Boundary line between the strength and endurance regions in manual lifting

Previous work by Mital et al. showed that repetitive dynamic strength (RDS) of individuals is a better predictor of psychophysically acceptable weight (PAW) than either the maximal dynamic strength (MDS) or maximal static strengths (MSSs). It was also pointed out that somewhere between a frequency of one lift per minute and a frequency of three lifts per minute, the orientation of lifting tasks changes and muscular strengths no longer remain the limiting factor. This paper reports the results of a follow-up study conducted to pinpoint the lifting frequency just beyond which this transition takes place. The results indicated that a significant correlation existed between RDS and PAW for lifting frequencies up to 1·5 lifts per minute. Beyond 1·5 lifts per minute, no significant correlation between the two measures was found. We therefore concluded that lifting tasks performed every 40 seconds, or less frequently, are strength oriented. For those tasks which require lifting more frequently than once every 40 seconds, individual's strengths are not a limiting factor.