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Pulmonary oxygen uptake ([Formula: see text]) slowly increases during exercise above the anaerobic threshold, and this increase is called the slow component of [Formula: see text]. The mechanism of the increase in [Formula: see text] is assumed to be due to increasing energy cost associated with increasingly inefficient muscle contraction. We hypothesized that the increase in [Formula: see text] would be accompanied by a constant or increasing rate of accumulation of blood lactate, indicating sustained anaerobic metabolism while [Formula: see text] increased. Ten male subjects performed cycle ergometry for 3, 6, and 9 min at a power output representing 60% of the difference between lactate threshold and maximal [Formula: see text] while [Formula: see text] and blood lactate accumulation were measured. Blood lactate accumulation decreased over time, providing the energy equivalent of (mean ± SD) 1586 ± 265, 855 ± 287, and 431 ± 392 ml of [Formula: see text] during 0-3, 3-6, and 6-9 min of exercise, respectively. As duration progressed, [Formula: see text] supplied 86.3 ± 2.0, 93.6 ± 1.9, and 96.8 ± 2.9% of total energy from 0 to 3, 3 to 6, and 6 to 9 min, respectively, while anaerobic contribution decreased. There was no change in total energy cost after 3 min, except that required by ventilatory muscles for the progressive increase in ventilation. The slow component of [Formula: see text] is accompanied by decreasing anaerobic energy contribution beyond 3 min during heavy exercise.

The purpose of this investigation was to examine the influence of muscle fiber type composition on the patterns of responses for electromyographic (EMG) and mechanomyographic (MMG) amplitude and mean power frequency (MPF) during a fatiguing submaximal isometric muscle action. Five resistance-trained (mean +/- SD age = 23.2 +/- 3.7 yrs) and five aerobically-trained (mean +/- SD age = 32.6 +/- 5.2 yrs) men volunteered to perform a fatiguing, 30-sec submaximal isometric muscle action of the leg extensors at 50% of the maximum voluntary contraction (MVC). Muscle biopsies from the vastus lateralis revealed that the myosin heavy chain (MHC) composition for the resistance-trained subjects was 59.0 +/- 4.2% Type IIa, 0.1 +/- 0.1% Type IIx, and 40.9 +/- 4.3% Type I. The aerobically-trained subjects had 27.4 +/- 7.8% Type IIa, 0.0 +/- 0.0% Type IIx, and 72.6 +/- 7.8% Type I MHC. The patterns of responses and mean values for absolute and normalized EMG amplitude and MPF during the fatiguing muscle action were similar for the resistance-trained and aerobically-trained subjects. The resistance-trained subjects demonstrated relatively stable levels for absolute and normalized MMG amplitude and MPF across time, but the aerobically-trained subjects showed increases in MMG amplitude and decreases in MMG MPE The absolute MMG amplitude and MPF values for the resistance-trained subjects were also greater than those for the aerobi-cally-trained subjects. These findings suggested that unlike surface EMG, MMG may be a useful noninvasive technique for examining fatigue-related differences in muscle fiber type composition.

The central governor model has recently been proposed as a general model to explain the phenomenon of fatigue. It proposes that the subconscious brain regulates power output (pacing strategy) by modulating motor unit recruitment to preserve whole body homoeostasis and prevent catastrophic physiological failure such as rigor. In this model, the word fatigue is redefined from a term that describes an exercise decline in the ability to produce force and power to one of sensation or emotion. The underpinnings of the central governor model are the refutation of what is described variously as peripheral fatigue, limitations models, and the cardiovascular/anaerobic/catastrophe model. This argument centres on the inability of lactic acid models of fatigue to adequately explain fatigue. In this review, it is argued that a variety of peripheral factors other than lactic acid are known to compromise muscle force and power and that these effects may protect against "catastrophe". Further, it is shown that a variety of studies indicate that fatigue induced decreases in performance cannot be adequately explained by the central governor model. Instead, it is suggested that the concept of task dependency, in which the mechanisms of fatigue vary depending on the specific exercise stressor, is a more comprehensive and defensible model of fatigue. This model includes aspects of both central and peripheral contributions to fatigue, and the relative importance of each probably varies with the type of exercise.

