Serge S. Colson

Optimal whole-body vibration settings for muscle strength and power enhancement in human knee extensors.

This study compared the effects of 6-week whole-body vibration (WBV) training programs with different frequency and peak-to-peak displacement settings on knee extensor muscle strength and power. The underlying mechanisms of the expected gains were also investigated. Thirty-two physically active male subjects were randomly assigned to a high-frequency/high peak-to-peak displacement group (HH; n=12), a low-frequency/low peak-to-peak displacement group (LL; n=10) or a sham training group (SHAM; n=10). Maximal voluntary isometric, concentric and eccentric torque of the knee extensors, maximal voluntary isometric torque of the knee flexors, jump performance, voluntary muscle activation, and contractile properties of the knee extensors were assessed before and after the training period. Significant improvement in knee extensor eccentric voluntary torque (P<0.01), knee flexor isometric voluntary torque (P<0.05), and jump performance (P<0.05) was observed only for HH group. Regardless of the group, knee extensor muscle contractile properties (P<0.05) were enhanced. No modification was observed for voluntary muscle activation or electrical activity of agonist and antagonist muscles. We concluded that high-frequency/high peak-to-peak displacement was the most effective vibration setting to enhance knee extensor muscle strength and jump performance during a 6-week WBV training program and that these improvements were not mediated by central neural adaptations.

Effects of a physical activity program on postural stability in older people

Background and aims: The objective of this non-randomized study was to determine the influence of a specific physical activity program on the postural stability of older people. Methods: Seventy-four subjects (72.4±0.7 yrs) participated in an individualized three-month physical activity program designed to improve posture, balance and mobility — the PBM program. Sessions were held twice weekly. Postural stability was assessed using a force platform, subjects being in static and dynamic conditions, and with open and closed eyes. Changes in stabilometric parameters (Sway area, ML mean, AP mean, Total length, ML length and AP length) of the intervention group were compared to those of 14 control subjects (71.8±1.5 years). Results: A two-way analysis of variance with repeated measures did not show any significant post-program change in postural stability in the hard floor condition. In contrast, Sway area (p<0.0005), Total length (p<0.001) and AP length (p<0.01) were significantly reduced after the training program in the foam floor condition, with open and closed eyes. In addition, in the mediolateral axis condition and with closed eyes, AP length in the intervention group was significantly reduced (p<0.01, and in the antero-posterior axis condition with both open and closed eyes, Sway area (p<0.0005), Total length (p<0.0005) and AP length (p<0.05) decreased significantly. Conclusions: As shown by the results in the foam floor and dynamic conditions, our individualized physical activity program improved the postural stability of older people when the standing position was challenged. However, the lack of significant results for the hard floor condition suggests that three months is not sufficient to improve static balance. The PBM physical activity program can be used for balance training in older people, but further studies are required to determine the time needed to effect improvements in static balance in this population.

Whole-body vibration training effects on the physical performance of basketball players.

Colson, SS, Pensini, M, Espinosa, J, Garrandes, F, and Legros, P. Whole-body vibration training effects on the physical performance of basketball players. J Strength Cond Res 24(4): 999-1006, 2010-The aim of this study was to investigate the influence of 4 weeks of whole-body vibration training added to the conventional training of basketball players. Eighteen competitive basketball players (13 ♂, 5 ♀, 18-24 years old) were randomly assigned to a whole-body vibration group (WBVG, n = 10; 7 ♂ and 3 ♀) or a control group (CG, n = 8; 6 ♂ and 2 ♀). During the 4-week period, all subjects maintained their conventional basketball training program. The members of WBVG were additionally trained 3 times a week for 20 minutes on a vibration platform (10 unloaded static lower limb exercises, 40-Hz, 4-mm, Silverplate®). Testing was performed before and after the 4-week period and comprised strength assessment, vertical jump performance, and a 10-m sprint test. The maximal voluntary isometric strength of the knee extensors significantly increased (p < 0.001) after vibration training, as did squat jump (SJ) height (p < 0.05), whereas performance of the countermovement jump, drop jump, 30-second rebound jump, and 10-m sprint remained unchanged. The results of the present study indicated that a 4-week whole-body vibration training program added to the conventional training of basketball players during the preseason is an effective short-term stimulus to enhance knee extensor strength and slightly SJ performance.

Effects of electromyostimulation versus voluntary isometric training on elbow flexor muscle strength

The purpose of this study was to determine whether 7 weeks of standardized (same number and duration of repetitions, sets and rest strictly identical) electromyostimulation training of the elbow flexor muscles would induce strength gains equivalent to those of voluntary isometric training in isometric, eccentric and concentric contractions. Twenty-five males were randomly assigned to an electromyostimulated group (EMS, n=9), a voluntary isometric group (VOL, n=8), or a control group (CON, n=8). Maximal voluntary isometric, eccentric and concentric strength, electromyographic (EMG) activity of the biceps and triceps brachii muscles, elbow flexor muscle activation (twitch interpolation technique) and contractile properties were assessed before and after the training period. The main findings were that the isometric torque gains of EMS were greater than those of VOL after the training period (P<0.01) and that the eccentric and concentric torque gains were equivalent. In both groups, we observed that the mechanical twitch (Pt) was increased (P<0.05) and that torque improvements were not mediated by neural adaptations. Considering the respective intensities of the training programs (i.e., submaximal contractions for EMS versus maximal for VOL), it can be concluded that electromyostimulation training would be more efficient than voluntary isometric training to improve both isometric and dynamic strength.

