Julien Duclay

Behavior of fascicles and the myotendinous junction of human medial gastrocnemius following eccentric strength training.

This study is the first in which measurements of thickness, fascicle angle and length, and tendon elongation were combined to examine the impact of eccentric strength training on both muscle architecture and tendinous structures. Eighteen healthy male subjects were divided into an eccentric strength training group (n = 10) and a control group (n = 8). The training program consisted of 18 sessions of eccentric exercises over a 7‐week period. All subjects were tested at baseline and after the last training session. Using ultrasound imaging, the fascicle angle and length and thickness of the medial gastrocnemius (MG) were analyzed at rest (i.e., θp, Flp, and tp, respectively), at 50% of maximal voluntary contraction (MVC) (i.e., θ50, Fl50, and t50, respectively), and during MVC (i.e., θ100, Fl100, and t100, respectively). Tendon elongation (TE) was measured by tracking the proximal displacement of the myotendinous junction of the MG during ramp isometric contraction. During ramp isometric contraction, the slope of the load–deformation relationship of the gastrocnemius tendon above 50% MVC was defined as an index of stiffness. After training, muscle thickness and fascicle angle increased significantly at rest and during contraction, whereas fascicle length increased at rest and did not change during contraction. Furthermore, the stiffness of the gastrocnemius tendon increased significantly. The results suggest that the behavior of muscle architecture and tendon mechanical properties are affected differently by strength training. Muscle Nerve, 2009

Spinal reflex plasticity during maximal dynamic contractions after eccentric training.

PURPOSE The aim of the study was to use eccentric strength training of the plantar flexor muscles to investigate the plasticity of the spinal reflexes during maximal voluntary isometric, concentric, and eccentric contractions. METHODS Eighteen healthy male subjects were divided into an eccentric strength training group (N = 10) and a control group (N = 8). The training program consisted of 18 sessions of eccentric exercise for a 7-wk period. All subjects were tested before, during, and after the training program. Soleus (SOL) and medial gastrocnemius (MG) spinal reflexes (H-reflex and V-wave) and M-waves were evoked at the same angular position during passive isometric, concentric, and eccentric actions (i.e., Hmax and Mmax, respectively) and during maximal voluntary isometric, concentric, and eccentric plantar flexion (MVC) (i.e., Hsup, V-wave, and Msup, respectively). RESULTS : Both SOL and MG Hmax/Mmax ratios remained unchanged whatever the action type after training. The Hsup/Msup ratio was increased only during eccentric MVC for the SOL (P < 0.01) and regardless of the contraction type for the MG (P < 0.05). The eccentric SOL Hsup/Msup ratio was not different from the isometric and concentric Hsup/Msup ratios after 7 wk of training. The V/Msup ratios were increased during isometric and eccentric contractions for the SOL and regardless of the contraction type for the MG after training. CONCLUSION : In conclusion, the present results suggest that the increase in voluntary torque induced by eccentric training could be ascribed, according to the contraction type, to an increased volitional drive from the supraspinal centers, which may induce neural adaptations at the spinal level. Changes in the regulation of the balance between excitation and inhibition affecting the motoneuron pool were suggested to explain the plasticity of the spinal reflexes.

Specific modulation of corticospinal and spinal excitabilities during maximal voluntary isometric, shortening and lengthening contractions in synergist muscles

Non‐technical summary  The neural control of muscle activity differs during voluntary shortening and lengthening contractions. In this paper, we show that the relative contribution of both cortical and spinal mechanisms to the modulation of neural activation is specific during lengthening contraction and differs between synergist muscles. Knowledge of spinal and corticospinal excitabilities modulations during shortening and lengthening muscle contraction improves our understanding of the processes that underlies the neural control of muscles during dynamic contractions.

Does eccentric endurance training improve walking capacity in patients with coronary artery disease? A randomized controlled pilot study:

Objective: To examine the effect of eccentric endurance training on exercise capacities in patients with coronary artery disease. Design: Randomized parallel group controlled study. Setting: Cardiac rehabilitation unit, Dijon University Hospital. Participants: Fourteen patients with stable coronary artery disease after percutaneous coronary intervention. Intervention: Patients followed 15 sessions of training (1 session per day, 3 days a week), either in the concentric group, following a standard programme, or in the eccentric group, performing eccentric resistance exercises using both lower limbs on a specifically designed ergometer. Main outcomes measured: Symptom-limited Vo2, peak workload, isometric strength of leg extensor and ankle plantar flexors, distance covered during the 6-minute walk test and time to perform the 200-m fast walk test in both groups, before and after the training period. Results: Patients did not report any adverse effects and were highly compliant. All measured parameters improved in eccentric and concentric group, except for 200-m fast walk test: symptom-limited Vo2 (+14.2% versus +4.6%), peak workload (+30.8% versus +19.3%), 6-minute walk test distance walked (+12.6% versus +10.1%) and leg extensor strength (+7% versus +13%) improved to a similar degree in both groups (P<0.01); ankle plantar flexor strength improved in both groups with a significantly greater increase in the eccentric group (+17% versus +7%, P<0.05). Conclusion: Patients with stable coronary artery disease can safely engage in eccentric endurance training, which appears to be as efficient as usual concentric training, with reduced oxygen consumption.

