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The authors discuss fiber typing and morphologic changes resulting from training and how these affect athletic performance. Also considered is the concept of strength, its measurement and development, and how strength affects athletic performance, activity, and injury.
Recovery of maximal force and power following a 10-km race has not been widely studied in the scientific literature. Ten healthy men who were experienced distance runners participated in this investigation. Data were collected prerace, immediate postrace, and 48 hours postrace to examine the effect of a 10-km race on muscle force production in the lower body. Maximal peak torque was measured via an isokinetic dynamometer at 30 degrees, 180 degrees, and 300 degrees.s-1. A significant (p <or= 0.05) reduction in peak torque for knee flexion was observed at 30 degrees.s-1 immediately postrace. Average power of the knee flexors were significantly decreased immediately postrace. Total work (J) flexion performed over the last 17 repetitions of the 50-repetition test were significantly reduced from baseline values during both the immediate and 48-hour postrace tests. Significant reductions in peak vertical jump force remained reduced 48 hours postrace testing. No changes were observed for jump power after the race. These data indicate that only the hamstring muscle group was not fully recovered to perform the 50-repetition test and that force production in the vertical jump test was compromised 48 hours after a 10-km race. Nevertheless, it appears that strength and power capabilities of the 10-km runner are for the most part restored 48 hours after an all-out 10-km race effort. From a practical perspective, it appears that a minimum of 48 hours should be utilized between multiple trials in 10-km races at track and field meets.
A prospective, randomized clinical trial was conducted to compare an intra-articular with an extra-articular reconstruction of the anterior cruciate ligament. Isokinetic muscle testing was carried out 6 months to 2 years following operation using the Biodex isokinetic dynamometer. The extra-articular procedure resulted in a lower deficit for the peak quadriceps and hamstring torques and the range of motion.
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The study aimed to evaluate the effect of low-intensity night-time therapeutic electrical stimulation (TES) on arm strength and function in children with intermediate type spinal muscular atrophy (SMA). The design was a randomized controlled trial with a 6-month baseline control period. Children were evaluated at baseline, 6, and 12 months. TES was applied from 6 to 12 months to the deltoid and biceps muscle, of a randomly selected arm with the opposite arm receiving a placebo stimulator. Thirteen individuals with SMA between 5 to 19 years of age were recruited into the study and eight completed the 12-month assessment. No statistically significant differences between the treatment and control arm were found at baseline, 6, and 12 months for elbow flexors, or shoulder abductors on quantitative myometry or manual muscle testing. There was no significant change in excitable muscle mass assessed by M-wave amplitudes, nor function on the Pediatric Evaluation of Disability Inventory (self-care domain). Therefore, in this study there was no evidence that TES improved strength in children with SMA.
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This study was launched to establish the profile of knee dynamic concentric strength in elite male gymnasts after it was found that three of the 10-member Canadian men's gymnastics team had incurred anterior cruciate ligament (ACL) rupture. The dynamic concentric force characteristics of the quadriceps and hamstring muscles of 84 male gymnasts were studied at the Canadian National Championships using a Kin-Com isokinetic dynamometer. These tests were performed at 90 degrees/sec and 230 degrees/sec and revealed that the hamstrings to quadriceps peak torque ratio was not only unusually low (0.5) when compared with data collected in previous research, but that this ratio was consistent across all ages, from 12 to 27 years. The torque ratios were also reported at 30 degrees, 45 degrees, and 60 degrees and it was found that the ratios decreased as the joint angle increased and again was consistent across the four age groups. It was also found that the hamstrings to quadriceps peak torque ratio did not increase (hamstrings becoming stronger relative to quadriceps) as velocity of movement increased as has been reported in other studies. It was hypothesized that the large shear forces that are generated about the knee in gymnastics (extrinsically from backward landing and intrinsically from the quadriceps eccentrically contracting), combined with the relatively weak hamstrings, could be one cause for the increasing incidence of ACL injuries in that sport. The results of this study indicate that it would be prudent for clinicians involved with gymnasts to test for knee strength imbalance and to prescribe exercises to correct it when necessary.
The purpose of this investigation was to compare children and adults of both genders with respect to torque-velocity, electromyogram (EMG)-velocity and torque-EMG relationships during maximal voluntary knee extensor muscle actions. Four groups of ten subjects each were studied comprising 11-year-old girls and boys and female and male physical education students (22-35 years). Maximal voluntary eccentric (lengthening) and concentric (shortening) actions of the knee extensors were performed at the constant velocities of 45, 90 and 180 degrees.s-1. Average values for torque and EMG activity, recorded by surface electrodes from the quadriceps muscle, were taken for the mid 40 degrees of the 80 degrees range of motion. The overall shapes of the torque- and EMG-velocity relationships were similar for all four groups, showing effects of velocity under concentric (torque decrease and EMG increase) but not under eccentric conditions. Eccentric torques were always greater than velocity-matched concentric ones, whereas the eccentric EMG values were lower than the concentric ones at corresponding velocities. Torque output per unit EMG activity was clearly higher for eccentric than for concentric conditions and the difference was of similar magnitude for all groups. Thus, the torque-EMG-velocity relationships would appear to have been largely independent of gender and to be fully developed at a prepubertal age.
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