Reduced elbow extension torque during vibrations.

Impact sports and vibration platforms trigger vibrations within soft tissues and the skeleton. Although the long-term effects of vibrations on the body have been studied extensively, the acute effects of vibrations are little understood. This study determined the influence of acute vibrations at different frequencies and elbow angles on maximal isometric elbow extension torque and muscle activity. Vibrations were generated by a pneumatic vibrator attached to the lever of a dynamometer, and were applied on the forearm of 15 healthy female subjects. The subjects were instructed to push maximally against the lever at three different elbow angles, while extension torque and muscle activity were quantified and compared between vibration and non-vibration (control) conditions. A change in vibration frequency had no significant effects on torque and muscle activity although vibrations in general decreased the maximal extension torque relative to the control by 1.8% (±5.7%, p>0.05), 7.4% (±7.9%, p<0.01), and 5.0% (±8.2%, p<0.01) at elbow angles of 60°, 90°, and 120°, respectively. Electromyographic activity increased significantly between ∼30% and 40% in both triceps and biceps with vibrations. It is speculated that a similar increase in muscle activity between agonist and antagonist, in combination with an unequal increase in muscle moment arms about the elbow joint, limit the maximal extension torque during exposure to vibrations. This study showed that maximal extension torque decreased during vibration exposure while muscle activity increased and suggests that vibrations may be counterproductive during activities requiring maximal strength but potentially beneficial for strength training.

Effects of compression on muscle tissue oxygenation at the onset of exercise.

The effects of compression on gastrocnemius medialis muscle oxygenation and hemodynamics during a short-term dynamic exercise was investigated in a sample of 15 male subjects (mean ± SD; age 25.8 ± 4.9 years; mass 70.6 ± 4.3 kg). Elastic compression sleeves were used to apply multiple levels of compression to the calf muscles during exercise, and noncompressive garments were used for the control condition. Tissue hemoglobin oxygen saturation was measured as the relative "tissue oxygen index" (TOI) with a near-infrared spectrometer. The recovery of TOI during exercise was determined from the slope of oxygenation recovery in a nonoccluded situation. The TOI recovery rate during the first 2 minutes of the exercise was 24% higher (p = 0.042) for the compression condition than for the control condition. A significant correlation (r = 0.61, p = 0.012) between the level of compression and the tissue oxygenation recovery during exercise was observed. Muscle energy use was determined from the rate of decline of TOI immediately upon arterial occlusion during early exercise. Muscle energy use measured during the occluded situation was not significantly influenced by compression. Based on these results, it was concluded that compression induced changes in tissue blood flow and perfusion appear to result in improved oxygenation during short-term exercise. Assuming that increased muscle oxygen availability positively influences performance, compression of muscles may enhance performance especially in sports that require repeated short bouts of exercise.

Effects of vibrations on gastrocnemius medialis tissue oxygenation.

PURPOSE: Whole-body vibrations are known to affect muscle activity and tissue oxygenation, but some energetic aspects are still poorly understood. This study investigates the effects of whole-body vibration on gastrocnemius muscle oxygen utilization rate and tissue oxygenation dynamics during exercise. METHODS: The effects of vibration on gastrocnemius medialis muscle oxygenation were investigated during a dynamic exercise on a sample of 16 active male subjects (age = 26.3 ± 5.1 yr, mass = 71.2 ± 4.8 kg (mean ± SD)). Both arterially occluded (AO) and nonoccluded (N/O) conditions were investigated. Tissue oxygenation was monitored with a near-infrared spectrometer. Oxygen utilization rate and tissue oxygenation recovery were computed as the slopes of the regression line of the oxygenation decay and recovery, respectively. A fast Fourier transform (FFT) was used to determine the frequency spectrum of the oxygen saturation data. EMG activity was monitored using bipolar EMG electrodes. A windowed root mean square analysis was used to monitor the amplitude of the EMG signal. RESULTS: A statistically significant increase of 15% (P < 0.05) in oxygen utilization rate was found for the vibration condition in the AO leg but not in the N/O leg. The oxygenation recovery rate for the vibration condition was 34% higher (P < 0.05) than that for the control condition. A low-frequency periodic oscillation (T ≈ 10 s) in the tissue oxygenation data was determined from the FFT spectrum. A statistically significant decrease in the oscillation frequency was noticed for the vibration condition compared with the control. CONCLUSIONS: Vibrations increased the oxygen utilization rate during a dynamic exercise. The oxygenation recovery rate increased with vibrations. The low-frequency oscillation of the oxygenation was attributed to the periodic changes in tissue blood flow, and this seems to be influenced by vibrations.

Quantification of soft-tissue vibrations in running: accelerometry versus high-speed motion capture.

Soft-tissue vibrations can be used to quantify selected properties of human tissue and their response to impact. Vibrations are typically quantified using high-speed motion capture or accelerometry. The aim of this study was to compare the amplitude and frequency of soft-tissue vibrations during running when quantified by highspeed motion capture and accelerometry simultaneously. This study showed: (a) The estimated measurement errors for amplitude and frequency were of the same order of magnitude for both techniques. (b) There were no significant differences in the mean peak frequencies and peak amplitudes measured by the two methods. (c) The video method showed an inability to capture high frequency information. This study has shown that a tradeoff has to be made between the accuracy in amplitude and frequency when these methods are employed to quantify soft tissue vibrations in running.