A work-energy approach was used to determine the contributions of the muscles crossing the hip, knee and ankle joints to the total positive work done during maximal vertical jumps. It was found that the average relative contributions of the ankle and hip muscles were approximately 23 and 28% respectively, with the remaining 49% of the work being done by the muscles acting at the knee joint. The efficiency of jumping, i.e. the ratio of potential energy gained to the net mechanical work done by the muscles acting at the three lower limb joints was nearly 1.0. These results stress the importance of all three major leg extensor muscle groups to the performance of an explosive activity such as vertical jumping. It is suggested that the work-energy approach supplies useful information concerning joint contributions without the problems associated with other techniques.

Internal mechanical work during cycling, required to raise and lower the legs and change their velocities, is shown to be an important factor when interpreting physiological responses to cycle ergometer exercise. The internal work required to move the legs during concentric and eccentric cycle ergometry at different speeds and workloads was calculated from segmental energy changes determined using cinematography and directly using an eccentric ergometer. The mean internal work rates obtained at pedal frequencies of 30, 60 and 90 min-1 were 11.5, 20 and 62 W respectively. When these estimates were added to the external work rates, they increased concentric and decreased eccentric work rates. The largest differences were seen at low work rates and high pedal frequencies during which concentric work rates increased by 51% and eccentric decreased 60% by the inclusion of internal work. When comparisons of concentric and eccentric cycling at equal uncorrected work rates were made, neglecting to include internal work introduced errors ranging from 12 to 97%. The calculated estimates of internal work agreed well with the power supplied by the eccentric ergometer to move the legs passively. The investigations show that the inclusion of internal work is important when comparing physiological responses during concentric and eccentric ergometry, especially when pedal frequencies exceed 60 min-1 and when work rates are small.

The use of constant velocity dynamometers in functional testing and in exercise and therapy programs has been increasing in the past few years. For movements in the horizontal plane there are no gravitational errors. However, in vertical movements the limbs are not only working against the dynamometer but also are either aided or opposed by gravity. Far too often these gravitational forces have not been taken into account, and the error involved can be quite large. 1. A study on four subjects using knee extension (against gravity) and flexion (with gravity) showed the error in mechanical work to vary from 26-43% in extension and from 55-510% in flexion. 2. A relatively simple solution is offered to overcome the problem by compensating for the gravitational errors over the full range of movement. The time course of the error is such as to cause erroneous magnitudes of recorded moments which are a maximum at low level contractions and minimum at high level contractions. 3. The effect of gravitational and other acceleration errors are such as to cause false early peaks in the muscle moment curves resulting in erroneous conclusions about muscle function.

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