Individuals have unique muscle activation signatures as revealed during gait and pedaling.

Although it is known that the muscle activation patterns used to produce even simple movements can vary between individuals, these differences have not been considered to prove the existence of individual muscle activation strategies (signatures). We used a machine learning approach (support vector machine) to test the hypothesis that each individual has unique muscle activation signatures. Eighty participants performed a series of pedaling and gait tasks. 53 of these participants performed a second experimental session on a subsequent day. Myoelectrical activity was measured from 8 muscles: vastus lateralis and medialis, rectus femoris, gastrocnemius lateralis and medialis, soleus, tibialis anterior, biceps femoris-long head. The classification task involved separating data into training and testing sets. For the within-day classification, each pedaling/gait cycle was tested using the classifier, which had been trained on the remaining cycles. For the between-day classification, each cycle from day 2 was tested using the classifier, which had been trained on the cycles from day 1.When considering all 8 muscles, the activation profiles were assigned to the corresponding individuals with a classification rate of up to 99.28% (2353/2370 cycles) and 91.22%(2343/2370 cycles) for the within-day and between-day classification, respectively. When considering the within-day classification, a combination of 2 muscles was sufficient to obtain a classification rate >80% for both pedaling and gait. When considering between-day classification, a combination of 4-5 muscles was sufficient to obtain a classification rate >80% for pedaling and gait. These results demonstrate that strategies not only vary between individuals, but are unique to each individual.