Time course of the cross-over effect of fatigue on the contralateral muscle after unilateral exercise.

We investigated the cross-over effect of muscle fatigue and its time course on the non-exercising contralateral limb (NEL) after unilateral fatiguing contractions of the ipsilateral exercising limb (EL). For this purpose, 15 males performed two bouts of 100-second maximal isometric knee extensions with the exercising limb, and neuromuscular function of both the EL and NEL was assessed before (PRE), after a first fatiguing exercise (MID) and after a second fatiguing exercise (POST). Maximal voluntary isometric torque production declined in the EL after the first bout of exercise (−9.6%; p<0.001) while in the NEL, the decrease occurred after the second bout of exercise (−10.6%; p<0.001). At MID, torque decline of the EL was strictly associated to an alteration of the mechanical twitch properties evoked by neurostimulation of the femoral nerve (i.e., peak twitch torque, maximal rate of twitch development). According to these markers, we suggest that peripheral fatigue occurred. At POST, after the second bout of exercise, the voluntary activation level of the knee extensor muscles was altered from PRE (−9.1%; p<0.001), indicating an overall central failure in both the EL and NEL. These findings indicate that two bouts of unilateral fatiguing exercise were needed to induce a cross-over effect of muscle fatigue on the non-exercising contralateral limb. Differential adjustments of the motor pathway (peripheral fatigue vs. central fatigue) might contribute to the respective torque decline in the EL and the NEL. Given that our unilateral fatiguing exercise induced immediate maximal torque reduction in the EL and postponed the loss of torque production in the NEL, it is also concluded that the time course of muscle fatigue differed between limbs.

Neuromuscular Electrical Stimulation Training: A Safe and Effective Treatment for Facioscapulohumeral Muscular Dystrophy Patients

OBJECTIVE To investigate the feasibility, safety, and effectiveness of neuromuscular electrical stimulation (NMES) strength training in facioscapulohumeral muscular dystrophy (FSHD) patients. DESIGN Uncontrolled before-after trial. SETTING Neuromuscular disease center in a university hospital and a private-practice physical therapy office. PARTICIPANTS FSHD patients (N=9; 3 women, 6 men; age 55.2+/-10.4y) clinically characterized by shoulder girdle and quadriceps femoris muscle weakness. INTERVENTIONS Patients underwent 5 months of strength training with NMES bilaterally applied to the deltoideus, trapezius transversalis, vastus lateralis, and vastus medialis muscles for five 20-minute sessions per week. MAIN OUTCOME MEASURES Plasma creatine kinase (CK) activity; scores for pain and fatigue on visual analog scales (VAS), manual muscle testing (MMT), maximal voluntary isometric contraction (MVIC), 6-minute walking tests (6MWT), and self-reported changes in daily living activities. RESULTS NMES strength training was well tolerated (CK activity and pain and fatigue scores on VAS were not modified). Most of the muscle functions (shoulder flexion and extension and knee extension) assessed by MMT were significantly increased. MVIC of shoulder flexion and abduction and the 6MWT distance were also improved. CONCLUSIONS In FSHD, NMES strength training appears to be safe with positive effects on muscle function, strength, and capacity for daily activities.

Pushing to the limits: The dynamics of cognitive control during exhausting exercise

This study aimed at investigating concurrent changes in cognitive control and cerebral oxygenation (Cox) during steady intense exercise to volitional exhaustion. Fifteen participants were monitored using prefrontal near-infrared spectroscopy and electromyography of the thumb muscles during the completion of an Eriksen flanker task completed either at rest (control condition) or while cycling at a strenuous intensity until exhaustion (exercise condition). Two time windows were matched between the conditions to distinguish a potential exercise-induced evolutive cognitive effect: an initial period and a terminal period. In the initial period, Cox remained unaltered and, contrary to theoretical predictions, exercise did not induce any deficit in selective response inhibition. Rather, the drop-off of the delta curve as reaction time lengthened suggested enhanced efficiency of cognitive processes in the first part of the exercise bout. Shortly before exhaustion, Cox values were severely reduced - though not characteristic of a hypofrontality state - while no sign of deficit in selective response inhibition was observed. Despite this, individuals susceptibility to making fast impulsive errors increased and less efficient online correction of incorrect activation was observed near exhaustion. A negative correlation between Cox values and error rate was observed and is discussed in terms of cerebral resources redistribution.

