David is a 27-year-old male who is an active member of the Canadian military. As a way of simulating conditions encountered while on-field, he participated in a series of walking trials with Plantiga to evaluate how his gait pattern changes when carrying a backpack with varying loads. This case study highlights how Plantiga can help measure and quantify the effects of various loads on the body and its implication in evaluating fitness-for-duty.
David completed 7 walking trials with loads between 0kg and 31kg. Shown below are the changes in 5 relevant gait parameters as load was incrementally increased. Correlation lines are shown in green.
- Speed - David’s average walking speed decreased with a correlative value of -0.801. The decreased walking speed may be a result of fatigue from added weight, but it may also be a protective gait adaptation to avoid large rotations of the torso relative to the hips, as these larger rotations would produce more stress to the spinal column at higher loads.
- Stride Length - David’s stride length decreased with a correlation of -0.580. This is likely a gait strategy to lessen the joint strain to lower-body extremities by reducing the distance from the step to the body’s centre of mass. Additionally, the shorter stride length may reduce stress on the spine by avoiding large rotations of the torso relative to the pelvis.
- Cadence - David’s cadence decreased with a correlation of -0.776, which is to be expected from the slower walking speed and shorter stride lengths (Cadence = 2 * Speed / Stride Length).
- Double Support - David’s double support increased with a strong correlation of 0.997. As the load became heavier, David adapted to a more secure and stable gait pattern as noted by the greater percentage of time spent on both feet during a single gait cycle. This led to the decreased duration of load supported by only a single leg.
- Ground Contact Time (GCT) - David’s GCT increased with a correlation of 0.889. In considering the changes to the above parameters, this increase in GCT is unsurprising. Given the decrease in walking speed and increase, the time spent in the stance phase would be longer.
David’s gait pattern was heavily influenced by the changes in load carriage. To accommodate for the extra weight, David adapted to loading strategies that would help him bear the weight. His decreased walking speed, cadence, and stride length combined with increased double support and ground contact time demonstrate his attempt to properly distribute and support the added weight while avoiding excessive rotation of the torso relative to the pelvis.
As a practical application, monitoring the gait adaptations of a new recruit or someone returning from injury could shed light onto their physical fitness and readiness to bear the weight required for active duty. This insight could then lead to specific training regimens that could address deficiencies and ultimately reduce injury numbers.