Abstract
BackgroundMechanical loading during exercise has been shown to promote tissue remodeling. Safe and accessible exercise may be beneficial to populations at risk of diminished bone and joint health. We examined the effect of drop height and instruction on knee loading during a drop-landing task and proposed a task that makes use of drop heights that may be appropriate for rehabilitation purposes and functional in daily life to examine transient knee joint loads.MethodsTwenty males (22.0 ± 2.8 years) performed drop landings from 22 cm (low) and 44 cm (high) heights, each under three instructions: “land naturally” (natural), “softly” (soft), and “stiffly” (stiff). Knee compression force and external flexion moment were estimated using three-dimensional inverse dynamics and normalized to body mass.ResultsPeak knee compression force was larger (p < 0.001) for high (17.8 ± 0.63 N/kg) than low (14.8 ± 0.61 N/kg) heights. There was an increase (p < 0.001) in the knee compression force across soft (11.8 ± 0.40 N/kg), natural (17.0 ± 0.62 N/kg), and stiff (20.2 ± 0.67 N/kg) instructions. Peak knee flexion moment in high-natural (2.12 ± 0.08 Nm/kg) was larger (p < 0.001) than in high-soft (1.88 ± 0.08 Nm/kg), but lower than in high-stiff (2.23 ± 0.08 Nm/kg). No differences in peak knee flexion moment were observed across instructions for the low height.ConclusionsWe propose a drop-landing task that creates a scalable increase in knee compression loading. The absence of increased knee flexion moment with drop from the low height, compared to high, suggests that individuals could perform the task without incremental risk of knee injury. This task could be used in future studies to examine the effect of acute bouts of mechanical loading on bone and cartilage metabolism.
Highlights
Mechanical loading during exercise has been shown to promote tissue remodeling
The purpose of the current study was (1) to explore a drop-landing task that makes use of drop heights that may be more appropriate for rehabilitation purposes and are functional in daily life and (2) to examine transient knee joint loads during the drop-landing response to examine the effect of drop height and instruction cues on knee joint loads, with a focus to evaluating the potential for incremental injury risk during the task
The Analysis of the Trial/Condition Order Effect There was no significant effect of order for the peak knee compression force or the peak knee flexion moment
Summary
Mechanical loading during exercise has been shown to promote tissue remodeling. Safe and accessible exercise may be beneficial to populations at risk of diminished bone and joint health. Shortterm and acute responses of skeletal and articular cartilage metabolism to physical activity have been reported [12,13,14]; findings across studies are difficult to compare because the types of activities and research methodology are not standardized [14]. Animal models have been used to examine the effects of mechanical loading on bone and articular cartilage [15, 16]; a comparable and standardized model to assess the acute response of bone and cartilage turnover to various levels of mechanical loading has not yet been clearly defined in humans [17]. To improve clinical utility of exercise that may result in a net formation of bone and cartilage in humans, it is important to have a standardized approach that allows researchers to examine responses, to quantify doses of mechanical loads, and to determine if a dose-response exists [14]
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