Angelo N. Belcastro

Changes in Calpain Activity, Muscle Structure, and Function after Eccentric Exercise

PURPOSE The aim of this study was to investigate changes in muscle function, muscle structure, and calpain activity after high-force eccentric exercise. METHODS Eleven healthy males performed 300 maximal voluntary eccentric actions with knee extensors in one leg. Maximal force-generating capacity was measured before exercise and regularly during the next 7 d. Biopsies from musculus vastus lateralis were taken in both control and exercised legs 0.5, 4, 8, 24, 96, and 168 h after exercise for evaluation of myofibrillar structure, extracellular matrix proteins, and calpain activity. RESULTS In the exercised leg, peak torque was reduced by 47 +/- 5% during exercise and was still 22 +/- 5% lower than baseline 4 d after the exercise. Calpain activity was three times higher in the exercised leg compared with the control leg 30 min after exercise. Myofibrillar disruptions were observed in 36 +/- 6% of all fibers in exercised muscle and in 2 +/- 1% of fibers in control muscle. The individual reductions in peak torque correlated with the proportion of fibers with myofibrillar disruptions (r = 0.89). The increase in calpain activity was not correlated to the proportion of fibers with myofibrillar disruptions. Nevertheless, the characteristics of the myofibrillar disruptions mimicked calpain-mediated degradation of myofibrils. Tenascin-C and the N-terminal propeptide of procollagen type III showed increased staining intensity on cross-sections 4-7 d after the exercise. CONCLUSIONS Myofibrillar disruptions seem to be a main cause for the long-lasting reduction in force-generating capacity after high-force eccentric exercise. The increase in calpain activity, but the lack of a relationship between calpain activity and the amount of muscle damage, suggests multiple roles of calpain in the damage and repair process.

Metabolic responses to prolonged work during treadmill and water immersion running

The primary aim of this study was to compare the physiological responses to prolonged treadmill (TM) and water immersion to the neck (WI) running at threshold intensity. Ten endurance runners performed TM and WI running VO2max tests. Subjects completed submaximal performance tests at ventilatory threshold (Tvent) intensities under TM and WI conditions and responses at 15 and 42 minutes examined. VO2 was lower in WI (p<0.05) at maximal effort and Tvent. The Tvent VO2 intensities interpolated from the TM and WI VO2max tests were performed in both TM (i.e., TM@TM(tvent),TM@WI(tvent), corresponding to 77.6 and 71.3% respectively of TM VO2max) and WI conditions (i.e., WI@TM(tvent), WI@WI(tvent), corresponding to 85.5% and 78.2% respectively of WI VO2max). Each of the dependent variables was analyzed using a 3-way repeated measures ANOVA (2 conditions X 2 exercise intensities X 7 time points during exercise). VO2max values were significantly lower in the WI (52.4(5.1) ml.kg(-1) min(-1)) versus TM (59.7(6.5) ml.kg(-1) min(-1)) condition. VO2 during submaximal tests were similar during the TM and WI conditions. HR and [BLa] responses to exercise at and above WI(tvent) were similar during short-term exercise, but values tended to be lower during prolonged exercise in the WI condition. There were no statistical differences in VE responses in the 2 conditions, however as with HR and [BLa] an upward trend was noted with TM exercise over the 42 minute duration of the tests. RPE at WI(tvent) was similar for TM and WI exercise sessions, however, RPE at TM(tvent) was higher during WI compared to TM running. Cardiovascular drift was observed during prolonged TM but not WI running. Results suggest differences in metabolic responses to prolonged submaximal exercise in WI, however it can be used effectively for cross training.

Effect of manipulation of plasma lactate on integrated EMG during cycling.

This investigation was undertaken to record electromyographic activity of the vastus lateralis muscle during incremental cycling exercise and to determine whether it would be sensitive to altered dynamics of plasma lactate increases seen with intense exercise. Trained cyclists (N = 6) performed two progressive, stepwise exercise tests (23.5 W.min-1) to fatigue on a cycle ergometer at 90 rpm. One of the exercise tests was preceded by arm ergometer exercise in an attempt to elevate the circulating plasma lactate levels prior to starting the criterion exercise test. The starting mean plasma lactate values were 4.59 and 26.69 mmol lactate.-1 for the two exercise sessions. Cardiorespiratory values did not differ significantly between exercise sessions completed in the absence and presence of increased circulating plasma lactate. The no-arm trial (i.e., nonelevated plasma lactate condition) was associated with a plasma lactate inflection point (Tlac) at 72.6% VO2max. Previous arm exercise elevated the lactate such that during the criterion exercise plasma lactate values were decreasing with increasing power output at lower exercise intensities. As exercise intensity increased lactate values also increased beginning at a power output of about 76% VO2 max. Mean per cycle integrated EMG (CIEMG) increased linearly with increased power output in both exercise sessions. The slopes of the EMG-power output curve were not significantly different (P less than 0.05). There were no inflection points in these curves. The absence of an inflection point show that surface EMG does not provide an indication of Tlac.