Effect of gender and obesity on electrical current thresholds

Introduction: In this study we investigated the influence of gender and obesity on electrical current thresholds in an attempt to optimize the application of skeletal muscle electrical stimulation (ES) in clinical practice. Methods: Thirty‐two obese and 35 age‐matched, non‐obese men and women received graded ES to the quadriceps muscle for sensory (detection) and motor (contraction) threshold assessment. Concomitant pain and tolerance to ES were recorded. Results: Sensory threshold was lower in women than in men (P < 0.001), both obese and non‐obese. Sensory and motor thresholds were higher in obese than in non‐obese subjects (P < 0.05), and body mass index was a strong predictor of motor excitability (r2 = 0.56–0.61). Current tolerance to motor stimulation was reduced in obese individuals, particularly in women, whereas pain was not influenced by gender or obesity. Conclusions: We suggest that both gender and obesity factors should be carefully considered in the design of rational ES treatments. Muscle Nerve, 2011

Effect of angular velocity on soleus and medial gastrocnemius H-reflex during maximal concentric and eccentric muscle contraction

At rest, the H-reflex is lower during lengthening than shortening actions. During passive lengthening, both soleus (SOL) and medial gastrocnemius (MG) H-reflex amplitudes decrease with increasing angular velocity. This study was designed to investigate whether H-reflex amplitude is affected by angular velocity during concentric and eccentric maximal voluntary contraction (MVC). Experiments were performed on nine healthy men. At a constant angular velocity of 60 degrees /s and 20 degrees /s, maximal H-reflex and M-wave potentials were evoked at rest (i.e., H(max) and M(max), respectively) and during concentric and eccentric MVC (i.e., H(sup) and M(sup), respectively). Regardless of the muscle, H(max)/M(max) was lower during lengthening than shortening actions and the H(sup)/M(sup) ratio was higher than H(max)/M(max) during lengthening actions. Whereas no action type and angular velocity effects on the MG H(sup)/M(sup) were found, the SOL H(sup)/M(sup) was lower during eccentric than concentric MVC and this depression was increased with higher angular velocity. Our findings indicate that the depression of the H-reflex amplitude during eccentric compared to concentric MVC depends mainly on the amount of inhibition induced by lengthening action. In conclusion, H-reflex should be evoked during both passive and active dynamic trials to evaluate the plasticity of the spinal loop.

Specific modulation of spinal and cortical excitabilities during lengthening and shortening submaximal and maximal contractions in plantar flexor muscles

This study investigated the influence of the torque produced by plantar flexor muscles on cortical and spinal excitability during lengthening and shortening voluntary contractions. To that purpose, modulations of motor-evoked potential (MEP) and Hoffmann (H) reflex were compared in the soleus (SOL) and medial gastrocnemius (MG) during anisometric submaximal and maximal voluntary contraction (MVC) of the plantar flexor muscles. For the submaximal shortening and lengthening contractions, the target torque was set at 50% of their respective MVC force. The results indicate that the amplitudes of both MEP and H-reflex responses, normalized to the maximal M wave, were significantly (P < 0.05) lower during lengthening compared with shortening submaximal contraction. For these two parameters, the reduction reached, respectively, 22.1 and 31.9% for the SOL and 34.5 and 29.3% for the MG. During MVC, normalized MEP and H reflex of the SOL were both reduced significantly by 19.9% (P < 0.05) and 29.9% (P < 0.001) during lengthening and shortening contraction, respectively, whereas no significant change (P > 0.05) was observed for MG. In addition, the silent period in the ongoing electromyogram (EMG) activity following the MEP was significantly (P < 0.01) briefer during lengthening than shortening contractions but did not differ (P > 0.05) between contraction intensities and muscles. Together, these results indicate that cortical and spinal mechanisms involved in the modulation of muscle activation during shortening and lengthening contractions differ between synergistic muscles according to the torque produced. Data further document previous studies reporting that the specific modulation of muscle activation during lengthening contraction is not torque dependent.

The 200-m fast-walk test compared with the 6-min walk test and the maximal cardiopulmonary test: a pilot study.

