Evaluating Mobility Performance Transfer With An Ankle Exoskeleton From Trained To Untrained Military Tasks

Lower-limb exoskeletons can enhance physical mobility by assisting with walking. However, users typically need to practice specific tasks to integrate exoskeleton assistance into their movement. To accelerate training and ensure proficient real-world performance, it is important to assess whether adaptations learned during pre-defined tasks transfer to untrained tasks and environments. PURPOSE: Evaluate the versatility of our exoskeleton training protocol in performing untrained, army-relevant tasks. METHODS: N = 13 males (22.7 ± 4.8 years, 78.3 ± 8.8 kg) completed two training sessions, walking with an ankle exoskeleton on floor, sand-gravel, and stair terrains, both with and without a rucksack. Untrained tasks included walking with a 60-lb simulated artillery shell on floor or sand-gravel (Artillery Floor, Artillery Sand), and walking on cobblestone terrain with or without a rucksack (Rucksack Cobblestone, Unload Cobblestone). Tasks were performed in combat boots before training (PRE) and with the exoskeleton after training (POST). RESULTS: Compared to PRE, subjects showed similar VO2 across all tasks, with a trend toward a 16% lower VO2 for Unload Cobblestone at POST (POST: 13.6 ± 2.7 ml/min/kg, PRE: 16.2 ± 6.0 ml/min/kg, p = 0.081). Walking speed remained consistent, but subjects sustained Artillery Sand longer at POST (POST: 5.8 ± 0.7 min, PRE: 5.2 ± 1.2 min; p = 0.056). The cost of transport (CoT) was similar across tasks, with a trend toward lower CoT for Artillery Floor at POST (POST: 0.383 ± 0.080 ml/m/kg, PRE: 0.419 ± 0.088 ml/m/min, p = 0.095). Heart rate was significantly lower for Artillery Sand (POST: 145.0 ± 24.2 bpm, PRE: 158.8 ± 11.1 bpm, p = 0.045) and Unload Cobblestone (POST: 113.1 ± 12.9 bpm, PRE: 122.4 ± 12.4 bpm, p = 0.046). RPE was significantly lower for Artillery Sand (POST: 14.8 ± 2.4, PRE: 15.8 ± 2.1, p = 0.048) and Rucksack Cobblestone (POST: 12.7 ± 2.8, PRE: 14.1 ± 1.8, p = 0.023). CONCLUSIONS: The results showed that the adaptation learned from pre-defined tasks did not lead to significant improvements in untrained tasks, indicating a lack of transfer effect. However, subjects reported lower perceived exertion for Artillery Sand and Rucksack Cobblestone post-training. These findings suggest that challenging, army-relevant task conditions will require specific training tailored to those tasks. Supported by: W911QY2020005