Effect of straddle stance and dominance on limb loading asymmetries when lifting

Abstract

A straddle stance is often prescribed when lifting a box from the floor. The goal of this study was to assess the effects of stance on the lower limb load distribution when lifting a crate from the floor to standing hip height. Eighteen healthy young adult men (n = 9) and women (n = 9) with dominant right leg (i.e., preferred kicking leg) volunteered [age = 22.0 ± 1.0 yrs (mean ± SD), height = 171.2 ± 8.8 cm, body mass = 66.2 ± 10.0 kg]. After practice and warm up, five lifts (men = 17 kg, women = 12 kg) were performed in each of three separate stances: dominant foot forward (DFF), non-dominant foot forward (NDFF) and a symmetric (SYM). Limb loading was quantified as the percent of the average total vertical force under each foot from the start of the counter movement through completion of the limb extension after picking up the crate. Overall, limb loading asymmetries were greater when lifting with the DFF than SYM stance with neither different from the NDFF stance [main effect p = 0.011: DFF = 7.0 ± 6.3, NDFF = 4.8 ± 5.1, SYM = 2.5 ± 1.5 abs|D%−ND%|]. When examining the load distribution between the D and ND sides, all three lifting conditions were significantly different from each other [p < 0.001: DFF = −6.9 ± 6.4, NDFF = 2.1 ± 6.8, SYM = −1.3 ± 2.6 D%−ND%]. There was also a significant difference between DFF and NDFF asymmetries when compared as trail and lead leg [p = 0.011: DFF = 6.9 ± 6.4, NDFF = 2.1 ± 6.8 Trail%−Lead%]. However, after adjusting for the asymmetry present during SYM stance lifting, where subjects placed significantly more load on their ND foot [p = 0.038], the trail limb was preferentially loaded more than the lead limb in each of the straddle stance conditions with no difference between DFF and NDFF [p = 0.204: DFF = 5.5 ± 6.1, NDFF = 3.5 ± 6.8 Trail%−Lead%]. Repeat measures on eight subjects were consistent with initial visits (Chronbach's Alpha ≥ 0.789). When surveyed on which asymmetric lift they preferred, 67% chose the DFF stance. Based on these results, there is a tendency to place more weight on the trailing limb when lifting with a straddle stance. However, this is heavily mitigated in the NDFF stance. Relevance to industryWhile not preferred by most subjects, the NDFF straddle stance should be used in an attempt to minimize any potential limb loading differential. However, if the load is heavy, awkwardly shaped requiring a large straddle or multiple repetitions, it might be most appropriate to switch lead legs from lift to lift.