Selective Control Assessment of the Lower Extremities to probe the increased metabolic cost of walking after Stroke

Individuals post stroke show higher energy cost of walking compared to
able-bodied individuals. Although several factors such as an increase in
mechanical work, step length asymmetry and impaired balance control have been
associated to contribute to this increased energy cost, the underlying
mechanism remains unclear. The remaining impairments in motor control are
related to functional deficits of walking and might explain a part of the
increased energy cost of walking. These impairments manifest in an impaired
ability to independently control individual muscles due to neural constraints,
i.e. reduced selective control. Co-activation of the ankle plantar flexor
muscles with knee- and hip-extensor muscles reflects this reduced selective
control after stroke. Indeed, age-related adaptations in muscle co-activation
patterns have shown to be related to the increased energy cost of walking in
older adults. However, muscle co-activation could also serve as compensatory
strategy to increase stability during walking post-stroke, due to task
constraints of walking. To distinguish the neural constraints (reduced
selective control) from task constraints (co-activation as a stability strategy
in gait) after stroke, we will assess muscle co-activation during an isolated
leg swinging task and compared this to muscle co-activation during walking. We
hypothesise that there is a relationship between muscle co-activation during
isolated leg swinging and walking, which explains the increased energy cost of
walking in people post-stroke, but not in healthy adults.

The main objective is to examine the relationship between energy cost and (1)
hip extensor and knee extensor co-activation, (2) plantar flexor and hip
extensor co-activation and (3) plantar flexor and knee extensor co-activation
in able-bodied individuals and individuals post stroke during an isolated swing
movement of the leg.
The secondary objective is to examine the relationship between energy cost and
(1) hip extensor and knee extensor co-activation, (2) plantar flexors and
quadriceps co-activation and (3) plantar flexor and quadriceps co-activation
during walking.
The third objective is to examine whether the co-activation during the isolated
swing movement of the paretic leg explains increased energy cost during walking.
Both a younger (18-25 years) and older (50-75 years) able-bodied control group
will be assessed, to be able to distinguish between-group differences due to
age from between-group differences due to stroke.

This study is conducted as pilot study with a quasi-experimental study design.
Participants will perform three walking tasks on a treadmill and three leg
swinging tasks. Walking will be performed in three different speed conditions:
1) Comfortable walking speed (CWS), 2) Fixed walking speed (FWS; 0,6 m/s
normalized to leg length) and 3) increased walking speed (IWS = CWS x 1.3). The
three leg swinging tasks will be pace-matched to the leg-swinging frequency
during each respective walking condition. For safety, participants will wear a
safety harness attached to the ceiling to prevent them from falling during all
tasks.

In total, 36 participants are tested on one occasion which will take about
three hours. A very minimal risk of discomforts to participants is expected
from participation in the study.