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Maximum isometric lifting strengths of men in teamwork.

Article Excerpt
INTRODUCTION

Human strength is extensively used for operating equipment or moving objects. The evaluation of human strength is necessary for matching the muscular capability of workers with the force requirement for a particular job and for developing ergonomic guidelines for preemployment screening of workers. Measurements of human isometric, isokinetic, and isoinertial strengths have already been developed previously. These three strengths refer to a buildup of tension in the muscle with no actual movement, at a controlled velocity, and against a constant inertia, respectively. These strength measurements are useful in industrial settings, depending on the required working tasks, for determining the maximum permissible level of load to be handled.

In practice, for workers to complete their assignments, teamwork is popular when the handled objects are too heavy or bulky. However, only limited information is available in the literature for teamwork strength. In 1927 Walther Moede, an industrial psychologist, reported the first study on collective teamwork strength obtained by his student Ringelmann. Ringelmann observed that when teams of coworkers pulled on a rope, their collective teamwork strength was inferior to the sum of their individual strengths (Ingham, Levinger; Graves, & Peckham, 1974). Ingham et al. confirmed the decrement for teamwork strength on rope-pulling tasks experimentally and showed that the addition of a fourth, fifth, or sixth member to the team produced insignificant additional decrements in teamwork strength.

Some information regarding the additivity for teamwork lifting strength was demonstrated. Karwowski and Mital (1986) and Karwowski and Pongpatanasuegsa (1988) revealed that human isometric and isokinetic teamwork lifting strengths for two-person and three-person teams were not additive. The teamwork lifting strength as the percentage of the sum of the individual lifting strengths (%sum) was significantly less than 100% for male and female participants, with the exception of some isometric strengths. Rice, Sharp, Nindl, and Bills (1995) developed regression equations to predict the maximum isoinertial two-person teamwork lifting strength from the floor to knuckle height, indicating that teamwork lifting strength was dictated by the weaker of the two members.

Sharp and colleagues (Sharp, Rice, Nindl, & Mello, 1995; Sharp, Rice, Nindl, & Williamson, 1993a, 1993b, 1997) investigated the effects of gender on %sum for isoinertial teamwork lifting and carrying tasks, indicating that %sum for male teams was less than that for female teams and that for single-gender teams it was greater than that for mixed-gender teams. Sharp et al. (1997) also demonstrated that %sum for isoinertial teamwork lifting did not change with team size. Sharp, Rice, Nindl, Mello, and Bills (1998) further provided a low-cost, gender-free prediction equation for teamwork lifting and carrying capability that could be used for preassignment screening of military or civilian personnel.

Marras, Davis, Kirking, and Granata (1999) and Dennis and Barrett (2002) conducted a biomechanical analysis for a two-person teamwork lifting task and found a significant reduction in L4/L5 torque and lumbar spinal compression force in teamwork lifting as compared with individual lifting. Although many studies have indicated that people exerted less strength or suffered less strain per individual under teamwork lifting as compared with one-person lifting, Johnson and Lewis (1989) found an increased psychophysically determined teamwork lifting capacity for two-person manual handling tasks using height-matched participants.

Hence, the literature associated with teamwork lifting seems to offer some interesting paradoxes. One possible reason for this might be the variability of participants. Most previous studies recruited inexperienced or height-unmatched participants who lacked teamwork coordination knowledge; hence the decreased human performance in teamwork is reasonable. The main objective of this study was to examine the additivity of isometric teamwork lifting strength for experienced and height-matched participants. The basic assumption of this study was that experienced and height-matched participants would enhance the additivity of teamwork lifting strength.

METHOD

Participants

Twelve healthy men from the same class in university volunteered to participate in this study. The participants were medically screened prior to their...

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