Dynamic analysis of isoinertial lifting technique.

The objectives of the study were threefold: (1) to quantify dynamic measures (displacement, velocity, force/acceleration, and power) of a 1·83 m isoinertial lift on an incremental lifting machine (ILM); (2)to identify any gender differences in ILM lifting technique; and (3) to assess the implications of these data for the use of the ILM as a screening device. One hundred and thirty-two military personnel (33 females and 99 males) completed a maximal isoinertial lifting test from a starting height of 0·34 m to a target height of 1·83 m on the ILM. A force transducer attached to the back of the armature provided continuous velocity and displacement data from which the displacement, velocity, acceleration/force, and power profiles were determined. These data were summarized into 37 lift parameters; 33 representing the dynamic components of the lift, and four representing averages taken across the entire lift. The results revealed that the 1·83 m isoinertial lift could be described in three phases: (1) a powerful pulling phase, which incorporated measures of maximal acceleration/force, velocity, and power; 2) a wrist changeover manoeuvre, wherein momentum was required to compensate for minimal force and acceleration values; and (3) a pushing phase, during which second maximal force and acceleration measures were attained. Statistically significant differences were found between genders on various parameters of the technique profiles, suggesting that the testing protocol may have placed different demands on males and females. Females spent a greater proportion of the total lift time in the pushing phase, and had less opportunity to generate power during the pulling phase. The resulting TLM scores may have underestimated the lifting capacity of females. It was recommended that females and males be given independent consideration in the design of ILM lifting protocols.