An investigation of biomechanical signals and their contribution to joint action during team lifting

Abstract

Team lifting is required in many workplaces, particularly where heavy and awkward lifts are prevalent. Despite the known risk factors associated with team lifting, it remains under researched, with almost no 4-person lifting studies. The purpose of this thesis was to investigate how members of a 4-person team coordinate their actions during a lifting task that involved an unexpected release from a single team member. It involved a novel approach to investigating the mechanisms associated with joint action and whether these mechanisms may alert the remaining lifters that a release is imminent, where the goal was to elicit an unexpected response from the group. Data collected for a previous team lifting study was used. Six groups of four male participants (n = 24) performed 30 lifts with a constructed 60 kg lifting apparatus designed to transition between a rectangular (2 x 4 ft or 61 x 122 cm) and a square (2 x 2 ft or 61 x 61 cm) configuration. A total of 8 trials (4 per configuration) were designated as “drop trials”. Vertical force at the hands and right-side electromyography (EMG) of the biceps brachii (BB), anterior deltoid (AD), upper trapezius (UT), and the lumbar erector spinae (LES) was collected for each participant. Means and standard deviation of vertical force was compared from the pre-drop phase for both drop and non-drop (lift) trials. No significant differences were found between drop and non-drop trials during the pre-drop phase. A comparison of time to peak force and time to peak muscle activity was performed for lifters adjacent to the release position. These times were compared against a 25 to 150 ms window to determine whether the muscle activity was considered reflexive or anticipatory to the dropped load. A small proportion of the peak muscle activity values were considered anticipatory (6 BB and 2 LES), suggesting that while it is possible for the dropper to disguise the release, perhaps joint action provides insight to the other lifters. The complex mechanisms that support joint action, their connection to biomechanics and their role in team lifting warrants further research in order to determine how large of a role they might play.