Nicolas Babault

Reliability of knee extension and flexion measurements using the Con‐Trex isokinetic dynamometer

The aim of this study was to evaluate the reliability of isokinetic and isometric assessments of the knee extensor and the flexor muscle function using the Con‐Trex isokinetic dynamometer. Thirty healthy subjects (15 males, 15 females) were tested and retested 7 days later for maximal strength (isokinetic peak torque, work, power and angle of peak torque as well as isometric maximal voluntary contraction torque and rate of torque development) and fatigue (per cent loss and linear slope of torque and work across a series of 20 contractions). For both the knee extensor and the flexor muscle groups, all strength data – except angle of peak torque – demonstrated moderate‐to‐high reliability, with intraclass correlation coefficients (ICC) higher than 0·86. The highest reliability was observed for concentric peak torque of the knee extensor muscles (ICC = 0·99). Test–retest reliability of fatigue variables was moderate for the knee extensor (ICC range 0·84–0·89) and insufficient‐to‐moderate for the knee flexor muscles (ICC range 0·78–0·81). The more reliable index of muscle fatigue was the linear slope of the decline in work output. These findings establish the reliability of isokinetic and isometric measurements using the Con‐Trex machine.

Electrostimulation training effects on the physical performance of ice hockey players.

PURPOSE The aim of this study was to examine the influence of a short-term electromyostimulation (EMS) training program on the strength of knee extensors, skating, and vertical jump performance of a group of ice hockey players. METHODS Seventeen ice hockey players participated in this study, with nine in the electrostimulated group (ES) and the remaining height as controls (C). EMS sessions consisted of 30 contractions (4-s duration, 85 Hz) and were carried out 3x wk for 3 wk. Isokinetic strength of the knee extensor muscles was determined with a Biodex dynamometer at different eccentric and concentric angular velocities (angular velocities ranging from -120 to 300 degrees .s). Jumping ability was evaluated during squat jump (SJ), countermovement jump (CMJ), drop jump (DJ), and 15 consecutive CMJ (15J). Sprint times for 10- and 30-m skates in specific conditions were measured using an infrared photoelectric system. RESULTS After 3 wk of EMS training, isokinetic torque increased significantly (P<0.05) for ES group in eccentric (-120 and -60 degrees .s) and concentric conditions (60 and 300 degrees .s), whereas vertical jump height decreased significantly (P<0.05) for SJ (-2.9+/-2.4 cm), CMJ (-2.1+/-2.0 cm), and DJ (-1.3+/-1.1 cm). The 10-m skating performance was significantly improved (from 2.18+/-0.20 to 2.07+/-0.09 s, before and after the 3-wk EMS period, respectively; P<0.05). CONCLUSION It was demonstrated that an EMS program of the knee extensors significantly enhanced isokinetic strength (eccentric and for two concentric velocities) and short skating performance of a group of ice hockey players.

EFFECTS OF ELECTROMYOSTIMULATION TRAINING ON MUSCLE STRENGTH AND POWER OF ELITE RUGBY PLAYERS

The present study investigated the influence of a 12-week electromyostimulation (EMS) training program performed by elite rugby players. Twenty-five rugby players participated in the study, 15 in an electrostimulated group and the remaining 10 in a control group. EMS was conducted on the knee extensor, plantar flexor, and gluteus muscles. During the first 6 weeks, training sessions were carried out 3 times a week and during the last 6 weeks, once a week. Iso-kinetic torque of the knee extensors was determined at different eccentric and concentric angular velocities ranging from = 120 to 360°·s-1. Scrummaging and full squat strength, vertical jump height and sprint-running times were also evaluated. After the first 6 weeks of EMS, only the squat strength was significantly improved (+ 8.3 ± 6.5%; p < 0.01). After the 12th week, the −120°·s-1 maximal eccentric, 120 and 240°·s-1 maximal concentric torque (p < 0.05), squat strength (+ 15.0 ± 8.0%; p < 0.001), squat jump (+ 10.0 ± 9.5%; p < 0.01), and drop jump from a 40-cm height (+ 6.6 ± 6.1%; p < 0.05) were significantly improved. No significant change was observed for the control group. A 12-week EMS training program demonstrated beneficial effects on muscle strength and power in elite rugby players on particular tests. However, rugby skills such as scrummaging and sprinting were not enhanced.

Is eccentric exercise-induced torque decrease contraction type dependent?

