121,855 research outputs found
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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
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
Differences in climbing-specific strength between boulder and lead rock climbers.
No full textDifferences 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
Combined evaluation of resting IGF-I, N-terminal propeptide of type III procollagen (PIIINP) and C-terminal cross-linked telopeptide of type I collagen (ICTP) levels might be useful for detecting inappropriate GH administration in athletes: a preliminary
No full textOBJECTIVE
To verify whether combined measurements
of GH-dependent parameters might be useful in detecting
exogenous recombinant GH (rGH) administration
in male athletes from different disciplines.
METHODS
Sixty-six athletes (control group) were
sampled for the evaluation of resting IGF-I, N-terminal
propeptide of type III procollagen (PIIINP) and telopeptide
type I collagen (ICTP). Cut-off values (mean +
2 SD)
for IGF-I, PIIINP and ICTP were calculated and arbitrary
scores (1·5, 2·0) were assigned to abnormal parameters.
By using the sum of individual parameter scores,
positive (≥
3) or negative (< 3) scores were obtained.
In addition, a subgroup of six athletes was treated
for 3 weeks with rGH (0·09 IU/kg body weight, 6 days/
week) and was similarly evaluated at the end of the 1st,
2nd and 3rd week (i.e. 18 samples)
Reproducibility and validity of the Italian version of the International Physical Activity Questionnaire in obese and diabetic patients
No full textPurpose: Aims of this study were to evaluate the agreement between the short and long versions of the International Physical Activity Questionnaire (IPAQ: Italian versions), their reproducibility (agreement and reliability) and construct validity (relative to pedometry) in a clinical population. Methods: Ninety patients affected by obesity (N = 39), type 2 diabetes mellitus (N = 26) or both (N = 25) were recruited. They were asked to maintain their usual physical activity habits during two consecutive weeks and to fill the questionnaires twice (at the end of each week). They were also asked to wear a pedometer for 7 consecutive days after the first administration of the questionnaires. Results: We found acceptable agreement between the IPAQ short and long versions (ICC2,1 values were 0.81 and 0.77 for the 1st and 2nd administration), uncertain reproducibility (acceptable reliability but poor agreement) and inadequate validity relative to pedometry (the correlation coefficients between all IPAQ scores and daily steps were <0.50) for both IPAQ short and IPAQ long. Conclusions: The IPAQ use may be justified in daily clinical practice and in clinical research (e.g., in cross-sectional studies) for a simple and rapid evaluation of the physical activity level for discriminative purposes. However, the use of these questionnaires does not appear suitable for prospective interventional studies in which the level of physical activity of the recruited patients has to be assessed over time
GH responses to two consecutive bouts of whole body vibration, maximal voluntary contractions or vibration alternated with maximal voluntary contractions administered at 2-h intervals in healthy adults
No full textBackground: Pharmacological or exercise stimuli repeated at a short interval (but not electrical muscle stimulation) are associated with a blunting of GH responsiveness. Aim: To compare GH responses to repeated bout of three different GH-releasing stimuli. Methods: The effects of two consecutive bouts (with a 2-h interval) of whole body vibrations (WBV), maximal voluntary contractions alone (MVC), or alternated with WBV (MVC-WBV) on blood GH and lactate (LA) were assessed in nine young males. Results: Baseline levels of both GH and LA increased significantly after the first bout of all the tested stimuli, and were significantly lower after WBV than after MVC or MVC alternated with WBV, no difference being detected between these last. The administration of a second bout resulted in significantly lower GH increases than those elicited in the first bout in the three different tests; significantly lower LA responses were recorded after the second bout of MVC and MVC-WBV when compared with those obtained after the first bout, while no significant differences were observed after the two WBV bouts for LA. All responses after the second bout of MVC and MVC-WBV were significantly higher than those observed after WBV alone. GH concentrations were significantly correlated with LA after all stimuli, although LA concentrations after the second bout were associated with markedly lower GH levels. Conclusions: A significant blunting of GH responsiveness ensues after a second bout of different GH-releasing stimuli, independent from the amount of GH released after the first bout. This is a pattern also observed for other pharmacological stimuli and exercise modalities, and suggests a common mechanism underlying different GH-releasing stimuli. © 2010 Growth Hormone Research Society
Effect of ageing on the electrical and mechanical properties of human soleus motor units activated by the H reflex and M wave
No full textThis study was designed to investigate the effect of ageing on the mechanical and electromyographic (EMG) characteristics of the soleus motor units (MUs) activated by the maximal Hoffmann reflex (Hmax) and by the direct muscle compound action potential (Mmax). Eleven young (mean age 25 ± 4 years) and ten elderly (mean age 73 ± 5 years) males took part in this investigation. The senior group presented lower amplitudes of Mmax (-57 %, P < 0.001) and Hmax (-68 %, P < 0.001) waves compared to the younger population. These were associated with a depression of relative twitch torque of the plantar flexors. The average values of the Hmax/Mmax ratio did not statistically differ between the two populations, despite a tendency for lower values (∼23 %) in the senior group. However, the older adults showed a greater relative amplitude of the sub-maximal M wave evoked at Hmax (MatHmax) than did the younger males (young 5 % vs. elderly 29 % of the Mmax, P < 0.01). This finding suggests an increased homogeneity between the excitability threshold of sensory and motor axons. The twitch torque at Hmax (PtH-M) was subsequently calculated by subtraction from the total twitch torque of the mechanical contamination associated with MatHmax. The resulting PtH-M was significantly lower in the elderly (-59 %, P < 0.001). Despite a discrepancy of 20 % between the two groups, the mechanical ratio (PtH-M/PtM; PtM, twitch tension related to the Mmax compound action potential), like the EMG ratio, did not statistically differ between the young and older individuals. Nevertheless, the senior subjects exhibited a higher twitch/EMG ratio for the reflexively activated MUs (PtH-M/Hmax) than the younger individuals (+40 %, P < 0.05). This finding suggests an on-going neuromuscular remodelling, resulting in an increased innervation ratio. The neural rearrangement may be viewed as a compensatory adaptation of the motor system to preserve the mechanical efficiency of the surviving MUs, despite the age-related impairment of the segmental reflex system. This phenomenon is confirmed by the maintenance, with senescence, of the approximately constant values of the twitch/EMG ratio for the entire motor pool (PtM/Mmax)
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