Predictors Of Performance On A Mechanical Starter Replacement Task

Abstract

Job performance of Army Light-Wheel Vehicle Mechanics (MECHS) was studied due to their high rates of back pain/injury and injury hospitalization. Subject matter experts reported starter replacement (SR) is one of the most physically-demanding, frequently performed, and critical tasks. SR requires the MECH to bolt a 16 kg starter to the under side of a military vehicle. PURPOSE To determine relationships between MECHS characteristics (strength, experience, and self-rating of expected performance [SR rate]) and SR time. METHODS 135 male and 9 female MECHS (Mean±SD; age= 25.5±5.9 yrs, height=175.1±7.4 cm, weight= 80.0±13.4 kg), were timed during a standardized SR task. MECHS performed muscular strength tests (isometric: back extension [BE], elbow and leg extension and flexion [EE, EF, LE, LF], and dynamic: lift [DL] and bench press [BP]), and completed a job physical demands questionnaire. RESULTS Three females (33%) and 12 males (11%) were unable to finish the task within the 45 min cutoff. There were no significant differences between the pass/fail groups on any of the descriptive variables measured. The mean SR time was 16.3±8.2 min, (range=4.4 – 43.1 min). Univariate analysis showed that variables correlated (p<0.05) with SR time included measures of strength: EE (r=−0.35), LE (r= −0.27), DL (r= −0.26), BP (r= −0.20), LF (r=−0.23); experience: military rank (r= −0.33), time in job (r= −0.32); self-rating: SR rate (r= 0.32), and physical characteristics: weight (r= −0.28), and age (r=−0.25). Multiple regression revealed that 19% of the variance in SR time was accounted for by EE and military rank (SEE =7.3 min). CONCLUSIONS This indicates that subjective ratings of job performance, experience, and physical strength measures are related to performance of a physically-demanding, skilled MECHS task. While these relationships are not strong enough to use as selection criteria to identify superior MECHS, regression analyses revealed that muscle strength measures were related to SR time. This suggests MECHS should include progressive resistance exercise as part of their physical training. Reduced strength in MECHS may limit their ability to complete essential job tasks and may be related to injury potential.