PURPOSE This study was designed to determine whether torque decrease following an acute eccentric exercise is contraction type dependent. METHODS Ten active males performed an exercise session consisting of five sets of ten maximal eccentric muscle actions of the elbow flexors. Before and immediately after the exercise, maximal voluntary eccentric (-60 degrees.s-1; Ecc60), isometric (0 degrees.s-1; Iso) and concentric (60 degrees.s-1; Con60 and 240 degrees.s-1; Con240) torque were measured. In order to distinguish central from peripheral factors involved in torque decrement, activation level (twitch interpolation technique), myoelectrical activity (RMS) of biceps brachii, as well as electrically evoked M-wave and peak twitch torque (Pt) were recorded. RESULTS The eccentric exercise induced a significant torque reduction (P < 0.01), whatever the muscular contraction type [mean (SD): -22.3 (8.1)% for Ecc60; -20.8 (11.2)% for Iso; -18.5 (6.1)% for Con60 and -12.5 (8.9)% for Con240]. Relative torque decrement was however significantly less for Con240 compared with Ecc60, Iso, and Con60 (P < 0.05). Torque decreases were associated with a reduction of both M-wave amplitude (P < 0.01) and Pt (P < 0.001), probably related to an impairment of the excitation-contraction coupling. Concurrently, activation level was reduced (P < 0.01), therefore indicating the occurrence of central fatigue, as also confirmed by RMS decreases for all the conditions (P < 0.05), except Con240. DISCUSSION An acute eccentric exercise induced a significant voluntary maximal torque reduction during eccentric, isometric, and concentric muscle actions ascribed to both peripheral and central failure of force production capacity. It can be concluded that eccentric exercise-induced torque decrease is not contraction type dependent.

Neuromuscular fatigue induced by a 90-minute soccer game modeling.

Robineau, J, Jouaux, T, Lacroix, M, and Babault, N. Neuromuscular fatigue induced by a 90-minute soccer game modeling. J Strength Cond Res 26(2): 555–562, 2012—This study aimed to quantify neuromuscular fatigue induced by a soccer game. Eight amateur soccer players (age 20.4 ± 1.3 years, mass 70.4 ± 6.9 kg, and height 174.9 ± 5.2 cm) reproduced a 90-minute soccer game modeling composed of two 45-minute periods separated by a 15-minute rest. Torque of quadriceps and hamstring muscle groups associated with electromyography, sprint speed, and vertical jump height was assessed before, at halftime, and immediately after the modeling. Most physical qualities decreased throughout the game with greater decays at match end than at halftime. Contrarily to quadriceps muscles, hamstring torque impairments were not accompanied by electromyographic activity reductions. Squat jump height was reduced at halftime and game end without any change for countermovement jumps. The sprint speed decrease was associated with stride frequency impairments without any change in amplitude and contact time. We concluded on torque production capacity and specific performance impairments during and after soccer games. Neuromuscular fatigue appeared primarily centrally mediated as attested by the reduced quadriceps muscle activity.

Acute effects of 15 min static or contract-relax stretching modalities on plantar flexors neuromuscular properties

The present study aimed to investigate the immediate effects of 15 min static or sub-maximal contract-relax stretching modalities on the neuromuscular properties of plantar flexor muscles. Ten male volunteers were tested before and immediately after 15 min static or contract-relax stretching programs of plantar flexor muscles (20 stretches). Static stretching consisted in 30s stretches to the point of discomfort. For the contract-relax stretching modality, subjects performed 6s sub-maximal isometric plantar flexion before 24s static stretches. Measurements included maximal voluntary isometric torque (MVT) and the corresponding electromyographic activity of soleus (SOL) and medial gastrocnemius (MG) muscles (RMS values), as well as maximal peak torque (Pt) elicited at rest by single supramaximal electrical stimulation of the tibial nerve. After 15 min stretching, significant MVT and SOL RMS decreases were obtained (-6.9+/-11.6% and -6.5+/-15.4%, respectively). No difference was obtained between stretching modalities. Pt remained unchanged after stretching. MG RMS changes were significantly different between stretching modalities (-9.4+/-18.3% and +3.5+/-11.6% after static and contract-relax stretching modalities, respectively). These findings indicated that performing 15 min static or contract-relax stretching had detrimental effects on the torque production capacity of plantar flexor muscles and should be precluded before competition. Mechanisms explaining this alteration seemed to be stretch modality dependent.