Gremeaux V, Deley G, Duclay J, Antoine D, Hannequin A, Casillas JM: The 200-m fast-walk test compared with the 6-min walk test and the maximal cardiopulmonary test: A pilot study. Objective:The 200-m fast-walk test has been proposed as a high- intensity performance test in healthy, elderly subjects. Adaptation of low-risk coronary artery disease patients during this test were compared with those in a 6-min walk test and a maximal cardiopulmonary exercise test. Design:Thirty patients with stable coronary artery disease (51.9 ± 8.7 yrs), referred to the cardiac rehabilitation department, performed a cardiopulmonary exercise test, then a 200-m fast-walk test and a 6-min walk test in a random order, before and after the training period (6 wks, 3 days per week). Heart rate was monitored during each test. Peak workload of cardiopulmonary exercise test, distance walked on the 6-min walk test, and time to perform the 200-m fast-walk test were measured. A subsample of ten patients performed the exercise test with gas exchange measurements, with ventilatory threshold determination. Results:All subjects completed walk tests without complaint or incidents. Compared with the cardiopulmonary exercise test, the cardiac relative intensity was higher during the 200-m fast-walk test than during the 6-min walk test, both before (89.6% vs. 78.1% of cardiopulmonary exercise test maximal heart rate; P < 0.05) and after (83.8% vs. 74.3%; P < 0.05) training. Among the subsample of ten patients, the 200-m fast-walk test heart rate was significantly higher than the ventilatory threshold heart rate, which did not differ from the 6-min walk test heart rate. The 200-m fast-walk test time significantly decreased after training (−9.1%, P < 0.01). Conclusion:In patients with coronary artery disease at low risk, the 200-m fast-walk test explores higher levels of cardiorespiratory capacity than the 6-min walk test. Thus, this could be a useful field test in complement to the cardiopulmonary exercise test to assess functional capacity improvement and update training targets regularly during the course of high-intensity rehabilitation programs in this population.

Neural drive preservation after detraining following neuromuscular electrical stimulation training

The purpose of the study was to investigate the behaviour of the central nervous system when 5 weeks of neuromuscular electrical stimulation (NMES) training was followed by 5 weeks of detraining. Nineteen males were divided into the neuromuscular electrostimulated group (EG, n=12) and the control group (CG, n=7). The training program consisted of 15 sessions of isometric NMES over a 5-week period. The EG subjects were tested before training (PRE), after 5 weeks of NMES training (POST) and after 5 weeks of detraining (DE) while CG subjects were only tested at PRE and at POST. Soleus (SOL) and gastrocnemii (GAS) maximal H-reflex and M-wave potentials were evoked at rest (i.e., H(max) and M(max), respectively) and during maximal voluntary contraction (MVC) (i.e., H(sup) and M(sup), respectively). SOL and GAS V-wave were recorded by supramaximal stimulation delivered during MVC. SOL and GAS electromyographic (EMG) activity as well as muscle activation were also assessed during MVC. After training, plantar flexor MVC increased significantly by 22% (P<0.001). Torque gains were associated with an increase in muscle activation (P<0.05), SOL and GAS normalized EMG activity (P<0.01 and P<0.05, respectively) and V/M(sup) ratios (P<0.01 and P<0.05, respectively). No significant changes occurred in any of these parameters between POST and DE. H(max)/M(max) and H(sup)/M(sup) ratios for both muscles were unchanged after both the training and detraining periods. In conclusion, the NMES training-induced neural adaptations were maintained after detraining, suggesting that neural changes are long-lasting and did not affect the elements of H-reflex pathways.

Unchanged H-reflex during a sustained isometric submaximal plantar flexion performed with an EMG biofeedback

The aim of this study was to assess H-reflex plasticity and activation pattern of the plantar flexors during a sustained contraction where voluntary EMG activity was controlled via an EMG biofeedback. Twelve healthy males (28.0+/-4.8 yr) performed a sustained isometric plantar flexion while instructed to maintain summed EMG root mean square (RMS) of gastrocnemius lateralis (GL) and gastrocnemius medialis (GM) muscles fixed at a target corresponding to 80% maximal voluntary contraction torque via an EMG biofeedback. Transcutaneous electrical stimulation of the posterior tibial nerve was evoked during the contraction to obtain the maximal H-reflex amplitude to maximal M-wave amplitude ratio (H(sup)/M(sup) ratio) from GL, GM and soleus (SOL) muscles. Neuromuscular function was also assessed before and immediately after exercise. Results showed a decrease in SOL activation during sustained flexion (from 65.5+/-6.4% to 42.3+/-3.8% maximal EMG, p<0.001), whereas summed EMG RMS of GL and GM remained constant (59.7+/-4.8% of maximal EMG on average). No significant change in the H(sup)/M(sup) ratio was found for SOL, GL and GM muscles. Furthermore, it appears that the decrease in maximal voluntary contraction torque (-20.4+/-2.9%, p<0.001) was related to both neural and contractile impairment. Overall, these findings indicate that the balance between excitation and inhibition affecting the motoneuron pool remains constant during a sustained contraction where myoelectrical activity is controlled via an EMG biofeedback or let free to vary.