Biomedical subjects

Alain Martin

Publications and source records attributed to Alain Martin.

24 records · Page 2Linked to original sources

PubMed2005

Muscular performances at the ankle joint in young and elderly men.

The effect of aging on mechanical and electromyographic characteristics of ankle joint muscles was investigated in 11 young (mean age 24 years) and 12 elderly (mean age 77 years) males. Maximal and submaximal isometric voluntary torques were measured during ankle plantarflexion and dorsiflexion. Electromyographic activities of triceps surae and tibialis anterior muscles were recorded. The elderly group developed equal maximal dorsiflexion torques (42 vs 45 N.m, p >.05), but in plantarflexion, the elderly group was weaker (80 vs 132 N.m, p <.001) and presented a decreased twitch amplitude (11 vs 16 N.m) and lower coactivation (8% vs 15%) than that of the young adults. We established a linear relationship between the percentage of coactivation and developed resultant torque. Our results showed that dorsiflexor muscles were not affected by aging, contrary to plantarflexors, in which the decline in torque was partly explained by changes intervening at the peripheral level.

Adult↗

PubMed2005

Electromyostimulation training effects on neural drive and muscle architecture.

PURPOSE: The purpose of the study was to investigate the effect of 4 and 8 wk of electromyostimulation (EMS) training on both muscular and neural adaptations of the knee extensor muscles. METHODS: Twenty males were divided into the electrostimulated group (EG, N = 12) and the control group (CG, N = 8). The training program consisted of 32 sessions of isometric EMS over an 8-wk period. All subjects were tested at baseline (B) and retested after 4 (WK4) and 8 (WK8) wk of EMS training. The EMG activity and muscle activation obtained under maximal voluntary contractions (MVC) was used to assess neural adaptations. Torque and EMG responses obtained under electrically evoked contractions, muscle anatomical cross-sectional area (ACSA), and vastus lateralis (VL) pennation angle, both measured by ultrasonography imaging, were examined to analyze muscular changes. RESULTS: At WK8, knee extensor MVC significantly increased by 27% (P < 0.001) and was accompanied by an increase in muscle activation (+6%, P < 0.01), quadriceps muscle ACSA (+6%, P < 0.001), and VL pennation angle (+14%, P < 0.001). A significant increase in normalized EMG activity of both VL and vastus medialis (VM) muscles (+69 and +39%, respectively, P < 0.001) but not of rectus femoris (RF) muscle was also found at WK8. The ACSA of the VL, VM, and vastus intermedius muscles significantly increased at WK8 (5-8%, P < 0.001) but not at WK4, whereas no changes occurred in the RF muscle. CONCLUSION: We concluded that the voluntary torque gains obtained after EMS training could be attributed to both muscular and neural adaptations. Both changes selectively involved the monoarticular vastii muscles.

Electric Stimulation↗

PubMed2004

Muscle plasticity after weight and combined (weight + jump) training.

PURPOSE: The purpose of this study was to compare the effects of jump training as a complement to weight training on jump performance and muscle strategy during the squat and countermovement jump. METHOD: Twenty-two male handball players, between the ages of 17 and 24, and in good health, were randomly divided into three groups. Two were trained groups, weight training (WTG) and jump training combined with weight training (CTG), and one was a control group (CG). Maximal isometric force and maximal concentric power were assessed by a supine leg press, squat jump (SJ), counter movement jump (CMJ), and surface EMG was used to determine changes in muscle adaptation before and after the training period. RESULTS: After 6-wk training programs, the two training groups increased maximal isometric force, maximal concentric power, and squat jump performance. However, only combined training presented a significant increase in height jump performance during the countermovement jump (P < 0.05). EMG analysis (as interpreted through the root mean square values) showed that the SJ was performed similarly before and after the training period for the two training groups. However, during the CMJ, only the CTG group adopted a new technique manifested by a short transition phase together with an increase in knee joint stiffness and knee extensor muscle activation and rectus femoris ratio. CONCLUSION: It was suggested that the central activities in knee joint during the transition phase, in conjunction with intrinsic muscle contractile properties, play a major role in the regulation of performance during a CMJ. Furthermore, our study suggests that a change in maximal strength and/or explosive strength does not necessarily cause changes in combined movement such as the stretch shortening cycle.

