Isokinetics and Exercise Science

Article without abstract.

Within the conceptual framework of muscular imbalances (MI) it is commonly assumed that altered muscle performance characteristics (i.e. strength deficits) are associated with a higher risk of overuse or traumatic injury or re-injury. However, scientific literature reveals several difficulties which question the general adequacy of this framework.

According to recent lines of evidence it seems that 1) quantification of balance of muscle performance is problematic and hence classification of an imbalanced muscle function is also difficult 2) a clear system which is able to differentiate between normal (balanced) or abnormal(imbalanced) muscle performance cannot be established universally 3) it is still not evident if and to what extent a relatively higher increase of function of prime movers predisposes an athlete to a higher risk of injury 4) assessment of muscle function in relation to the onset of musculoskeletal disorders has to be based on several aspects of muscle function; single-factor-related analysis (e.g. uniplanar strength ratio) reflects an insufficient approach.

As a consequence, this paper recommends a preliminary alternative approach in an attempt to assess muscle function in relation to both performance and injury prevention and muscular recovery after injury. Within a multifactorial approach, detailed qualitative and quantitative observations should reveal if arthro-neuromuscular function is in a state of adaptation, de-adaptation or compensation and if joint function and/or whole body mechanics are limited. In addition, emphasis has to be put on the importance of the transfer of the results into structured treatment strategies.

Article without abstract.

An inertia-based ergometer is among the latest devices suggested to abate space flight-induced muscle deconditioning. The current study uses separate sets of subjects to assess net caloric cost (n=14) and electromyography (EMG) (n=46) responses to leg presses done on the ergometer. All subjects performed the eight-repetition protocol three times over a two-week period. Net caloric cost measurements entailed indirect calorimetry from O $_2$ uptakes resulting from exercise on the ergometer. EMG subjects provided first and eighth repetition work, root mean square (RMS) and mean power frequency (MPF) data. Work output was more correlated to net caloric cost (r=0.83, p<0.05) than were anthropometric variables. EMG subject data showed work had gender-by-muscle-action and repetition-by-muscle-action effects, with male concentric and first repetition concentric data responsible the respective interactions. From the first to the eighth repetition, eccentric work incurred insignificant changes. RMS had a repetition-by-muscle-action effect, with eighth eccentric repetition data the source of the interaction. MPF showed an effect for repetition (eighth < first). In lieu of significant eighth-repetition RMS and MPF changes, high-threshold lengthening motor unit recruitment and/or greater series elastic element activity may explain the lack of eccentric work losses.

Passive stiffness (Nm/°) of the plantar flexors was measured during a passive stretch into dorsiflexion (DF) in 18 healthy female subjects(range 18–60 years old) using an isokinetic dynamometer. Passive stiffness of the ankle joint was measured at a short range of motion (from 10° of plantar flexion (PF) to 10° of DF), and at a full range of motion (from 10° PF to maximal DF for each individual) with a neutral EMG from a subset of four legs. The purpose of the study was to assess the variances in the measurements of passive stiffness of the calf muscle and to correlate passive stiffness to age and jumping ability. There was a significant correlation (r=0.76) between the FRS and FRS test-retest. The methodological error for duplicate determinations was 7.7% for the SRS and 5.5% for the FRS. There was a significant correlation between age and the (FRS) full-range stiffness (r=0.83). There was a significant negative correlation between age and jumping (r=−0.54). We conclude that the test model of passive stiffness used in the present study is a useful method with good reliability. The passive elastic properties of muscles and tendons might explain part of the muscle performance in functional tests with ageing. However, other qualities may influence performance as well.

The purpose of this study was to compare the dynamic elastic and static viscoelastic stress-relaxation (VSR) properties of the calf muscle-tendon unit (MTU) between men and women. A Kin-Com® dynamometer moved the ankle of 15 men and 14 women (age range 23–35 years) from plantarflexion to maximal dorsiflexion (DF) at 5°/s with negligible surface electromyogram activity to measure the dynamic passive elastic properties. The ankle was then moved to three DF angles defined at 100%, 90% and 80% of the maximal DF force and held for 60 s each to measure the static VSR as the torque decline. ANOVA procedures indicated that the men had greater absolute dynamic maximal passive DF torque, full stretch mean torque, absorbed passive elastic energy (area under the curve) and passive elastic stiffness through the full stretch and through the last 10° of the stretch (P⩽0.014). All but the full stretch stiffness remained significantly greater when controlled for body mass (P⩽0.042). The absolute torque decline for the three static stretches showed significant group, time and interaction effects (P<0.001). The percent torque decline during the first 15 s of static stretch, normalized to the total percent decline (100%) was greater for men at the 90% (P=0.049) and 80% (P=0.036) stretch angles. The results indicated that the calf MTU of men has greater dynamic elastic and static VSR properties than women, which may influence ambulatory functional activities and adaptations to therapeutic stretching.

