Neuromuscular strategies for the transitions between level and hill surfaces during walking

Abstract

Despite continual fluctuations in walking surface properties, humans and animals smoothly transition between terrains in their natural surroundings. Walking transitions have the potential to influence dynamic balance in both the anterior-posterior and medial-lateral directions, thereby increasing fall risk and decreasing mobility. The goal of the current manuscript is to provide a review of the literature that pertains to the topic of surface slope transitions between level and hill surfaces, as well as report the recent findings of two experiments that focus on the neuromuscular strategies of surface slope transitions. Our results indicate that in anticipation of a change in surface slope, neuromuscular patterns during level walking prior to a hill are significantly different from the patterns during level walking without the future change in surface. Typically, the changes in muscle activity were due to co-contraction of opposing muscle groups and these changes correspond to modifications in head pitch. In addition, further experiments revealed that the neck proprioceptors may be an initial source of feedback for upcoming surface slope transitions. Together, these results illustrate that in order to safely traverse varying surfaces, transitions strides are functionally distinct from either level walking or hill walking independently.

Figure 1.

Illustration of level walking strides (grey feet) and non-level strides (black feet) for (a) level surface to an uphill surface (L-UP), (b) uphill surface only (UP), (c) level surface to a downhill surface (L-DN) and (d) downhill surface (DN) only. Shaded regions represent the hill surface and non-shaded regions represent the level surface. The foot placement locations represent actual changes in step length as well as step width at the heel and toe. Each small box is equal to a 3 × 3 cm square (modified from Gottschall et al. [30]).

Figure 2.

Muscle activity mean envelope of all 20 participants for the (a,e) lateral gastrocnemius (LG), (b,f) tibialis anterior (TA), (c,g) rectus femoris (RF) and (d,h) biceps femoris (BF) during level walking (L, solid lines), six steps before the slope (6-UP/DN, long dashed lines), four steps before the slope (4-UP/DN, medium dashed lines), transition onto the slope (L-UP/DN, short dashed lines), and the stride on the slope (UP/DN, dotted lines) for the (a–d) uphill and (e–h) downhill conditions.

Figure 3.

Mean head pitch angle of all 20 participants during level walking (L, solid lines), six steps before the slope (6-UP/DN, long dashed lines), four steps before the slope (4-UP/DN, medium dashed lines), transition onto the slope (L-UP/DN, short dashed lines), and the stride on the slope (UP/DN, dotted lines) for the (a) uphill and (b) downhill conditions.

Figure 4.

Typical electromyography (EMG) records from a representative (a) anterior semimembranosus (aSM) and (b) iliopsosas (ILIO) muscle. The area following the solid line and prior to the dashed line is swing (Sw), while the area following the dashed line is stance (St).

Figure 5.

Typical EMG records from a representative semitendinosus (ST) muscle (a) before and (b) after a labyrinthectomy. The area following the solid line and prior to the dashed line is swing (Sw), while the area following the dashed line is stance (St).

Figure 6.

Typical EMG records from a representative vastus lateralis (VL) muscle before and after a labyrinthectomy. The area following the solid line and prior to the dashed line is swing (Sw), while the area following the dashed line is stance (St).

Figure 7.

Typical EMG records from a representative BF muscle before and after a labyrinthectomy. The area following the solid line and prior to the dashed line is swing (Sw), while the area following the dashed line is stance (St).