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT), the joint angle at PT, mean power output (MP), electromyographic (EMG) amplitude, and mechanomyographic (MMG) amplitude of the vastus lateralis (VL) and rectus femoris (RF) muscles during maximal, voluntary concentric isokinetic leg extensions at 60 and 240 degrees x s(-1) of the stretched and unstretched limbs. Twenty-one volunteers [mean age (SD) 21.5 (1.3) years] performed maximal, voluntary concentric isokinetic leg extensions for the dominant and non-dominant limbs at 60 and 240 degrees x s(-1). Surface EMG (muVrms) and MMG (mVrms) signals were recorded from the VL and RF muscles during the isokinetic tests. PT (Nm), the joint angle at PT, and MP (W) were calculated by a dynamometer. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. PT decreased (P< or =0.05) from pre- to post-stretching for the stretched limb at 60 and 240 degrees x s(-1) and for the unstretched limb at 60 degrees x s(-1). EMG amplitude of the VL and RF also decreased (P< or =0.05) from pre- to post-stretching for the stretched and unstretched limbs. There were no stretching-induced changes (P>0.05) for the joint angle at PT, MP, or MMG amplitude. These findings indicated stretching-induced decreases in force production and muscle activation. The decreases in PT and EMG amplitude for the unstretched limb suggested that the stretching-induced decreases may be due to a central nervous system inhibitory mechanism.

The purpose of the present investigation was to examine the effect of concentric isokinetic leg extension training on the mean power frequency (MPF) of the mechanomyographic (MMG) signal. Twenty-one men were assigned into a training (TRN; n = 12) or control (CTL; n = 9) group. The TRN group performed six sets of leg extensions 3 days per week for 12 weeks at a velocity of 90 degrees /s. All subjects were tested every 4 weeks for peak torque (PT), while MMG was recorded from the vastus lateralis. PT increased, but there was no significant (P > 0.05) change in the MMG MPF over the 12-week training period. These results indicate that MMG MPF, measured from the vastus lateralis, was not sensitive to training-induced increases in leg-extension strength, possibly due to competing influences of hypertrophy on the MMG signal and/or training-induced adaptations in muscles other than the vastus lateralis., (Copyright 2000 John Wiley & Sons, Inc.)

Changes in strength following concentric-only weight training and detraining are poorly understood. The purpose of this investigation was to examine the effects of unilateral concentric leg extension weight training and detraining on joint angle specificity, cross-training, and the bilateral deficit (individual limb strength > bilateral strength/2). Sixteen males volunteered to be subjects for this investigation (concentric training group, N = 8; control group, N = 8). The training group performed 8 weeks of training with the nondominant limb three times per week (3-5 sets X six repetitions), followed by 8 weeks of detraining. These subjects were tested pretraining, posttraining, and following detraining for maximal isometric strength at three joint angles (15, 45, and 75 degrees) in both limbs as well as for the one repetition maximum (1-RM) concentric strength of the trained limb, untrained limb, and bilaterally. The results of this investigation indicated that the effects of the concentric weight training were not joint angle specific as the isometric strength increases occurred at all three joint angles. This effect was found in both limbs, indicating that cross-training occurred. The results of the 1-RM analyses showed that initially there was a bilateral deficit (untrained limb > bilateral, trained limb at pretraining). While the concentric training resulted in increases in 1-RM strength in the trained limb, untrained limb, and bilaterally, differences between bilateral strength and the untrained limb were reversed posttraining and the trained limb values exceeded both the bilateral and untrained limb values. Finally, the effects of detraining were more pronounced for isometric strength vs. 1-RM strength as there was a significant decrease from posttraining in the isometric scores, but the detraining 1-RM values were not significantly decreased from posttraining for either limb or bilaterally.

The purpose of this investigation was to determine the effect of an aerobic training program on physical working capacity at the heart rate threshold (PWCHRT). A total of 19 subjects volunteered for this investigation. The control group (CG) consisted of three females and four males, while the training group (TG) included four females and eight males. All subjects were pretested and posttested for maximal oxygen consumption rate (VO2max) and PWCHRT. The training consisted of riding a cycle ergometer for 30 min at 85% of maximal heart rate (HR) three times per week for 8 weeks. Two univariate (VO2max and PWCHRT) 2 x 2 mixed factorial analyses of variance [group (CG, TG) x time (pretraining, posttraining)] were used to analyze the data. A significant (P < 0.05) group by time interaction for PWCHRT was followed by paired t-tests to analyze the simple main effects. The PWCHRT for the TG increased significantly (P < 0.05) as a result of the training program, whereas no change occurred for the CG. The VO2max did not change significantly for either the TG or the CG. The results of this investigation demonstrate that PWCHRT was sensitive to the effects of an 8-week aerobic training program.

