Isokinetic isometric

Data suggest that extensive physical exercise may increase blood plasma TAC. Long-term effects of systematic physical exercise are, however, controversial. Sub-maximal exercise (30 min) was reported not to alter blood plasma TAC significantly (A7). TAC of blood plasma was reported to increase immediately after a marathon run (by 25%) and this increase persisted 4 days later (by 12%) (L19). Similar effects (increase by 19%) were noted after a half-marathon (C29). Another study reported an increase in blood serum TAC by 22% during a 31-km run and by 16% during a marathon (V10). TAC of blood plasma was increased by 25% after a maximum aerobic exercise test and by 9% after a nonaerobic isometric exercise test (A8). Eccentric muscle exercise (70 maximal voluntary eccentric muscle actions on an isokinetic dynamometer, using the knee extensors of a single leg) did not affect blood serum TAC (C27). In another study, TAC increased after exhaustive aerobic (by 25%) and nonaerobic isometric exercise (by 9%) (A8). 

Karwowski, W., and Pongpatanasuegsa, N. (1988), Testing of Isometric and Isokinetic Lifting Strengths of Untrained Females in Teamwork, Ergonomics, Vol. 31, pp. 291-301. 

Yet another method used to reflect endurance is to calculate an endurance-related work ratio. Many isokinetic testing devices, such as the one shown in Figure 76.3b, will calculate work (integrate force or torque over displacement). In this case, the total amount of work performed in the first five repetitions is compared with the total amount of work performed in the last five repetitions of a series of repetitions (usually 25 or more). Work degradation reflects endurance and is reported as percentage. An additional limitation of using these endurance ratios is that work cannot be determined in isometric test protocols. Mechanically there is no movement, and no work is being performed. 

FIGURE 6.26 Resultant force in the ACL for isometric (thick line) and isokinetic (30, 90, 180, and 300 deg/sec) knee-extension exercises. The results were obtained from a two-dimensional model of the knee joint, assuming the quadriceps are fully activated and there is no cocontraction in the flexor muscles of the knee (Serpas et al in press). The model results show that exercises in the studied speed range can reduce the force in the ACL by as much as one-half. [Modified from Serpas et at. (in press. ]... 

The forces exerted between the femur and patella and between femur and tibia depend mainly on the geometry of the muscles that cross the loiee. For maximum isometric extension peak forces transmitted to the patellofemoral and tibiofemoral joints are around 11,000 N and 6500 N, respectively (i.e., 15.7 and 9.3 times body weight, respectively) (Fig. 6.27). As the knee moves faster during isokinetic extension exercise, joint-contact forces decrease in dire proportion to the drop in quadriceps force (T. Yanagawa and M. G. Pandy, unpublished results). 

Isokinetic exercise increases the work a muscle can do more rapidly than either isometric or isotonic exercise. It is more efficient. Isometric exercise should be used when motion of the joint is contraindicated or creates pain. For skill training, the best form of exercise is isotonic repetition of the motiorts needed in performing those skills. 

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