Force variability during isometric wrist flexion in highly skilled and sedentary individuals

The association of expertness in specific motor activities with a higher ability to sustain a constant application of force, regardless of muscle length, has been hypothesized. Ten highly skilled (HS group) young tennis and handball athletes and 10 sedentary (S group) individuals performed maximal and submaximal (5, 10, 20, 50, and 75% of the MVC) isometric wrist flexions on an isokinetic dynamometer (Kin-Com, Chattanooga). The wrist joint was fixed at five different angles (230, 210, 180, 150, and 1300). For each position the percentages of the maximal isometric force were calculated and participants were asked to maintain the respective force level for 5 s. Electromyographic (EMG) activation of the Flexor Carpi Ulnaris and Extensor Digitorum muscles was recorded using bipolar surface electrodes. No significant differences were observed in maximal isometric strength between HS and S groups. Participants of HS group showed significantly (P < 0.05) smaller force coefficient of variability (CV) and SD values at all submaximal levels of MVC at all wrist angles. The CV and SD values remained unaltered regardless of wrist angle. No difference in normalized agonist and antagonist EMG activity was observed between the two groups. It is concluded that long-term practice could be associated with decreased isometric force variability independently from muscular length and coactivation of the antagonist muscles

The influence of a strength training programme on the physical and kick performances of young soccer players

The aim of this study was to determine if physical and kick performances increase under a strength thing. For this purpose, 8 young french soccer players (age 15,75 & 0,71) took part in a 4 weeks strength training programme of the lower limbs. Squats, tricep and leg swings exercices were associated with pliometrics and a practice of specific soccer skills. In order to evaluate the relevance of this programme and some possible progress made by the players, a number of tests were set up.: - kick performances measured on a specific ball speed test showed significant improvements : 10,12 km/h (±4,31)(

Neuromuscular recovery after a strength training session in elderly people

Ageing is associated with an increased susceptibility to muscle damage but little is known on how this affects muscle recovery after exercise. Hence, this study is aiming at investigating the effects of a heavy-resistance training session of neuromuscular recovery of the calf muscles of a group of elderly men aged >65. Maximal isometric and isokinetic torque, muscle voluntary activation (VA) capacity, surface electromyographic activity (EMG), peak-to-peak amplitude of action potentials associated with twitch responses of plantar flexors were evaluated before and 5 min (post1), 24 h (post2) and 48 h (post3) after 10 sets of 10 repetitions of a calf raise exercise performed at an intensity of 70% of the individual, one repetition maximum. Blood samples were taken before and 1, 48, 96 and 144 h after the training session and assayed for serum creatine kinase (CK), lactate dehydrogenase (LDH) and myoglobin (Mb). Peak torque during eccentric and concentric (120\ub0 s-1) contractions and twitch parameters were significantly reduced at post1, and recovered completely at post2. No significant changes were found in integrated EMG, M-wave amplitudes and VA throughout the entire test period. CK and LDH concentrations reached peak values 48 h after the exercise session and returned to the pre-exercise values 96 h after the training session. Serum Mb level increased by 73.2% 1 h after exercise and recovered at 48 h. The reduction in peak torque following a strength training session in an elderly population could be explained mainly by fatigue of peripheral origin. After 24 h the elders recovered completely their capacities of strength production, despite muscle damage being still evident 48 h after the strength training session. \ua9 Springer-Verlag 2006

ASSESSMENT OF THE STRENGTH QUALITIES OF AN INTERNATIONAL RUGBY SQUAD

With a squad of 27 players of an international standard team, we were able to compare torque-velocity curves of the backs (N=13), third line forwards (6) and first and second line forwards (N=8). A Biodex type dynamometer ( Biodex corportation Shirley, NY,USA) was used. On the basis of this torque data we can propose an explosive power factor consisting in the ratio: peak torque over time taken to reach peak torque. This can be calculated for any speed. This factor was computed for the group of rugby players and results for the different positions compared. It can be seen that the factor increases for the backs. Their maximum factor occurs at the highest speed. For the other towo groups the profile is identical : the highest factor is at the lowest speed. It should be noted that this value is more than twice that found for the backs. We also calculated the difference between eccentric and concentric torque and its relation with the type of players. For Schmidt Bleicher (1985) the explosive power subjects who make the most of their absolute (eccentric) force are those who show the smallest difference. Our findings show the forwards are the most effective according to this parameter. We completed our study by measuring jumping ability using squatting jump, countermovement jump and 15s Bosco powe rtest. The results will be discussed. A “Rugby-press” was used for monitoring specific strength of rugby players

Test-retest reliability of dual-recorded brainstem versus cortical auditory-evoked potentials to speech