The aim of the present study was to investigate whether cycle training offers an effective means for improving muscle strength in young people, as strength training has been recognized as safe and effective in improving muscle strength. Nineteen 13-year-old and eighteen 16-year-old boys formed the training group, while the control group was formed by eighteen 13-year-old and twenty 16-year-old boys. Participants took part in a strength-training program involving cycle training 3 times per week for a period of 12 weeks, whereas controls participated only in the school's physical education activities. Maximum knee extension and flexion was evaluated at various angular velocities, as well as local muscular endurance of extensors using an isokinetic dynamometer. With regard to the training group, significant increases (p<0.001) were observed for both extensors and flexors in all angular velocities, as well as for local muscular endurance of extensors, for both age groups (p<0.001). However, for the control group significant increases were observed only in high angular velocities(180°·s $^{-1}$ , 300°·s $^{-1}$ ) (p<0.05 to p<0.001) in both age groups. The findings suggest that the specific cycle training protocol used in this study is an effective means for improving muscle strength training and local muscular endurance in pubescent and postpubescent untrained males.

The purpose of this study was to investigate the reproducibility of findings derived from a new iso-inertial dynamometer during bench press (BP) and squat (SQ) and to provide descriptive data for recreational athletes. A position transducer and accelerometer were combined to assess velocity and power during free weight lifting exercises. Simulated movement with a pulley system revealed the excellent technical consistency of the dynamometer. Sixteen male subjects participated in the study. Iso-inertial tests consisted of lifting as fast as possible four different relative loads (35, 50, 70, 90% 1RM in BP and 45, 60, 75, 90% 1RM in SQ). The test was repeated one week later. Analysis of variance revealed no significant variation between sessions or trials. Reproducibility was better in velocity than in power, although it remained fairly good in both exercises (coefficients of variation [CV] never exceeding 10%) except for the time to peak power parameter. Descriptive data confirmed the classical force-velocity and force-power relationships for BP and SQ. In conclusion, this study demonstrated reliable measurements in BP and SQ iso-inertial exercises. Monitoring force-velocity and force-power relationships offers an original functional approach in strength training supervision.

The aim of this study was to determine if inter-individual differences in crank torque production and/or pedalling effectiveness influence the variations of muscular efficiency observed among subjects in cycling. Eleven subjects performed a 5 minutes steady state cycling at 160 Watts at 80 revolutions per minute. Gross (GE) and net (NE) muscular efficiency, angular impulses and pedalling effectiveness during the whole pedal revolution(IE $_{360}$ ) and during the downstroke phase(IE $_{180}$ ) were investigated. Angular impulses were not related to either �O $_2$ or the muscular efficiency. IE $_{360}$ was not correlated with either�O $_2$ or muscular efficiencies, while IE $_{180}$ was significantly negatively correlated with�O $_2$ (r $^2$ =0.51) and positively related with NE (r $^2$ =0.49). The inter-individual differences in crank torque production, as investigated by angular impulse values, did not explain inter-individual differences in muscular efficiency. The lack of relationships between �O $_2$ or muscular efficiencies and IE $_{360}$ could be due to the fact that IE $_{360}$ is equally influenced by both low and high pedal forces produced during the upstroke and downstroke phases, respectively, while metabolic energy is mainly consumed during high pedal forces of the downstroke phase. Finally, when measured during the downstroke phase, inter-individual differences in pedalling effectiveness could partly be related to the variations of muscular efficiency observed among subjects in cycling.

Achilles tendinopathy is a common overuse injury in athletes, especially older athletes. This condition is difficult to treat and often becomes chronic. This evidence based review summarized the current pathophysiological principles guiding research as well as clinical practice and synthesized the search results to determine if eccentric exercises were effective in the treatment of patients with Achilles tendinopathy. Seven studies were identified, but only two were randomized clinical trials (level A evidence) with the rest controlled clinical studies or prospective cohort studies (level B evidence). Only one study reported follow-up one year beyond the intervention period. Based on a crossectinal analysis of post treatment outcomes, there was modest but significant clinical benefits following eccentric exercise training, but insufficient evidence to predict the long-term effects of eccentric exercise training for the management of Achilles tendinopathy. Although randomized clinical trials with a large subject population are still needed, eccentric exercise paired with biomedical training techniques should be integrated into treatment guidelines for patients with Achilles tendonitis.

Muscle strength and balance around the lower limb joints may play an important role for performance and injury prevention in basketball. The purpose of this study was to examine isokinetic "functional" and "conventional" torque ratios around the ankle joint in young basketball players. One hundred and eighty males from 12 to 17 years old (30 persons per age group) performed maximum concentric and eccentric efforts of the plantar and dorsiflexors at 30°·s $^{-1}$ and 90°·s $^{-1}$ . Three-way analysis of variance (ANOVA) designs indicated that the absolute isokinetic plantar and dorsiflexion strength increased(p<0.05) from 12 to 15 years and then demonstrated a plateau until 17 years old. When the isokinetic strength was normalized relative to body mass the only difference was found between the 16–17 and 12–13 year-olds. Two-way ANOVAs indicated non-significant effects of chronological age on all reciprocal muscle group ratios suggesting uniformity in the development of peak isokinetic torque of plantar and dorsiflexors throughout the developmental ages. Coaches and physical therapists may use this information when evaluating and planning exercise programs of ankle musculature during training and rehabilitation.