Influence of ultra-long-term fatigue on the oxygen cost of two types of locomotion

Abstract The aim of this study was to examine the effects of fatigue induced by a 65-km ultramarathon on the oxygen cost of running (Cr) and cycling (Ccycl). The day before and immediately after the race, a group of nine well-trained male subjects performed two sub-maximal 4-min exercise bouts: one cycling at a power corresponding to 1.5 W · kg−1 body mass on an electromagnetically braked ergometer, and one running at 11 km · h−1 on a flat asphalt roadway. Before oxygen cost determinations, the subjects performed 12 “ankle” jumps at a given frequency that was fixed by an electronic metronome (2.5 Hz). From the non-fatigued to the fatigued condition, there was a significant increase in minute ventilation for both running (P < 0.01) and cycling (P < 0.0001). Significant changes were also found in respiratory exchange ratio both for running (P=0.01) and cycling (P < 0.0001). However, running and cycling differed in that Ccycl increased significantly by [mean (SD)] 24.2 (11.5)% (P < 0.001), suggesting an alteration of muscle efficiency, while Cr did not change with fatigue [186.8 (14.1) mlO2 · kg−1 · km−1 vs 186.8 (18.7) mlO2 · kg−1 · km−1]. In addition, contact times during hopping increased significantly from 0.173 (0.019) ms to 0.194 (0.027) ms (P < 0.01). Analysis of the factors that determine Cr indicate that the subjects modified their movement pattern in order to decrease the mechanical cost of running in such long-term fatigue conditions.

Does electrical stimulation enhance post-exercise performance recovery?

Elite sport requires high-volume and high-intensity training that inevitably induces neuromuscular fatigue detrimental for physical performance. Improving recovery processes is, therefore, fundamental and to this, a wide variety of recovery modalities could be proposed. Among them, neuromuscular electrical stimulation is largely adopted particularly by endurance-type and team sport athletes. This type of solicitation, when used with low stimulation frequencies, induces contractions of short duration and low intensity comparable to active recovery. This might be of interest to favour muscle blood flow and therefore metabolites washout to accelerate recovery kinetics during and after fatiguing exercises, training sessions or competition. However, although electrical stimulation is often used for recovery, limited evidence exists regarding its effects for an improvement of most physiological variables or reduced subjective rating of muscle soreness. Therefore, the main aim of this brief review is to present recent results from the literature to clarify the effectiveness of electrical stimulation as a recovery modality.

Effects of an Electrostimulation Training Program on Strength, Jumping, and Kicking Capacities in Soccer Players

Billot, M, Martin, A, Paizis, C, Cometti, C, and Babault, N. Effects of an electrostimulation training program on strength, jumping, and kicking capacities in soccer players. J Strength Cond Res 24(5): 1407-1413, 2010-The present study investigated the influence of a 5-week electrostimulation (EMS) training program on muscular strength, kicking velocity, sprint, and vertical jump performance in soccer players. Twenty amateur soccer players participated in the study, 10 in the electrostimulated group and the remaining 10 in a control group. Electrostimulation was applied on the quadriceps muscles over 5 weeks. Subjects were tested before, during (wk-3), and after (wk-5) the EMS training program. Maximal voluntary contraction using different contraction mode (i.e., eccentric, concentric, and isometric), vertical jump height, sprint running for 10 m, and ball speed were examined. We observed an increase in isometric and eccentric maximal knee extension torques and also a gain in ball speed performance without run up at wk-3. After 5 weeks of EMS training, eccentric, isometric, and concentric torques and ball speed had significantly improved. It appeared appropriate to conduct EMS training during at least 3 weeks to observe beneficial effects in specific soccer skills such as ball speed.

Postactivation Potentiation in Human Knee Extensors during Dynamic Passive Movements

PURPOSE Postactivation potentiation (PAP), i.e., the increase in twitch torque following a maximal voluntary conditioning contraction, has been shown to depend on muscle contractile conditions (e.g., muscle length). Few studies, however, have investigated the extent of twitch PAP under dynamic conditions in human subjects. Therefore, the aim of the present experiment was to test the twitch PAP during passive dynamic movements following isometric conditioning contractions on nine healthy men. METHODS Maximal twitches were evoked on the knee extensor muscles before and exactly 5 s after a 3-s conditioning maximal voluntary isometric contraction. PAP was determined at a constant joint angle under isometric conditions, during and immediately after passive shortening and lengthening with slow and fast angular velocities (30 and 150 degrees .s). RESULTS Our results indicate a significant PAP increase with increasing shortening angular velocity (34.6 +/- 13.2% and 51.9 +/- 21.1% at 30 degrees .s and 150 degrees .s velocities, respectively), whereas PAP was significantly lower during lengthening (15.2 +/- 15.2%) as compared with isometric conditions (28.5 +/- 18.3%). Similar results were obtained when PAP was determined isometrically but immediately following passive shortening or lengthening (30 degrees .s). CONCLUSION These data indicate that PAP affects dynamic torque production capacity and that PAP is dependent on contractile conditions. Furthermore, the similar extent of PAP during and immediately after passive movements suggests a PAP history dependency. Our results therefore suggest that PAP is recommended more for improving shortening performance than for lengthening.