Knee Muscles Power Evolution in Patients with Total Knee Arthroplasty
OBJECTIVES Peak torque expresses a point output which may, but does not always, correlate well with full range output measures such as work or power, particularly in a rehabilitating muscle. This study evaluates isokinetic performance variables, particularly (a) flexor to extensor work and power output ratios of upper and lower extremities and (b) overall upper to lower extremity work and power ratios, in intercollegiate athletes. The purpose was to ascertain how speeds of 30 and 180 degrees/s influence agonist to antagonist ratios for torque, work, and power and to determine the effects of these speeds on upper to lower limb flexor (F), extensor (E), and combined (F + E) ratios, as a guide to rehabilitation protocols and outcomes after injury. METHODS Twenty seven athletic men without upper or lower extremity clinical histories were tested isokinetically at slow and moderately fast speeds likely to be encountered in early stages of rehabilitation after injury. Seated knee extensor and flexor outputs, particularly work and power, were investigated, as were full range elbow extensor and flexor outputs. The subjects were morphologically similar in linearity and muscularity (coefficient of variation 4.17%) so that standardisation of isokinetic outputs to body mass effectively normalised for strength differences due to body size. Peak torque (N.m/kg), total work (J/kg), and average power (W/kg) for elbow and knee flexions and extensions were measured on a Cybex 6000 isokinetic dynamometer. With respect to the raw data, the four test conditions (F at 30 degrees/s; E at 30 degrees/s; F at 180 degrees/s; E at 180 degrees/s) were analysed by one way analysis of variance. Reciprocal (agonist to antagonist) F to E ratios of the upper and lower extremities were calculated, as were upper to lower extremity flexor, extensor, and combined (F + E) ratios. Speed related differences between the derived ratios were analysed by Student's t tests (related samples). RESULTS At the speeds tested all torque responses exhibited velocity related decrements at rates that kept flexor to extensor ratios and upper to lower extremity ratios constant (p > 0.05) for work and power. All upper extremity relative torque, work, and power flexion responses were equal to extension responses (p > 0.05) regardless of speed. Conversely, all lower extremity relative measures of torque, work, and power of flexors were significantly lower than extensor responses. In the case of both upper and lower extremities, work and power F to E ratios were unaffected by speed. Moreover, increasing speed from 30 to 180 degrees/s had no effect on upper to lower extremity work and power ratios, whether for flexion, extension, or flexion and extension combined. CONCLUSIONS Peak torque responses may not adequately reflect tension development through an extensive range of motion. Total work produced and mean power generated, on the other hand, are highly relevant measures of performance, and these, expressed as F to E ratios, are unaffected by speeds of 30 and 180 degrees/s, whether for upper or lower extremities or for upper to lower extremities. In this sample, regardless of speed, the upper extremity produced 55% of the work and 39% of the power of the lower extremity, when flexor and extensor outputs were combined. Injured athletes are, in the early stages of function restoration, often not able to exert tension at fast speeds. An understanding of upper to lower extremity muscular work and power ratios has important implications for muscle strengthening after injury. Knowledge of normal upper to lower extremity work and power output ratios at slow to moderately fast isokinetic speeds is particularly useful in cases of bilateral upper (or lower) extremity rehabilitation, when the performance of a contralateral limb cannot be used as a yardstick.