Effect of sloped walking on lower limb muscle forces
Introduction
Muscles have been shown to be the major contributors to the joint contact forces [1], [2], [3], while gravitational and centrifugal forces combined contribute less than 5% of the total contact force [1]. Estimation of individual muscle forces can provide insight on tissue loading, and may lead to a better understanding of the musculoskeletal demands and potential risks of musculoskeletal injuries [4]. Since direct measurement of muscle forces is generally not feasible, non-invasive methods based on musculoskeletal modelling should be considered [4]. Previous studies have confirmed that the use of musculoskeletal models estimating lower limb muscle and joint loads during walking can provide detailed information [5], [6].
Sloped walking is associated with kinematic changes to raise the limb for toe clearance and heel strike, to lift the body during ascending, and for a controlled descent [7]. Furthermore, increases in lower extremity joint loadings have been reported compared to level walking [7], [8]. Joint moments, however, do not account for changes in muscle activation that may occur during downhill and uphill walking when compared to level walking and thus may not reflect the real joint loadings [5], [7]. Analysing sloped walking with the use of a musculoskeletal model has revealed increased hip, tibiofemoral and patellofemoral compression forces and decreased ankle joint compression forces during downhill walking, while uphill walking increased all lower limb joint forces with increasing inclinations [9]. Furthermore, mean tibiofemoral compression forces were lower or equal during downhill walking compared to the same inclination during uphill walking, while mean patellofemoral joint compression forces were found to be higher. Therefore, the analysis of knee joint forces has provided more insight into the structure loading conditions than joint moment analysis [9].
Several studies have analyzed lower limb muscle forces during level walking in able-bodied participants [1], [10], [11] as well as patients [6], [11], [12], but muscle forces during sloped walking have been minimally analyzed to date [5], [13]. Haight et al. [5] found reduced gastrocnemius, quadriceps and gluteus maximus muscle forces during slow (0.75 m/s), 6° uphill walking compared to faster (1.50 m/s), level walking. Dorn et al. [13] performed predictive simulations on uphill walking at varied inclinations and observed muscle force patterns similar to level walking for smaller inclinations (5° and 10°). For the higher inclinations (15° and 20°), the peak forces developed by the hamstrings, vasti, and gluteus maximus increased, while iliopsoas, rectus femoris, and tibialis anterior did not change. Soleus and gastrocnemii muscle forces developed a double-peaked pattern for the higher inclines and the soleus peaks increased. The predictive simulations also revealed that joint kinematics and kinetics patterns at smaller inclinations were closer to level walking [13], which is not consistent with previous experiments [7]. Therefore, experimental analyses of muscle forces during uphill walking are necessary to evaluate the results of the predictive simulation. Furthermore, it appears that no study to date, has investigated the effect of downhill walking on lower limb muscle forces using a musculoskeletal model.
The purpose of this study was to analyze lower limb muscle forces spanning the hip, tibiofemoral, patellofemoral and ankle joint during sloped walking at various inclinations using a musculoskeletal model. It was hypothesized that sloped walking leads to altered lower limb muscle forces compared to level walking. Amongst others, downhill walking is expected to increase quadriceps and decrease gastrocnemii and hamstrings muscle forces while uphill walking would increase all of them in comparison to level walking.
Section snippets
Participants
Eighteen healthy male participants (age: 27.0 ± 4.7 y, height: 1.80 ± 0.05 m, mass: 74.5 ± 8.2 kg) were recruited. The study was approved by the institutional ethics board and written informed consent was signed by all participants.
Data collection
Participants walked at a pre-set speed of 1.1 m/s on a ramp (6 m × 1.5 m) at different inclination angles of 0°, ±6°, ±12° and ±18° [9]. All participants wore the same type of standard indoor sport shoes (Puma SE, Germany). Speed was controlled via a timing device (Brower Timing
Results
Participants had to walk at a pre-set speed of 1.1 m/s and the mean walking speed at all inclinations was 1.1 ± 0.01 m/s. The gait analysis revealed significant main effects of inclination (p < 0.05) on all mean lower limb muscle forces. In general the pairwise comparisons revealed that all lower limb muscle forces, except gluteus medius, were significantly altered (p ≤ 0.02) during sloped compared to level walking (Table 1). During downhill walking, muscle forces of gluteus maximus (d > 0.69),
Discussion
The hypothesis that sloped walking leads to altered lower limb muscle forces compared to level walking was accepted, since all lower limb muscle forces (except gluteus medius) were significantly altered (Table 1). Amongst others, downhill walking increased quadriceps (>140%) and decreased hamstrings (<22%) and gastrocnemii (<22%) muscle forces. Uphill walking increased mean quadriceps (>96%), hamstrings (>36%) and gastrocnemii (12%) muscle forces. Furthermore, joint-muscle-force waveforms (Fig.
Conflict of interest
None of the authors had financial or personal conflict of interest with regard to this study.
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