Electromyography of the thigh muscles during lifting tasks in kneeling and squatting postures

Abstract

Underground coal miners who work in low-seam mines frequently handle materials in kneeling or squatting postures. To assess quadriceps and hamstring muscle demands in these postures, nine participants performed lateral load transfers in kneeling and squatting postures, during which electromyographic (EMG) data were collected. EMG activity was obtained at five points throughout the transfer for three quadriceps muscles and two hamstring muscles from each thigh. ANOVA results indicated that EMG data for nine of 10 thigh muscles were affected by an interaction between posture and angular position of the load lifted (p < 0.001). Muscles of the right thigh were most active during the lifting portion of the task (lifting a block from the participant's right) and activity decreased as the block was transferred to the left. Left thigh muscles showed the opposite pattern. EMG activity for the majority of thigh muscles was affected by the size of the base of support provided by different postures, with lower EMG activity observed with a larger base of support and increased activity in postures where base of support was reduced (p < 0.05). Thigh EMG activity was lowest in postures with fully flexed knees, which may explain worker preference for this posture. However, such postures are also associated with increased risk of meniscal damage. STATEMENT OF RELEVANCE: Kneeling and squatting postures are sometimes used for manual lifting activities, but are associated with increased knee injury risk. This paper examines the EMG responses of knee extensors/flexors to lifting in these postures, discusses the impact of posture and kneepads on muscle recruitment and explores the implications for work in such postures.

Gendered division of labor in a Celtic community? A comparison of sex differences in entheseal changes and long bone shape and robusticity in the pre‐Roman population of Verona (Italy, third–first century BC)

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Age-Related Differences in Maintenance of Balance During Forward Reach to the Floor

“…When crouching down, ankle plantarflexors and dorsiflexors coactivate (33,35). Furthermore, knee extensor strength would be expected to play a significant role in the recovery to an upright stance after crouching or kneeling, given the significant activity seen in thigh muscles during the upward recovery phase (36).…”

Muscular activity of lower limb muscles associated with working on inclined surfaces

“…Previous studies indicate that EMG activity normalized to single angle maximum voluntary contraction (MVC) in the lower limbs for various ranges of ankle and knee motion have been found to provide similar results to angle-specific EMG normalization (Knudson and Johnston 1993, Burden et al . 2003, Gallagher et al . 2011).…”