Isometric Contraction

Lower extremity overuse injuries are associated with gluteus medius (GMed) weakness. Understanding the activation of muscles about the hip during strengthening exercises is important for rehabilitation. To compare the electromyographic activity produced by the gluteus medius (GMed), tensor fascia latae (TFL), anterior hip flexors (AHF), and gluteus maximus (GMax) during 3 hip-strengthening exercises: hip abduction (ABD), hip abduction with external rotation (ABD-ER), and clamshell (CLAM) exercises. Controlled laboratory study. Laboratory. Twenty healthy runners (9 men, 11 women; age = 25.45 ± 5.80 years, height = 1.71 ± 0.07 m, mass = 64.43 ± 7.75 kg) participated. A weight equal to 5% body mass was affixed to the ankle for the ABD and ABD-ER exercises, and an equivalent load was affixed for the CLAM exercise. A pressure biofeedback unit was placed beneath the trunk to provide positional feedback. Surface electromyography (root mean square normalized to maximal voluntary isometric c...

To date, there have been very few studies on the age dependence of maximal isometric muscle strength (MIMS) in healthy subjects aged 20–80 years, based upon measurements of a large number of functional muscle groups (FMGs). Using a hand-held pull gauge it is possible to measure MIMS of nearly every FMG. The objectives of this study were to obtain normative values for MIMS, to evaluate differences in MIMS in relation to gender and body side and to compare the age dependence of muscle strength between women and men. In a convenience sample of 290 healthy women (aged 20–82 years) and 253 men (aged 21–79 years), MIMS of 51 FMGs was measured. For each FMG the age dependence of MIMS was depicted, side and gender specific, as percentile curves and was analysed using linear quantile regression analysis. MIMS was found to be significantly higher in men than in women and higher on the right than on the left side. A biphasic model with linear equations for strength medians was derived for each gender. The age at transition from phase 1 to phase 2 was 55 years (SD 8) for women and 49 years (SD 13) for men. During phase 1, MIMS did not decrease significantly. During phase 2, MIMS decreased in all FMGs in both genders with a steeper slope in women (−0.92) than in men (−0.63). The age dependence of MIMS differed significantly between women and men. The present study gives gender-specific equations which enable one to calculate normative values for MIMS, as measured with a pull gauge, based upon age. These normative values will allow an objective assessment of patients with diminished muscle strength as, for example, in myositis, rheumatoid arthritis and nerve root compression syndromes or in the elderly.

In this article, the authors examined the hypothesis that the direction of the change (increase or decrease) in the dynamical degrees of freedom (dimension) regulated as a function of motor learning is task-dependent. Adult participants learned 1 of 2 isometric force-production tasks (Experiment 1: constant force output; Experiment 2: sinusoidal force output) over 5 days of practice and a 6th day with augmented information withdrawal. The results showed that over practice, the task goal induced either an increase (Experiment 1) or a decrease (Experiment 2) in the dimension of force output as performance error was reduced. These findings support the proposition that the observed increase or decrease in dimension with learning is dependent on both the intrinsic dynamics of the system and the short-term change required to realize the task goal.

The purposes of this review are to identify the factors that contribute to the transference of strength and power training to sports performance and to provide resistance-training guidelines. Using sprinting performance as an example, exercises involving bilateral contractions of the leg muscles resulting in vertical movement, such as squats and jump squats, have minimal transfer to performance. However, plyometric training, including unilateral exercises and horizontal movement of the whole body, elicits significant increases in sprint acceleration performance, thus highlighting the importance of movement pattern and contraction velocity specificity. Relatively large gains in power output in nonspecific movements (intramuscular coordination) can be accompanied by small changes in sprint performance. Research on neural adaptations to resistance training indicates that intermuscular coordination is an important component in achieving transfer to sports skills. Although the specificit...