The effects of eccentric contraction on myofibrillar proteins in rat skeletal muscle.

The present study investigated the effects of eccentric muscle contractions (ECC) on the content of myofibrillar proteins (my-proteins) and the catalytic activity of myofibrillar ATPase (my-ATPase) in skeletal muscles. Rat extensor digitorum longus and tibialis anterior muscles were exposed to 200-repeated ECC or isometric contractions (ISC) and used for measures of force output and for biochemical analyses, respectively. Whereas in ISC-treated muscles, full restoration of tetanic force was attained after 2 days of recovery, force developed by ECC-treated muscles remained depressed (P < 0.05) after 6 days. The total my-protein content and the relative content of myosin heavy chain (MHC) in total my-proteins were unaltered during 4 days of recovery after ECC, but fell (P < 0.05) to 55.9 and 63.4% after 6 days of recovery, respectively. my-ATPase activity expressed on a my-protein weight basis was unaltered immediately after ECC. However, it decreased (P < 0.05) to 75.3, 45.3, and 49.3% after 2, 4 and 6 days of recovery, respectively. Total maximal calpain activity measured at 5 mM Ca(2+) was significantly augmented (P < 0.05) after 2 days of recovery, reaching a level of threefold higher after 6 days. These alterations were specific for ECC and not observed for ISC. These results suggest that depressions in my-ATPase activity contribute to ECC-induced decreases in force and power which can take a number of days to recover.

Assessment of short-distance breaststroke swimming performance with critical velocity.

For high-velocity running or swimming, the relationship between velocity (v) and its sustainable duration (t) can be described by a hyperbolic relationship: (v - Vcrit)·t = D', where Vcrit is termed critical velocity, and D' is defined as a curvature constant of the hyperbolic curve. The purposes of this study were to examine whether the Vcrit could be applied to evaluate short-distance breaststroke swimming performance and to evaluate the relative contribution of D' in short-distance swimming performance. Eleven male swimmers performed a series of time trials corresponding to 75, 100, and 150-m in an indoor 50-m swimming pool. The observed records were calculated into average velocities of each event to determine Vcrit and D'. After the determination of Vcrit and D', all subjects performed 50-m time trial on another day. A maximal anaerobic power test using cycle ergometer was also performed in the laboratory. The average velocity of the 50-m time trial significantly correlated with the obtained Vcrit, but not with D'. D' was significantly correlated with the residual error, calculated from the regression analysis for the relationship between Vcrit and the average velocities of 50-m time trial. A cluster analysis showed that most of the subjects were classified as Vcrit dependency when performing 50-m time trial. Those results indicated that Vcrit could be applied to evaluate short-distance swimming performance, and it determined around 80% of the short-distance breaststroke swimming performance. Key PointsFor high-velocity running or swimming, the relationship between velocity (v) and its sustainable duration (t) can be described by a hyperbolic relationship: (v - Vcrit)·t = D', where Vcrit is termed critical velocity, and D' is defined as a curvature constant of the hyperbolic curve. The D' contributed only around 20% of the breaststroke swimming performance even in a short-distance event.Critical velocity determined around 80% of 50-m breaststroke swimming performance, and it could be a useful tool for evaluating short-distance swimming performance.Most of the swimmers showed characteristics for critical velocity dependent physical fitness even in short-distance swimming event.

Effects of priming exercise intensity on the dynamic linearity of the pulmonary VO(2) response during heavy exercise.

Prior heavy-intensity exercise facilitates the pulmonary oxygen uptake ( VO(2)) response during subsequent exercise, such that its kinetics returns towards first-order. To better understand this "priming" phenomenon, we investigated the effect of priming exercise, over a range of intensities, on the VO(2) response to heavy-intensity cycle ergometry at a work rate of Delta50% [halfway between lactate threshold (LT) and VO(2max)]. Eight subjects performed two consecutive 6-min bouts separated by 6 min at 20 W. The first bout was each of: no warm-up control (CON), sub-lactate threshold (LT) at 80% of LT, and three supra-LT conditions (Delta20%, Delta40%, and Delta60%). The VO(2) response during the subsequent bout was evaluated using the "effective" time constant (tau'), and the VO(2) difference between minutes 3 and 6 (Delta VO(2(6-3))). The goodness-of-fit, indicative of "first-order" kinetics, was determined by the residual profile, and the mean square of errors (MSEr). The heart rate and blood lactate concentration ([La]r) just prior to the second bout were also measured. Compared with CON, tau' and Delta VO(2(6-3)) were significantly reduced following all supra-LT priming bouts, while the goodness-of-fit was significantly improved following Delta40% exercise. Delta VO(2(6-3)) and [La]r were negatively correlated ( P<0.05), unlike HR. In conclusion, prior exercise just above, but not below, LT facilitated the VO(2) response in a threshold-like manner. Supra-LT priming exercise influenced the VO(2) response allowing it to return to within as little as 12% from first-order (compared to approximately 50% in CON). The associated increases in circulating lactate and/or related factors seem to be centrally involved in this phenomenon.