In team sports, sensorimotor impairments resulting from previous injuries or muscular fatigue have been suggested to be factors contributing to an increased injury risk. Although it has been widely shown that physical fatigue affects static postural sway, it is still questionable as to what extent these adaptations are relevant for dynamic, sports-related situations. The objective of this study was to determine the effects of whole-body and localized fatigue on postural control in stable and unstable conditions. Nineteen male team handball players were assessed in 2 sessions separated by 1 week. Treadmill running and single-leg step-up exercises were used to induce physical fatigue. The main outcome measures were center of pressure (COP) sway velocity during a single-leg stance on a force plate and maximum reach distances of the star excursion balance test (SEBT). The COP sway velocity increased significantly (p < 0.05) after general (+47%) and localized fatigue (+10%). No fatigue effects were found for the SEBT. There were no significant correlations between COP sway velocity and SEBT mean reach in any condition. The results showed that although fatigue affects static postural control, sensorimotor mechanisms responsible for regaining dynamic balance in healthy athletes seem to remain predominantly intact. Thus, our data indicate that the exclusive use of static postural sway measures might not be sufficient to allow conclusive statements regarding sensorimotor control in the noninjured athlete population.

Repeated biopsy sampling from one muscle is necessary to investigate muscular adaptation to different forms of exercise as adaptation is thought to be the result of cumulative effects of transient changes in gene expression in response to single exercise bouts. In a crossover study, we obtained four fine needle biopsies from one vastus lateralis muscle of 11 male subjects (25.9 ± 3.8 yr, 179.2 ± 4.8 cm, 76.5 ± 7.0 kg), taken before (baseline), 1, 4, and 24 h after one bout of squatting exercise performed as conventional squatting or as whole body vibration exercise. To investigate if the repeated biopsy sampling has a confounding effect on the observed changes in gene expression, four fine needle biopsies from one vastus lateralis muscle were also taken from 8 male nonexercising control subjects (24.5 ± 3.7 yr, 180.6 ± 1.2 cm, 81.2 ± 1.6 kg) at the equivalent time points. Using RT-PCR, we observed similar patterns of change in the squatting as well as in the control group for the mRNAs of interleukin 6 (IL-6), IL-6 receptor, insulin-like growth factor 1, p21, phosphofructokinase, and glucose transporter in relation to the baseline biopsy. In conclusion, multiple fine needle biopsies obtained from the same muscle region can per se influence the expression of marker genes induced by an acute bout of resistance exercise.

The purpose of the study was to test the hypothesis that myofiber recruitment is enhanced when whole-body vibration (WBV) is added to squat training. In a randomized cross-over design, 14 recreationally active men were subjected to 2 sessions consisting of 5 sets of 10 squats with external load, performed either on a vibration platform (whole-body vibration squatting [WBVS]) or conventionally without WBV (CON). Electromyographic (EMG) activity of the right vastus lateralis muscle was continuously recorded during WBVS and CON. The integrated EMG values were normalized to the EMG activity recorded during measurement of the maximal voluntary contraction force (MVC) on an isometric leg press at the beginning of each training session. Capillary lactate concentration was determined before and repeatedly after the squatting exercise. Overall mean normalized and integrated EMG (nIEMG) activity during WBVS (62 ± 4% MVC) was significantly (p < 0.001) higher compared with CON (47 ± 2% MVC). There was a tendency for nIEMG to increase during the 5 sets of 10 squats performed as WBVS (p = 0.089), whereas there was a significant (p < 0.001) decrease in nIEMG during CON. Whole-body vibration squatting induced a significantly (p < 0.001) larger increase in capillary lactate than CON (3.03 ± 0.32 vs. 1.60 ± 0.30 mmol · L(-1), p < 0.001). The increased myoelectric activity and the enhanced exercise-induced increase in capillary lactate concentration during WBVS provide evidence for augmented recruitment of muscle tissue when WBV is added to exhaustive squatting exercise.