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Restitution of the EMG spectrum was studied in upper limb muscles. The subjects performed isometric and isotonic exercises until they refused because of fatigue. Force levels varied from 15 to 60% MVC. The mean frequency was used as an indicator of the modification of the spectrum. Restitution of the EMG spectrum was studied by recording for 10 min after the end of the fatigue experiment at intervals of 1 to 3 minutes. Recovery was rapid at the beginning, levelling off to a plateau in 2 to 5 min. The change was more regular in isometric experiments than in kinetic ones, although interindividual differences were large in both cases.

Intraabdominal pressure (IAP), movements of the body in the sagittal plane, and the forces applied to the load were recorded while 10 male subjects lifted or lowered a 15-kg box using six different lifting techniques and two lowering techniques. IAP data were compared with calculated peak values of lifting velocity, lumbosacral compression and hip torque, and with the integral of lumbosacral compression over time. No consistent relationship between IAP increases and any one of these values emerged. The variation in peak IAPs was considerable. Nonetheless, there were significant differences in IAP between different lifting and lowering techniques. IAP was, in general, less when the trunk was flexed for lifting and lowering than when it was used in a posture nearer to the vertical.