The purposes of this investigation were to examine the effects of unilateral eccentric-only dynamic constant external resistance (DCER) training of the leg extensor muscles on: (a) eccentric DCER strength in the trained and untrained limbs, (b) concentric isokinetic leg extension peak torque-velocity curves in the trained and untrained limbs, and (c) retention of eccentric DCER strength and concentric isokinetic peak torque in the trained and untrained limbs following detraining. Seventeen adult male (X age +/- SD = 24 +/- 3 yr) volunteers comprised training (TR, n = 9) and control (CTL, n = 8) groups. The TR group trained the leg extensor muscles of the nondominant limb with eccentric-only DCER exercise (3 - 5 sets of 6 repetitions at 80% of the eccentric one-repetition maximum [1-RM] load) for eight weeks followed by eight additional weeks of detraining. The CTL group did not train. All subjects were tested pretraining, posttraining, and after detraining for 1-RM unilateral eccentric DCER strength of the leg extensor muscles as well as concentric isokinetic leg extension peak torque at 1.05, 2.09, 3.14, 4.19, and 5.24 rad.s(-1) in both limbs. Mixed factorial ANOVAs, follow-ups, and post-hoc analyses indicated that the training resulted in increased eccentric DCER strength in both the trained (29 %) and untrained (17 %) limbs, but no change in isokinetic peak torque at any of the velocities of contraction in either limb. Furthermore, the training-induced increases in eccentric DCER strength for both limbs were retained across eight weeks of detraining.

The purpose of this study was to examine the effects of unilateral isometric leg extension strength training on the strength and integrated electromyogram (IEMG) of both the trained and untrained limbs at multiple joint angles. A training (TRN) group [nine women; mean (SD) age, 20(1) years] exercised for 6 weeks with isometric leg extensions at 80% of maximal isometric torque. A control (CTL) group [eight women; 21(1) years] did not exercise. The training was performed three times per week on a Cybex II isokinetic dynamometer at a joint angle where the lever arm was 0.79 rad below the horizontal plane. The subjects were tested pre- and posttraining for maximal unilateral isometric torque in both limbs at joint angles of zero, 0.26, 0.79, 1.31, and 1.57 rad below the horizontal plane. Bipolar surface electrodes were used to record the IEMG of the vastus lateralis (VL) and vastus medialis (VM) during the isometric tests. Three univariate (torque, IEMG-VL, and IEMG-VM) four-way (group x time x limb x angle) mixed factorial ANOVAs were used to analyze the data. The results indicated joint angle specificity for isometric torque in the TRN group only, with significant increases in torque at 0.79 (P = 0.0004) and 1.31 (P = 0.0039) rad. No significant increases in torque were found in the untrained limb of the TRN group or in either limb of the CTL group. Similarly, there were no significant changes in IEMG as a result of the training for the VL or VM.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study was to examine the effects of unilateral strength training on the strength and integrated electromyogram (IEMG) of the trained and untrained limbs at several joint angles. A training group [TRN; 4 females and 3 males, age 22 +/- 4 yr (SD)] exercised for 6 wk with isometric leg extensions at 80% of maximal isometric torque. A control group (3 females and 3 males, age 24 +/- 4 yr) did not exercise. The training was performed three times per week at 0.79 rad below the horizontal plane. The subjects were tested at joint angles of 0.00, 0.26, 0.79, 1.31, and 1.57 rad. Bipolar surface electrodes were used to record the IEMG of the vastus lateralis. The results indicated a cross-training effect and joint angle specificity for isometric torque in TRN only, with significant (P < 0.0005) increases in torque (collapsed across limb) at 0.26 (23.3%) and 0.79 (22.3%) rad. There was a dissociation, however, between changes in torque and IEMG with an increase (P < 0.05) in IEMG (collapsed across limb and angle) for TRN. The dissociation between the IEMG and strength changes was possibly due to differential responses to training in the four muscles of the quadriceps femoris.