Does the Directive to Avoid Low Back Flexion Hinder Physical Performance? Examining Isometric Strength in Postures Adopted During Light Mass Lifting

Objective Observe how instruction to avoid rounding the low back while lifting a relatively light mass impacts isometric lifting strength. Background As opposed to manual materials handling training directives recommending whole-body techniques such as a squat lift, targeting specific body regions such as low back curvature, theoretically affords workers greater flexibility to organize the rest of the body to reduce musculoskeletal loading without reducing physical performance. However, providing these directives during sub-maximal tasks may not prompt prioritization of physical performance as individuals self-organize, eventually making the intervention ineffective. Methods Forty participants (50% female) lifted a crate with and without the instruction to avoid rounding the low back. Postures at the initiation of crate lifting were replicated to test isometric strength. Results At the group-level, instruction decreased low back flexion ( p < 0.0001) but did not change strength ( p = 0.862). However, high heterogeneity motivated examining individual responses. Thirty-seven participants (92.5% of the sample) exhibited greater than 40% of their flexion range-of-motion during baseline lifting, a threshold below which passive tissue strain is typically minimized. Yet, 22 participants (55%) were unsuccessful in reducing low back flexion below this threshold with instruction. Independent from these postural response groups, 23 maintained (57.5%), 8 increased (20%) and 9 decreased (22.5%) isometric strength. Conclusion On average, physical performance potential was maintained in response to a low back postural directive. However, personalized movement coaching is needed to ensure the desired response for all. Application Manual materials handling training should include personalized movement coaching that considers both musculoskeletal loading and performance.