest interval group. Each group performed the same training program, with the only difference being the length of the rest interval between sets. Subjects performed two squat workouts per week; one was labeled as Heavy and the other was labeled as Light. The squat workouts varied in the intensity, number of sets, and repetitions performed per set in a nonlinear periodized manner throughout each mesocycle. Differences in strength gains and volume components (the load utilized per set, the repetitions performed per set, the intensity per set, and the volume performed per workout) were compared between groups. Both groups demonstrated large strength gains; however, these differences were not significant between groups (P = 0.47). During all mesocycles, the 4-minute group demonstrated significantly higher total volumes for the Heavy workouts (P < 0.05). The findings of the present study indicate that large squat strength gains can be achieved with a minimum of 2 minutes' rest between sets, and little additional gains are derived from resting 4 minutes between sets. Therefore, athletes attempting to achieve specific volume goals may need longer rest intervals initially but may later adapt so that shorter rest intervals can be utilized without excessive fatigue, leaving additional time to focus on other conditioning priorities. KEY WORDS recovery, repetitions, fatigue, sets, intensity

The aim of the present study was to analyze the association between number of working hours, the level of perceived physical strain, work-home interface and musculoskeletal pain and fatigue among women and men employed in the public sector. Cross-sectional data from 1,180 employees (86% women) in 49 public workplaces in 2002-2003 were analyzed. Odds ratios (OR) with 95% confidence intervals (CIs) were used as measures of the associations. The analyses showed differences as well as similarities between women and men. Overall the women reported higher levels of perceived physical strain relative to total workload. A high level of physical strain was strongly associated with musculoskeletal pain and fatigue. Nevertheless, no detrimental effects were observed on health of high total working hours which indicates that a large number of total working hours might be balanced by accompanying multiple roles or many responsibilities and therefore not be generally regarded as risk factors for ill health. doi:10.1300/J013v47n01_02 KEYWORDS. Gender, physical strain, work hours, paid work, unpaid work, work-home interface

Respiratory muscle fatigue develops during exhaustive exercise and can limit exercise performance. Respiratory muscle training, in turn, can increase exercise performance. We investigated whether respiratory muscle endurance training (RMT) reduces exercise-induced inspiratory and expiratory muscle fatigue. Twenty-one healthy, male volunteers performed twenty 30-min sessions of either normocapnic hyperpnoea (n = 13) or sham training (CON, n = 8) over 4-5 wk. Before and alter training, subjects performed a constant-load cycling test at 85% maximal power output to exhaustion ([PRE.sub.EXH], [POST.sub.EXH]). A further posttraining test was stopped at the pretraining duration ([POST.sub.ISO]) i.e., isotime. Before and after cycling, transdiaphragmatic pressure was measured during cervical magnetic stimulation to assess diaphragm contractility, and gastric pressure was measured during thoracic magnetic stimulation to assess abdominal muscle contractility. Overall, RMT did not reduce respiratory muscle fatigue. However, in subjects who developed >10% of diaphragm or abdominal muscle fatigue in [PRE.sub.EXH], fatigue was significantly reduced after RMT in [POST.sub.ISO] (inspiratory: -17 [+ or -] 6% vs. -9 [+ or -] 10%, P = 0.038, n = 9; abdominal: -19 [+ or -] 10% vs. -11 [+ or -] 11%, P = 0.038, n = 9), while sham training had no significant effect. Similarly, cycling endurance in [POST.sub.EXH] did not improve after RMT (P = 0.071), while a significant improvement was seen in the subgroup with > 10% of diaphragm fatigue after [PRE.sub.EXH] (P = 0.017), but not in the sham training group (P = 0.674). However, changes in cycling endurance did not correlate with changes in respiratory muscle fatigue. In conclusion, RMT decreased the development of respiratory muscle fatigue during intensive exercise, but this change did not seem to improve cycling endurance. inspiratory muscles; expiratory muscles; endurance; magnetic nerve stimulation

The aim of this study was to investigate the concepts of electromyographic (EMG) threshold (EMGT) by integrated EMG (iEMG) signals and neuromuscular fatigue threshold (NMFT) concepts in trained male athletes. Nine competitive national-level male rowers (21.8 [+ or -] 4.4 years; 186.2 [+ or -] 4.6 cm; 79.6 [+ or -] 8.4 kg) took part in this investigation. Subjects were asked to participate in the graded exercise test to volitional exhaustion and 500-, 1,000-, and 2,000-m all-out rowing ergometer tests on a rowing ergometer. During all tests, oxygen consumption parameters, average power, and iEMG of the musculus vastus lateralis were recorded. The second ventilatory threshold (248.9 [+ or -] 26.67 W) and EMGT (258.89 [+ or -] 27.13 W) were not significantly different but were significantly lower than the NMFT (302.25 [+ or -] 45.10 W). During 1,000- and 2,000-m all-out distances, [Vo.sub.2] increased during the first minute and then leveled on a plateau with a slight decrease at the end of the exercise. Vastus lateralis activity showed a slight increase during all distances that was accompanied by a remarkable increase towards the end of the distance. All measured threshold values were significantly correlated (r > 0.70; p < 0.05) to the rowing ergometer performance characteristics. It was concluded that EMGT is closely related to the aerobic-anaerobic transition phase, because NMFT represents the local fatigue accumulation in the muscle. NMFT indicates the performance capacity of the muscles; therefore, it helps coaches to better predict top athletes' performance. KEY WORDS. aerobic-anaerobic transition, muscle fatigue, rowers

McLester et al. (2003) proposed a practical protocol to determine optimal recovery times between resistance training workouts. For this protocol to be useful, it must be stable. The purpose of this study was to investigate the stability of that protocol. College-aged resistance trained men (n = 10) performed 3 sets to volitional failure using a 10-repetition maximum load for 6 exercises. Recovery was evaluated on 4 occasions by the number of repetitions performed for each individual exercise after recovery periods of 48, 72, 96, and 120 hours in counterbalanced order. To evaluate stability, this procedure was performed twice. The number of repetitions after each recovery interval were compared with initial baseline performances. A priori, adequate stability was defined as 70% of the participants achieving similar recovery duration on both trials. Pooled repetitions over all 6 exercises indicated that 80% of participants returned to baseline strength levels after the same recovery duration for both trials. However, when individual muscle group repetition performance was evaluated, stability varied from 20 to 70%. Variability in rest, nutrition, prior activity, and other factors probably induced instability in individual strength measures, but not sufficiently to influence the aggregate results. Some muscle groups may have greater sensitivity to variations in ecological factors such as these. We believe that the tested protocol may be useful in establishing recovery times for multimuscle group workouts, but not stable enough to be useful in establishing recovery times for individual muscle groups. KEY WORDS. weight lifting, fatigue, performance

To examine the influence of muscle fatigue on center of pressure displacement during quiet standing using quantitative and fractal analyses, 12 healthy young men and women did the exercise stress test on the triceps surae muscle until fatigued. Subjects were measured for body stability for 60 sec. before and after the exercise. Quantitative analysis showed that center-of-pressure parameters for distance, velocity, amplitude distribution, and mean vector length of sway in the anterior/posterior direction changed significantly after muscle fatigue but not on the periodic parameters. This result suggested that quantitative analysis may identify the effects of muscle fatigue on the parameters that show displacement in the anterior/posterior direction of center of pressure. Fractal analysis indicated the value of critical point coordinates increased after muscle fatigue. This analysis can clarify the fundamental postural control strategy and time-series characteristics of postural sway which cannot be identified by spectral analysis.