Methods

A total of 4 male volunteers with a mean age of 23 ± 1 years, mean body height 180 ± 5cm and mean body weight 79 ± 5kg that had never been medically diagnosed with upper limbs injuries participated in this protocol. The protocol consisted of two-dimensional video recording of the upper limbs movement during a repetitive push-pull task. Three markers were placed on the right side of the volunteers' body, at the following points: 1) shoulder joint, 2) elbow joint and 3) wrist joint. The volunteers were asked to perform a bottling task by using two different bottling techniques (BTs). When using the 1^st technique the bottling machine was set on a 60cm workbench (pull technique). When using the 2^nd technique the bottling machine was set on the floor (push technique). The experiment was divided into three phases based on the perceptible fatigue (P.F.) of the volunteers (Borg's clinical rating scale) and each phase consisted of sixteen repetitions. During the experiment the pressure exerted by the volunteer's feet was measured by using a pelmatographer device. Changes of kinematics parameters were examined and compared to each other and to the participant's self-evaluated fatigue level.

Results

Our results showed that the mean wrist joint in relation to the shoulder joint velocity values, U (m/sec), were 45% higher when using the 2^nd BT compared to that when using the 1^st BT. Furthermore the Time to Substantial Fatigue Onset (TSFO) factor appeared 10% later when using the 2^nd BT compared to that when using the 1^st BT. The results obtained from the pelmatograms showed that the exerted feet pressure was 20% higher when using the 2^nd BT compared to that when using the 1^st BT.

Figure 1: Wrist joint in relation to the shoulder joint mean velocity values, U (m/sec). (a) 1^st bottling technique (b) 2^nd bottling technique.

Discussion

The results indicated that the 2^nd BT (push) was more appropriate compared to the 1^st BT (pull) concerning fatigue accumulation delay of the upper limbs probably due to better blood flow conditions. According to the researchers' findings, shoulder loading was highest when working above shoulder height [Holmstrom, 1992]. Furthermore the participants did not perceive the onset of fatigue early and continued their work despite the fact that fatigue accumulation had probably exceeded baseline level and became irreversible.

References

Holmstrom, Spine 17:672-677, 1992.
Ireland, Clinical orthopaedics and related research 63-73, 1998.
Kumar, S., Ergonomics 44:17-47, 2001.