Biomedical subjects

N A Maffiuletti

Publications and source records attributed to N A Maffiuletti.

24 records · Page 2Linked to original sources

PubMed2001

Progressive versus rapid rate of contraction during 7 wk of isometric resistance training.

PURPOSE: The aim of this study was to compare the effects of isometric training performed with progressive versus rapid rate of contraction on the knee extensor neuromuscular properties over a 7-wk period. METHODS: Sixteen healthy male subjects trained quadriceps femoris muscle in a leg extension machine three times a week during 7 wk. The training sessions consisted of six sets of six maximal isometric contractions. A first group trained by performing progressive contractions lasting 4 s, whereas a second group performed contractions with a rapid rate of contraction (i.e., ballistic contractions) lasting about 1 s. RESULTS: Both groups significantly increased the isometric and isokinetic voluntary torque, and the respective absolute or relative gains were comparable. Isometric training performed with progressive rate of contraction affected the evoked action potential (M wave) of the vastus lateralis muscle and not the related twitch properties. On the other hand, the isometric training completed with ballistic contractions significantly modified the twitch contractile properties of the knee extensors and not the associated M waves of both vastus medialis and vastus lateralis. CONCLUSION: Knee extensors adapted specifically their neuromuscular properties to the type of rate of contraction performed during 7-wk isometric resistance training. Progressive isometric contractions produced modifications of the nervous system at peripheral level (i.e., muscle membrane electrical activity), whereas ballistic isometric contractions affected the knee extensor contractile muscle properties (i.e., excitation-contraction coupling).

Adult↗

PubMed2001

Effect of cycling cadence on contractile and neural properties of knee extensors.

PURPOSE: This study investigated the effect of prior prolonged cycling exercise performed at different cadences on subsequent neuromuscular characteristics. METHODS: Eight well-trained triathletes sustained 80% of their maximal aerobic power during 30 min at three cadences: the freely chosen cadence (FCC), FCC-20%, and FCC+20%. Maximal isometric and concentric (120 degrees x s(-1) and 240 degrees x s(-1)) torques were recorded before and after the exercise. Central activation, neural (M-wave), and contractile (isometric muscular twitch) parameters of quadriceps muscle were also analyzed by electrical stimulation of the femoral nerve. RESULTS: Reductions in maximal isometric (P < 0.01) and concentric torques at 120 degrees x s(-1) (P < 0.05) were found after exercise. Central activation levels fell significantly (P < 0.05) by 13-16% depending on the pedaling rate. Although the M-wave did not significantly change after exercise, the ratio EMG RMS/M-wave amplitude decreased significantly (P < 0.01) on both vastus lateralis and vastus medialis muscles for FCC-20% and FCC but not for FCC+20%. Significant decreases in maximal twitch tension (P < 0.01), maximal rate of twitch development (P < 0.01), and time to half relaxation (P < 0.01) were observed postexercise with no effect of cadence. CONCLUSIONS: These findings suggest that force reduction after prolonged cycling is attributable to both central and peripheral factors but is not influenced by the pedaling rate in a range of FCC +/- 20%.

Adult↗

PubMed2001

Electrical and mechanical H(max)-to-M(max) ratio in power- and endurance-trained athletes.

The aim of this study was to compare the mechanical and electromyographic (EMG) characteristics of soleus motor units activated during maximal H reflex and direct M response among subjects with different histories of physical activity. Power-trained athletes produced stronger twitches, with a higher rate of twitch tension buildup and relaxation, than their endurance counterparts for both maximal H-reflex and maximal M-wave responses. The maximal H-reflex-to-maximal M-wave ratios for both force output (twitch) and EMG wave amplitude were significantly lower in power-trained than endurance-trained athletes. However, power-trained athletes exhibited a significantly greater twitch-to-EMG ratio for the reflexly activated motor units with respect to the entire motor pool, whereas endurance-trained athletes had comparable twitch-to-EMG ratios for both reflexly and directly activated units. Power training increases the force output of the whole ensemble of the motor units, thereby compensating for the lower efficacy of the reflex transmission between Ia spindle afferent input and soleus alpha-motoneuron. On the other hand, the lower level of force evoked by the reflexly activated units in endurance-trained athletes is associated with a greater motor pool reflex excitability. Therefore, endurance-trained athletes produce the necessary force by recruitment of more slow-twitch units than do other subjects for comparable levels of force and type of task.

Adult↗

PubMed2000

The relative contribution to the plantar-flexor torque of the soleus motor units activated by the H reflex and M response in humans.

This study proposes a method of quantifying the relative contribution to the plantar-flexor torque of soleus H and M responses evoked by tibial nerve stimulation. For ten subjects, the amplitude of the twitch produced by the H wave was plotted against the corresponding potential, for stimuli producing H without M (i.e. in the ascending portion of the H-recruitment curve). It was then assumed that the contribution of H to twitches produced by M plus H was similar for similar H waves on the curve-descending portion. Hence, the contribution of M was estimated, for the range of M waves including those accompanying H(max). The estimated mechanical contributions of H and M wave increase linearly with their potentials, the slope of the relationship being greater for H than M. The interpretation of this finding is discussed. A simple formula for assessing the contribution of the H wave to the twitch torque is given.

Action Potentials↗

PubMed2000

The effects of a prolonged running exercise on strength characteristics.

The aim of this study was to examine concentric, isometric, and eccentric strength reductions in the quadriceps muscle following a prolonged running exercise. Before and after a 2 h run (28.4+/-1.4 km) peak torque (PT) of the knee extensors at angular velocities of -120, -90, -60, 0, 60, 120, 180, 240 degrees x s(-1) using an isokinetic dynamometer, electromyographic (EMG) activity of the vastus lateralis (VL) and vastus medialis (VM) muscles and height of a counter movement jump were recorded in twelve well-trained triathletes. Counter movement jump performances decreased by 10% and PT values were all significantly lower (p < 0.01) at each angular velocity following the run. The torque loss was significantly (p < 0.01) greater under eccentric contractions (from 18 to 21%) than under concentric ones (from 11 to 14%). EMG activity (RMS) was lower in both VL and VM muscles after the 2 h run but no difference existed in RMS losses between concentric and eccentric contractions. The present results demonstrate that 1) a prolonged running exercise more greatly affects eccentric force production in the quadriceps muscle, and 2) this specificity seems to be due to an impairment of the muscular contractile mechanism rather than a modification to the neural input.

Adult↗

PubMed2000

The effects of electromyostimulation training and basketball practice on muscle strength and jumping ability.

The aim of this study was to investigate the influence of a 4-week electromyostimulation training program on the strength of the knee extensors and the vertical jump performance of 10 basketball players. Electromyostimulation sessions were carried out 3 times weekly; each session consisted of 48 contractions. Testing was carried out before and after the electromyostimulation training program (week 4) and once more after 4 weeks of normal basketball training (week 8). At week 4, isokinetic strength increased significantly (p < 0.05) at eccentric and high concentric velocities (between 180 and 360 x s(-1)); this was not the case for low concentric velocities (60 and 120 degrees x s(-1)). Electromyostimulation training increased also isometric strength at the two angles adjacent to the training angle (p < 0.01). Squat jump increased significantly by 14% at week 4 (p < 0.01), whereas counter movement-jump showed no change. At week 8, gains in isokinetic, isometric strength and squat-jump performance were maintained and the counter movement jump performance increased significantly by 17% (p<0.01). Electromyostimulation as part of a short strength-training program enhanced knee extensor strength and squat jump performance of basketball players.

Adult↗