Limping on split-belt treadmills implies opposite kinematic and dynamic lower limb asymmetries

Abstract

Walking on a split-belt treadmill (each of the two belts running at a different speed) has been proposed as an experimental paradigm to investigate the flexibility of the neural control of gait and as a form of therapeutic exercise. However, the scarcity of dynamic investigations challenges the validity of the available findings. The aim of the present study was to investigate the dynamic asymmetries of lower limbs of healthy adults during adaptation to gait on a split-belt treadmill. Ten healthy adults walked on a split-belt treadmill mounted on force sensors, with belts running either at the same speed ('tied' condition) or at different speeds ('split' condition, 0.4 vs. 0.8 or 0.8 vs. 1.2 m/s). The sagittal power and work provided by ankle, knee and hip joints, joint rotations, muscle lengthening, and surface electromyography were recorded simultaneously. Various tied/split walking sequences were requested. In the split condition a marked asymmetry between the parameters recorded from each of the two lower limbs, in particular from the ankle joint, was recorded. The work provided by the ankle (the main engine of body propulsion) was 4.8 and 2.2 times higher (in the 0.4 vs. 0.8, and 0.8 vs. 1.2 m/s conditions, respectively) compared with the slower side, and 1.2 and 1.1 times higher compared with the same speed in the tied condition. Compared with overground gait in hemiplegia, split gait entails an opposite spatial and dynamic asymmetry. The faster leg mimics the paretic limb temporally, but the unimpaired limb from the spatial and dynamic point of view. These differences challenge the proposed protocols of split gait as forms of therapeutic exercise.

Figures

Fig. 1

Spatiotemporal gait parameters. From top to bottom, the panels show the spatiotemporal gait parameters indicated by the labels (ss TIME: single-stance time, ds TIME: double-stance time, ts TIME: total stance time). Pairs of bars are provided for each combination of belt speeds, given on the abscissa. The bars show the grand-mean (SD) across six subsequent strides performed by 10 participants for each parameter. The gray and black bars refer to the nondominant and the dominant side, respectively, in tied conditions. The white and the dashed bars refer to the same sides, becoming the slower and the faster sides in split conditions. *Statistically significant pairwise comparisons between lower limb sides on a same gait condition. Statistically significant comparisons of faster/slower side ratios (linearized through log-odd transformation) in the split conditions with respect to the dominant/nondominant side ratios in the tied conditions (i.e. 0408 vs. 0404, 0606, and 0808; and 0812 vs. 0808, 1010, and 1212), and between the two split conditions (i.e. 0408 vs. 0812).

Fig. 2

Kinematic, dynamic, and surface electromyography (sEMG) changes in joint parameters (on the ordinate) as a function of normalized stride time (on the abscissa, absolute mean duration within brackets) during walking on the force treadmill with belts running at 0.4 and 0.8 m/s (0408 split condition, upper panel on the left), with both belts tied at 0.4 m/s (0404 tied condition, upper panel on the right), at 0.6 m/s (0606 tied condition, lower panel on the left), and at 0.8 m/s (0808 tied condition, lower panel on the right). In each panel, the labels above the uppermost panel indicate the joint (ankle, knee, and hip from left to right, respectively) and the muscle (within brackets) analyzed in each column. From top to bottom, the rows show the joint sagittal rotations, the changes in muscle length, the joint sagittal power and the sEMG signal. The curves show the grand-mean of data recorded from six subsequent strides performed by 10 healthy adults. The horizontal bottom bars show the single-stance (dashed or filled background) and the double-stance (white background) time. The ‘whiskers’ show the total stance time SD. The dashed lines and bar segments show the dominant (fast in split gait) lower limb; the continuous lines and the filled bar segments show the nondominant (slow in split gait) lower limb.

Fig. 3

Kinematic, dynamic, and sEMG changes during walking on the force treadmill with split belts running at 0.8 and 1.2 m/s (0812 split condition, upper panel on the left), with both belts tied at 1.0 m/s (1010 tied condition, lower panel on the left), and with both belts tied at 1.2 m/s (1212 tied condition, lower panel on the right). Other information as in Fig. 2.

Fig. 4

Ankle power in the sagittal plane (ordinate) as a function of both the standardized stride time (right abscissa) and the belt speed combinations (gait conditions, left abscissa). The dashed and the continuous lines show the dominant (DOM) and nondominant (NON-DOM) side, respectively, becoming the faster and the slower side in the split gait modality, respectively.

Fig. 5

Dynamic gait parameters. From top to bottom, the panels refer to the dynamic gait parameters of ankle, knee, and hip joints. The left and right columns show the peak positive power and positive work, respectively. Note the different graphic scaling for the ankle compared with both the knee and the hip. Other indications as in Fig. 1.