Tom Timbert

Purpose: To determine whether superimposed local vibration (SLV) increases time to task failure (TTF) during submaximal isometric knee extensor contractions at low and moderate intensities (respectively, 30% and 50% of maximal voluntary isometric contraction, MVIC) and to examine whether the SLV effect differs between sexes. Methods: Fifty-two healthy young adults were assigned to either a 30% or 50% MVIC group ( n = 26 each, 11 women per group). Each group performed a unilateral intermittent isometric knee-extension fatiguing task (15 s contraction/5 s rest) under two randomized conditions (SLV and control, CON), until task failure. Torque and electromyographic (EMG) activity of the knee extensor and flexor muscles were recorded for the entire duration of the task. TTF was defined as the time until torque output dropped more than 10% below the target force. Torque time integral (TTI) was calculated over the TTF. Results: TTF was significantly greater (+9.5 ± 17.3%) in the SLV condition compared with the control ( P < 0.001), independently of contraction intensity (30% vs 50% MVIC, P = 0.901) and sex ( P = 0.183). TTI was greater in SLV than CON (+8.9 ± 17.4%, P < 0.001) with no significant sex or intensity interactions (both P > 0.183). Despite the longer TTF and higher TTI, no difference in EMG during the fatiguing task was observed between conditions ( P > 0.173). Conclusions: SLV enhances time to failure and force production during submaximal intermittent isometric contractions, regardless of sex or intensity. Unchanged EMG between conditions throughout the fatiguing task suggests greater time spent at high EMG levels with SLV, warranting further investigation.

This study investigated the effects of superimposed local vibration (SLV) during a fatiguing intermittent isometric protocol involving high-intensity contractions [70% maximal voluntary isometric contraction (MVIC)]. SLV did not alter the torque-time integral or the duration of exercise before task failure. In addition, neuromuscular fatigue responses evaluated up to 30 min after exercise were comparable between conditions. These findings indicate that intermittent SLV does not enhance the capacity to sustain force or mitigate fatigue during high-intensity isometric exercise in healthy adults.

The prolonged application (>20 min) of local vibration (LV) on muscles or tendons is known to reduce maximal isometric strength. However, the effect of short vibration durations (≤6 min) is still unknown. In fourteen participants, the changes in maximal voluntary isometric contraction (MVIC) were measured after 1, 3, and 6 min of rest (CONT) or local vibration (LV) over the quadricipital tendon (frequency: 100 Hz; amplitude: 0.5 mm). Before and after each condition, the amplitude of the twitch induced by a 100 Hz potentiated electrical doublet (PD_POT); the relative electromyographic activity of the vastus medialis and rectus femoris muscle during the MVIC (RMS_MVIC.M⁻¹); the torque developed 50 ms after the onset of contraction (T₅₀); and the voluntary activation level (VAL) were evaluated. None of the three LV durations significantly changed the MVIC compared with the control condition (p = 0.379). The indices of central (i.e., VAL, T₅₀, RMS_MVIC.M⁻¹) and peripheral (e.g., PD_POT) fatigue were unaffected (p > 0.147). In conclusion, a short-duration LV (≤6 min) on a voluminous muscle group does not impair maximal force production or induce any central or peripherical fatigue.

Prolonged application (> 20 minutes) of LV on muscles or tendons is known to reduce maximal isometric strength. However, the effect of short vibration durations (< 6 minutes) is still unknown. In fourteen participants, the changes in maximal voluntary isometric contraction (MVIC) were measured after 1, 3, and 6 minutes of rest (CONT) or local vibration (LV) over the quadricipital tendon (frequency: 100 Hz; amplitude: 0.5mm). Before and after each condition, the amplitude of the twitch induced by a 100 Hz potentiated electrical doublet (PDPOT), relative electromyographic activity of the vastus medialis and rectus femoris muscle during the MVIC (RMSMVIC.M-1), the torque developed 50 ms after the onset of contraction (T50) and the voluntary activation level (VAL) were evaluated. None of the three LV durations significantly changed MVIC compared with the control condition (p = .379). Indices of central (i.e., VAL, T50, RMSMVIC.M-1) and peripheral (PDPOT) fatigue were unaffected (p > .147). In conclusion, a short duration of LV (<6min) on a voluminous muscle group, does not impair maximal force production nor induce any central or peripherical fatigue.

Body weight support (BWS) and incline running (IR) are commonly used either during rehabilitation or during training separately, with many positive effects on athletes’ performance and rehabilitation. The aim of the present study was to investigate the interaction between bodyweight support and incline running on the electromyographic activity of the triceps surae and compare it to flat running. In eighteen healthy men (age: 20.3 ± 1.2 years, body weight: 70.2 ± 4.8 kg, body height: 179.6 ± 5.4 cm), the changes in electromyographic activity (EMGA) during a 10 min run with BWS (15% or 30% of body weight; in different occasions) and IR at 7%, as well as jumping performance and gait spatiotemporal parameters, were evaluated. A lower Rating of Perceived Exertion and a significant decrease in the size of the Vastus Lateralis (VL) (33.4%), Soleus (SOL) (17%), and Gastrocnemius Lateralis (GL) EMGA (28.5%, p < 0.05) but not in Gastrocnemius Medialis (GM) (10.5%, p > 0.05), was observed during BWS30% at 7% slope compared to flat running. Also, low-frequency fatigue of the quadriceps was induced only after running without BWS on a 7% slope (p = 0.011). No changes were found in jumping performance (p = 0.246) and gait spatiotemporal parameters (p > 0.05) except for flight time (p < 0.006). In conclusion, running with a slope of 7% and 30% of BWS can result in EMG activity comparable to that observed during level running. This method can also be used in prevention and rehabilitation training programs without creating fatigue.

Body weight support (BWS) and incline running (IR) are commonly used either during rehabilitation or during training separately, with many positive effects on athletes’ performance and rehabilitation. The aim of this study is to investigate the effect of BWS and IR. In eighteen healthy men (age: 20.3 ± 1.2 yr, body weight: 70.2 ± 4.8 kg, body height: 179.6 ± 5.4 cm), the changes in electromyographic activity (EMGA) during a 10-min run with BWS (15% or 30% of body weight; in different occasions) and IR at 7%, as well as jumping performance and gait spatiotemporal parameters were evaluated. Lower Rating of Perceived Exertion and a significant decrease in VL (33,4%), SOL (17%), and GL EMGA (28.5%, p < 0.05) but not in GM (10.5%, p > 0.05), were observed during BWS30% at 7% slope compared to flat running. Also, low-frequency fatigue of the quadriceps was induced only after running without BWS at 7% slope (P = 0.011). No changes were found in jumping performance (p = 0.246) and gait spatiotemporal parameters (p > 0.05) except for flight time (p < 0.006). In conclusion, compared to normal flat running, BWS reduces electromyographic activity and fatigue during slope running.