The data indicate that with repetition of maximal voluntary eccentric contractions, there is an increased activation of slow motor units and a concomitant decrease in activation of fast units.
The objective of this study was to find out whether basal and/or active energy metabolism are altered in isolated mouse extensor digitorum longus muscle injured by eccentric (Ecc) contractions. Measurements of basal O2 consumption and isometric tetanus O2 recovery cost were made at 25 degrees C on muscles that had done either 10 Ecc, 10 isometric (Iso), or no contractions (No). In parallel experiments, rates of lactate and pyruvate production were measured to estimate the anaerobic contribution. Basal O2 consumption was unaffected by the type of protocol performed (P = 0.07). However, the tetanus O2 cost per force-time integral was elevated by 30-36% for the Ecc protocol muscles over that for the Iso and No protocol muscles. When including the increased lactate production by the Ecc protocol muscles, the total energetic cost per force-time integral was 53% higher than that for the Iso protocol muscles [2.35 +/- 0.17 vs. 1.54 +/- 0.18 mumol O2/(N.m.s)]. The decreased economy was attributed to two factors. First, in skinned fibers isolated from the injured muscles, the ratio of maximal actomyosin adenosinetriphosphatase activity to force production was up by 37.5%, suggesting uncoupling of ATP hydrolysis from force production. Second, increased reliance on anaerobic metabolism along with the fluorescent microscopic study of mitochondrial membrane potential and histochemical study of ATP synthase suggested an uncoupling of oxidative phosphorylation in the injured muscles.
Background and Purpose. Little is known about the relationship among impairments, functional limitations, and disability in people with cervical spine disorders (CSD) despite the fact that these concepts are routinely used in clinical practice. The primary purpose of this study was to investigate the relationships among commonly assessed impairment, functional limitation, and disability measures in patients with CSD. A secondary purpose was to determine the influence of payment source and time since onset of symptoms on these same measures. Subjects. Eighty patients (mean age=45.7 years, SD=15.9, range= 20–88) with CSD who were referred for physical therapy participated in the study. Methods. Data were obtained for 3 measures of impairment, 2 measures of functional limitation, and 3 measures of self-reported disability during the initial visit. Results. All 3 sets of variables (ie, impairment, functional limitation, disability) correlated with each other, with the highest correlation occurring between the impairment measures and the functional limitation measures (r=.82). Other correlations were noted between individual variables. There was no effect of payment type or time since onset of symptoms on the variables. Conclusion and Discussion. Positive correlations were noted among the 3 sets of measures, which supports the assumption that impairments, functional limitations, and disability are related in patients with CSD.
Eccentric contractions using the trunk extensor muscles result in higher levels of multifidus EMG activity to produce a given level of torque. This reduction in neuromuscular efficiency persisted for one day with recovery to baseline levels by the third day. Contrary to studies using other muscle groups, no sustained alteration in muscle function was observed.
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