The contributions of ankle, knee and hip joint work to individual leg work change during uphill and downhill walking over a range of speeds

Abstract

The muscles surrounding the ankle, knee and hip joints provide 42, 16 and 42%, respectively, of the total leg positive power required to walk on level ground at various speeds. However, each joint's contribution to leg work when walking up/downhill at a range of speeds is not known. Determining each biological joint's contribution to leg work over a range of speeds and slopes can inform the design of biomimetic assistive devices (i.e. prostheses). Twenty healthy adults walked 1.00, 1.25 and 1.50 m s−1 on 0°, ±3°, ±6° and ±9° while we collected kinematic and kinetic data. We calculated sagittal plane joint work and individual leg work over the entire stance phase. The ratio of ankle joint to total individual leg positive work (summed ankle, knee and hip joint work) did not change (0.42) with speed or slope, but the ratio of ankle joint to individual leg negative work was 0.38 at −9°, 0.42 at 0° and 0.27 at +9° across all speeds. The ratio of ankle joint to total individual leg negative work was 0.41 at 1.00 m s−1 and 0.32 at 1.50 m s−1 across all slopes. The ratio of knee joint to total individual positive leg work (0.22) did not change with speed or slope. The ratio of knee joint to total individual leg negative work was 0.39 at 1.00 m s−1 and 0.45 at 1.50 m s−1 across all slopes. The ratio of hip joint to total individual leg positive work did not change with speed but was 0.34 at −9°, 0.33 at 0° and 0.37 at +9° across all speeds. The ratio of hip joint to total individual leg negative work was 0.21 at 1.00 m s−1, and 0.24 at 1.50 m s−1 across all slopes and 0.17 at −9°, 0.19 at 0° and 0.29 at +9° across all speeds. The ankle significantly contributes to walking on slopes and this contribution changes during sloped compared with level-ground walking, thus assistive devices that provide biomimetic ankle function must adapt to accommodate walking at different speeds and slopes; whereas assistive biomimetic devices for the knee only need to adapt at different speeds.

Modular footwear that partially offsets downhill or uphill grades minimizes the metabolic cost of human walking

“…We found that increases in treadmill grade from downhill (negative) to level or from level to uphill ( positive) also led to increasing dorsiflexion moments, positive ankle work rate, tibialis anterior and plantarflexor muscle activations. These results appear to be consistent with studies that found increased positive ankle work rate [58][59][60], tibialis anterior [10, 38] and plantarflexor muscle activations [7,8,10,38] during uphill walking. Additionally, we found that uphill walking decreased magnitudes of negative ankle work rate similar to other studies [58][59][60].…”

Muscle Eccentric Contractions Increase in Downhill and High-Grade Uphill Walking

“…Altered kinematics in sloped walking may also contribute to the variation of muscle eccentric contraction. For example, the range of motion of the hip in the sagittal plane is larger in uphill walking than in level walking (Lay et al, 2006;Montgomery and Grabowski, 2018), which was also observed in the current study (Supplementary Figure 1A). This increased range of motion led to a higher lengthening velocity of the hip flexors (e.g., iliacus) during hip extension in the stance phase of uphill walking, which caused increased negative power and consequently negative work in uphill walking, (Supplementary Figures 1B,D).…”

“…Our results suggested that the amount of negative work of lower limb muscles in sloped walking varied not only with the amount of the joint negative work but also with the muscle coactivations. Previous studies (DeVita et al, 2007;Alexander et al, 2017;Montgomery and Grabowski, 2018) and the current study ( Figure 3B) all showed FIGURE 6 | Mean hip (A; flexion is positive) and knee (B; flexion is positive) joint moments in one gait cycle (heel strike to heel strike) in downhill and level walking. Mean power (C), simulated activation (D) and measured activation (E) of rectus femoris (RF) in one gait cycle in downhill and level walking.…”

“…Our statistical analyses further corroborated that joint negative work was a significant predictor of the muscle negative work in sloped walking (Figure 5A). However, joint negative work, as typically calculated in previous studies (DeVita et al, 2007;Alexander et al, 2017;Montgomery and Grabowski, 2018), was only based on the net joint moments and joint angular velocities, which did not incorporate any potential influence from muscle coactivations. Muscle coactivations can lead to additional muscle negative work that is not reflected in net joint negative work.…”

“…In contrast, during downhill walking, the knee flexes more during the stance phase to lower the body down the slope (Lay et al, 2006;Dewolf et al, 2018). These differences lead to changes in the sagittal plane ranges of motion of all three lower limb joints (Lange et al, 1996;Kimel-Naor et al, 2017;Montgomery and Grabowski, 2018). In joint kinetics, sloped walking induces greater peak joint moments and joint compression forces in the hip, knee and ankle joints compared to level walking (Redfern and Dipasquale, 1997;Lay et al, 2006;Alexander and Schwameder, 2016c).…”