Background: Auditory-evoked potentials have proven useful in the objective evaluation of sound encoding at different stages of the auditory pathway (brainstem and cortex). Yet, their utility for use in clinical assessment and empirical research relies critically on the precision and test-retest repeatability of the measure. Purpose: To determine how subcortical/cortical classes of auditory neural responses directly compare in terms of their internal consistency and test-retest reliability within and between listeners. Research Design: A descriptive cohort study describing the dispersion of electrophysiological measures. Study Sample: Eight young, normal-hearing female listeners. Data Collection and Analysis: Werecorded auditory brainstemresponses (ABRs), brainstem frequencyfollowing responses (FFRs), and cortical (P1-N1-P2) auditory-evoked potentials elicited by speech sounds in the same set of listeners. We reassessed responses within each of four different test sessions over a period of 1 mo, allowing us to detect possible changes in latency/amplitude characteristics with finer detail than in previous studies. Results: Our findings show that brainstem and cortical amplitude/latency measures are remarkably stable; with the exception of slight prolongation of the P1 wave, we found no significant variation in any response measure. Intraclass correlation analysis revealed that the speech-evoked FFR amplitude and latency measures achieved superior repeatability (intraclass correlation coefficient .0.85) among the more widely used obligatory brainstem (ABR) and cortical (P1-N1-P2) auditory-evoked potentials. Contrasting these intersubject effects, intrasubject variability (i.e., within-subject coefficient of variation) revealed that while latencies were more stable than amplitudes, brainstem and cortical responses did not differ in their variability at the single subject level. Conclusions: We conclude that (1) the variability of auditory neural responses increases with ascending level along the auditory neuroaxis (cortex.brainstem) between subjects but remains highly stable within subjects and (2) speech-FFRs might provide a more stable measure of auditory function than other conventional responses (e.g., click-ABR), given their lower inter- and intrasubject variability

Isokinetic strength and anaerobic power of elite, subelite and amateur French soccer players.

Information about the influence of different practice levels on physical characteristics of a large number of soccer players is lacking. Therefore we assessed muscular strength and anaerobic power of elite, subelite and amateur soccer players to clarify what parameters distinguish the top players from the less successful. We tested 95 soccer players from the French first division (elite), second division (subelite), and amateurs and determined the isokinetic strength of the knee extensor and flexor muscles at angular velocities from -120 degrees x s(-1) to 300 degrees x s(-1). Vertical jump, 10 m sprint, 30 m sprint and maximum ball speed during shooting were also measured. The elite players had higher knee flexor torque than the amateurs at all angular velocities (p < 0.05), except at 300 degrees x s(-1). The hamstring/quadriceps ratios proposed with two different methods were significantly lower in the amateur group than in the elite group (p < 0.05), except at 300 degrees x s(-1). Maximum ball speed during shooting and speed over 30 m sprint were not different between elite, subelite, and amateur players while speed over a 10 m sprint was significantly slower in amateur players and faster in the elite group (p < 0.05). Although performance in soccer is not determined only by measurable variables, professional players differ from amateurs in terms of knee flexor muscle strength and short-distance sprinting speed. Based on these findings we conclude that hamstring strength is extremely important in soccer players for joint stabilization during various tasks, notably in eccentric action. Further, short-sprinting performance may mirror actual game situations at high level and could be an important determinant of match-winning actions

Strength and power changes of the human plantar flexors and knee extensors in response to resistance training in old age

Aim: The aim of the present study was to assess and compare the improvements of muscle strength and power induced by a 16-week resistive programme in a population of 16 older men aged 65-81 years. Methods: Training was performed three times per week at an intensity of 80% of one repetition maximum (1RM) and consisted of both calf raise and leg press exercises. Before-, during- and after-training, maximum isometric and isokinetic torques, maximum power, 1RM, muscle cross-sectional area (CSA) and electromyographic activity (EMG) of the plantar flexors (PF) and knee extensors (KE) were examined. Results: For the KE and PF, respectively, training resulted in a 29.9 \ub1 4.4% (mean \ub1 SE) and 21.6 \ub1 5.4% increase in 1RM (P < 0.001-0.01), a 19.4 \ub1 4.3 and 12.4 \ub1 4.7% (P < 0.001-0.05) increase in maximum isometric torque, and a 24.1 \ub1 6.3 and 33.1 \ub1 10.9% (P < 0.05) increase in maximum muscle power, calculated from torque-angular velocity curves. The large increase in torque and power was partly accounted by a significant increase in the CSA of the PF (5.0 \ub1 0.7%) and KE (7.4 \ub1 0.7%), while no significant changes in integrated EMG activity of vastus lateralis and soleus muscles, and in extrapolated maximum shortening velocity were found. After training, a significant increase in torque/CSA (10.3 \ub1 4%, P < 0.05) was found for the KE but not for the PF. Conclusion: Hence, hypertrophy cannot alone justify the increase in torque, and other factors, such as an increase in individual fibre-specific tension (in the case of KE), a decrease in antagonist muscles' coactivation, an improved co-ordination and an increased neural drive of the other heads of quadriceps may have contributed to the increments in strength. The significant increase in muscle power seems particularly noteworthy with respect to daily activities involving the displacement of the body over time, namely, the generation of muscle power