Electromyography↗

PubMed2003

Effect of electromyostimulation training on soleus and gastrocnemii H- and T-reflex properties.

When muscle is artificially activated, as with electromyostimulation (EMS), action potentials are evoked in both intramuscular nerve branches and cutaneous receptors, therefore activating spinal motoneurons reflexively. Maximal soleus and gastrocnemii H- and T-reflex and the respective mechanical output were thus quantified to examine possible neural adaptations induced at the spinal level by EMS resistance training. Eight subjects completed 16 sessions of isometric EMS (75 Hz) over a 4-week period. Maximal soleus and gastrocnemii M wave (M(max)), H reflex (H(max)) and T reflex (T(max)) were compared between before and after training, together with the corresponding plantar flexor peak twitch torque. No significant changes were observed for electromechanical properties of H(max) reflex following EMS. On the other hand, peak twitch torque produced by T(max), but not by equal-amplitude H reflex, significantly increased as a result of training (+21%, P<0.05). These changes were associated with a trend towards a significant increase for normalized gastrocnemii (+21%, P=0.07) but not soleus T(max) reflex. It is concluded that, contrary to results previously obtained after voluntary physical training, EMS training of the plantar flexor muscles did not affect alpha motoneuron excitability and/or presynaptic inhibition, as indicated by H-reflex results. On the other hand, in the absence of change in a control group, T(max) electromechanical findings indicated that: (1). equal-amplitude H- and T-reflex adapted differently to EMS resistance training; and (2). EMS had an effect on gastrocnemii but not on soleus muscle, perhaps because of the differences in respective motor unit characteristics (e.g., axon diameter).

Action Potentials↗

PubMed2003

Neuromuscular fatigue after a ski skating marathon.

The aim of this study was to characterize neuromuscular fatigue in knee extensor muscles after a marathon skiing race (mean +/- SD duration = 159.7 +/- 17.9 min). During the 2 days preceding the event and immediately after, maximal percutaneous electrical stimulations (single twitch, 0.5-s tetanus at 20 and 80 Hz) were applied to the femoral nerve of 11 trained skiers. Superimposed twitches were also delivered during maximal voluntary contraction (MVC) to determine maximal voluntary activation (% VA). EMG was recorded from the vastus lateralis muscle. MVC decreased with fatigue from 171.7 +/- 33.7 to 157.3 +/- 35.2 Nm (-8.4%; p < 0.005) while % VA did not change significantly. The RMS measured during MVC and peak-to-peak amplitude of the compound muscle action potential (PPA) from the vastus lateralis decreased with fatigue by about 30% (p < 0.01), but RMS.PPA-1 was similar before and after the ski marathon. Peak tetanus tension at 20 Hz and 80 Hz (P(0)20 and P(0)80, respectively) did not change significantly, but P(0)20.P(0)80-1 increased (p < 0.05) after the ski marathon. Data from electrically evoked single twitches showed greater peak mechanical response, faster rate of force development, and shorter contraction time in the fatigued state. From these results it can be concluded that a ski skating marathon (a) alters slightly but significantly maximal voluntary strength of the knee extensors without affecting central activation, and (b) induces both potentiation and fatigue.

Adult↗

PubMed2002

Activation of human plantar flexor muscles increases after electromyostimulation training.

Neuromuscular adaptations of the plantar flexor muscles were assessed before and subsequent to short-term electromyostimulation (EMS) training. Eight subjects underwent 16 sessions of isometric EMS training over 4 wk. Surface electromyographic (EMG) activity and torque obtained under maximal voluntary and electrically evoked contractions were analyzed to distinguish neural adaptations from contractile changes. After training, plantar flexor voluntary torque significantly increased under isometric conditions at the training angle (+8.1%, P < 0.05) and at the two eccentric velocities considered (+10.8 and +13.1%, P < 0.05). Torque gains were accompanied by higher normalized soleus EMG activity and, in the case of eccentric contractions, also by higher gastrocnemii EMG (P < 0.05). There was an 11.9% significant increase in both plantar flexor maximal voluntary activation (P < 0.01) and postactivation potentiation (P < 0.05), whereas contractile properties did not change after training. In the absence of a change in the control group, it was concluded that an increase in neural activation likely mediates the voluntary torque gains observed after short-term EMS training.

Adult↗