Relationship Between Lower Limb Muscle Activity and Platform Acceleration During Whole-Body Vibration Exercise

Abstract Lienhard, K, Vienneau, J, Nigg, S, Meste, O, Colson, SS, and Nigg, BM. Relationship between lower limb muscle activity and platform acceleration during whole-body vibration exercise. J Strength Cond Res 29(10): 2844–2853, 2015—The purpose of this study was to identify the influence of different magnitudes and directions of the vibration platform acceleration on surface electromyography (sEMG) during whole-body vibration (WBV) exercises. Therefore, a WBV platform was used that delivers vertical vibrations by a side-alternating mode, horizontal vibrations by a circular mode, and vibrations in all 3 planes by a dual mode. Surface electromyography signals of selected lower limb muscles were measured in 30 individuals while they performed a static squat on a vibration platform. The WBV trials included 2 side-alternating trials (Side-L: 6 Hz, 2.5 mm; Side-H: 16 Hz, 4 mm), 2 circular trials (Circ-L: 14 Hz, 0.8 mm; Circ-H: 43 Hz, 0.8 mm), and 4 dual-mode trials that were the combinations of the single-mode trials (Side-L/Circ-L, Side-L/Circ-H, Side-H/Circ-L, Side-H/Circ-H). Furthermore, control trials without vibration were assessed, and 3-dimensional platform acceleration was quantified during the vibration. Significant increases in the root mean square of the sEMG (sEMGRMS) compared with the control trial were found in most muscles for Side-L/Circ-H (+17 to +63%, p ⩽ 0.05), Side-H/Circ-L (+7 to +227%, p ⩽ 0.05), and Side-H/Circ-H (+21 to +207%, p < 0.01) and in the lower leg muscles for Side-H (+35 to +138%, p ⩽ 0.05). Furthermore, only the vertical platform acceleration showed a linear relationship (r = 0.970, p < 0.001) with the averaged sEMGRMS of the lower limb muscles. Significant increases in sEMGRMS were found with a vertical acceleration threshold of 18 m·s−2 and higher. The present results emphasize that WBV exercises should be performed on a platform that induces vertical accelerations of 18 m·s−2 and higher.

Lower limbs power and stiffness after whole-body vibration.

The interest in whole-body vibration (WBV) for the enhancement of neuromuscular performance has received considerable attention. However, scientific evidence supporting the optimal prescription of WBV settings is lacking. This study investigated the acute effect of WBV combining high frequency/high peak-to-peak displacement (HH) or low frequency/low peak-to-peak displacement (LL) vs. sham intervention (SHAM) on lower limb muscle power and stiffness. A total of 223 volunteers were randomly assigned to either the HH, LL or SHAM group. Countermovement jump (CMJ) height, maximal and average power, maximal and average lower limbs stiffness obtained during a hopping test were recorded before and after the respective intervention. After the intervention, the HH group showed an increase of 4.64% in CMJ height (p<0.001) whereas the values of both the LL and SHAM groups did not change. In addition, maximal and average power of the lower limbs were significantly increased in all groups (p<0.001; 10.89% and 12.82%, respectively) while no effect on lower limbs stiffness was observed. Our data show that high frequency combined with high peak-to-peak displacement is the most optimal WBV setting for CMJ height enhancement. Further investigation should be undertaken to ascertain the effectiveness of WBV on lower limbs stiffness.

Compression Garments, Muscle Contractile Function, and Economy in Trail Runners

BACKGROUND Physiological mechanisms behind the use of compression garments (CGs) during off-road running are unknown. PURPOSE To investigate the influence of wearing CGs vs conventional running clothing (CON) on muscle contractile function and running economy before and after short-distance trail running. METHODS Knee-extensor neuromuscular function and running economy assessed from two 5-min treadmill runs (11 and 14 km/h) were evaluated before and after an 18.6-km short-distance trail run in 12 trained athletes wearing either CGs (stocking + short-tight) or CON. Quadriceps neuromuscular function was assessed from mechanical and EMG recording after maximal percutaneous electrical femoral-nerve stimulations (single-twitch doublets at 10 [Db10] and 100 Hz [Db100] delivered at rest and during maximal quadriceps voluntary contraction [MVC]). RESULTS Running economy (in mL O2 · km-1 · kg-1) increased after trail running independent of the clothing condition and treadmill speeds (P < .001). Similarly, MVC decreased after CON and CGs conditions (-11% and -13%, respectively, P < .001). For both clothing conditions, a significant decrease in quadriceps voluntary activation, Db10, Db100, and the low-to-high frequency doublet ratio were observed after trail running (time effect, all P < .01), without any changes in rectus femoris maximal M-wave. CONCLUSIONS Wearing CGs does not reduce physiological alterations induced during short-distance trail running. Further studies should determine whether higher intensity of compression pressure during exercises of longer duration may be effective to induce any physiological benefits in experienced trail runners.