1,721,005 research outputs found
Last word on viewpoint: Even more recipes to try, yet know what to put in the pan, as well as when and why
No full textElectrical and mechanical Hmax-to-Mmax ratio in power- and endurance-trained athletes
No full textThe 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-tomaximal M-wave ratios for both force output (twitch) and EMG wave amplitude were significantly lower in powertrained than endurance-trained athletes. However, powertrained 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 a-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
Differences in climbing-specific strength between boulder and lead rock climbers.
Full text linkDifferences in climbing-specific strength between boulder and lead rock climbers. J Strength Cond Res 27(2): 310-314, 2013-The purpose of this study was to compare maximal muscle strength and rapid force capacity of finger flexors between boulder and lead climbers of national-international level. Ten boulder (mean ± SD, age 27 ± 8 years) and 10 lead climbers (age 27 ± 6 years) volunteered for the study. Ten nonclimbers (age 25 ± 4 years) were also tested. Isometric maximal voluntary contraction (MVC) force and rate of force development (RFD) produced in "crimp" and "open-crimp" hand positions were evaluated on an instrumented hold. Climbers were stronger than nonclimbers. More interestingly, MVC force and RFD were significantly greater in boulder compared with lead climbers (p < 0.05), in both crimp and open-crimp positions. The RFD was the most discriminatory outcome, as the largest difference between boulder and lead climbers (34-38%) was observed for this variable. The RFD may reflect the specific requirements of bouldering and seems to be more appropriate than pure maximal strength for investigating muscle function in rock climbers
The relative contribution to the plantar flexor torque of the soleus motor units activated by the H reflex and M response in humans.
No full textThis study proposes a method of quantifying the relative contribution to the plantar- ̄exor 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 Hrecruitment 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 Mwas estimated, for the range of Mwaves including those accompanying Hmax. 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 ®nding is discussed. A simple formula for assessing the contribution of the H wave to the twitch torque is given
A vertical jump force test for assessing bilateral strength asymmetry in athletes
No full textPURPOSE: To establish the validity and reliability of a new vertical jump force test (VJFT) for the assessment of bilateral strength asymmetry in a total of 451 athletes. METHODS: The VJFT consists of countermovement jumps with both legs simultaneously: one on a single force platform, the other on a leveled wooden platform. Jumps with the right or the left leg on the force platform were alternated. Bilateral strength asymmetry was calculated as [(stronger leg - weaker leg)/stronger leg] × 100. A positive sign indicates a stronger right leg; a negative sign indicates a stronger left leg. Studies 1 (N = 59) and 2 (N = 41) examined the correlation between the VJFT and other tests of lower-limb bilateral strength asymmetry in male athletes. In study 3, VJFT reliability was assessed in 60 male athletes. In study 4, the effect of rehabilitation on bilateral strength asymmetry was examined in seven male and female athletes 8-12 wk after unilateral knee surgery. In study 5, normative data were determined in 313 male soccer players. RESULTS: Significant correlations were found between VJFT and both the isokinetic leg extension test (r = 0.48; 95% confidence interval, 0.26-0.66) and the isometric leg press test (r = 0.83; 0.70-0.91). VJFT test-retest intraclass correlation coefficient was 0.91 (0.85-0.94), and typical error was 2.4%. The change in mean [-0.40% (-1.25 to 0.46%)] was not substantial. Rehabilitation decreased bilateral strength asymmetry (mean ± SD) of the athletes recovering from unilateral knee surgery from 23 ± 3 to 10 ± 4% (P < 0.01). The range of normal bilateral strength asymmetry (2.5th to 97.5th percentiles) was -15 to 15%. CONCLUSIONS: The assessment of bilateral strength asymmetry with the VJFT is valid and reliable, and it may be useful in sports medicine. ©2007The American College of Sports Medicine
Architectural changes in superficial and deep compartments of the tibialis anterior during electrical stimulation over different sites
Full text linkElectrical stimulation is widely used in rehabilitation to prevent muscle weakness and to assist the functional recovery of neural deficits. Its application is however limited by the rapid development of muscle fatigue due to the non-physiological motor unit (MU) recruitment. This issue can be mitigated by interleaving muscle belly (mStim) and nerve stimulation (nStim) to distribute the temporal recruitment among different MU groups. To be effective, this approach requires the two stimulation modalities to activate minimally-overlapped groups of MUs. In this manuscript, we investigated spatial differences between mStim and nStim MU recruitment through the study of architectural changes of superficial and deep compartments of tibialis anterior (TA). We used ultrasound imaging to measure variations in muscle thickness, pennation angle, and fiber length during mStim, nStim, and voluntary (Vol) contractions at 15% and 25% of the maximal force. For both contraction levels, architectural changes induced by nStim in the deep and superficial compartments were similar to those observed during Vol. Instead, during mStim superficial fascicles underwent a greater change compared to those observed during nStim and Vol, both in absolute magnitude and in their relative differences between compartments. These observations suggest that nStim results in a distributed MU recruitment over the entire muscle volume, similarly to Vol, whereas mStim preferentially activates the superficial muscle layer. The diversity between spatial recruitment of nStim and mStim suggests the involvement of different MU populations, which justifies strategies based on interleaved nerve/muscle stimulation to reduce muscle fatigue during electrically-induced contractions of TA
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