Recumbent Cycling and Functional Electrical Stimulation for Lower Limb Rehabilitation

This study evaluates two different control strategies for a rehabilitation device that combines recumbent leg-cycling with functional electrical stimulation (FES) of the quadriceps muscle. The device assists pedaling using a motor and electrical stimulation, and is intended for use after knee surgery (such as ACL reconstruction) or in other lower-limb rehabilitation. During muscle stimulation, fatigue can develop, which reduces the force produced by the stimulated muscle. This study compares a standard control strategy with a new strategy that adjusts stimulation based on the muscle's fatigue level, measured in real time. Healthy adult volunteers will complete two sessions on a recumbent stationary bicycle, 2 to 7 days apart. Each session lasts about 60 minutes and includes periods of pedaling with electrical stimulation, as well as isometric wall squats to induce muscle fatigue. Muscle activity, pedal force, and pedal position will be recorded throughout. The goal is to determine which control strategy produces more mechanical work from the leg muscles and better tracks the desired pedaling pattern, especially as fatigue develops.

Inclusion Criteria: * Age between 18 and 60 years. * Body weight less than 120 kg. * No injuries or conditions affecting the osteoarticular or musculoskeletal system. * No strenuous physical exertion of the lower limb within the previous 24 hours. * Willingness and ability to understand the content and scope of the experiment and to comply with its instructions. * Signed informed consent. Exclusion Criteria: * Pregnancy. * History of chronic pain, neuromuscular disorders, or lower-limb surgical interventions without medical clearance. * Use of analgesics within 24 hours prior to participation. * Lack of cooperation. * Trauma to the segment under evaluation within the previous 4 weeks.