This single-arm pilot study will assess the preliminary effectiveness of an intensive motor skill intervention (HABIT-ILE) combined with functional strength training (FST) in children with SMA who are receiving disease-modifying therapies. Participants will attend a HABIT-ILE + FST summer camp for 6 hours per day over a 3-week period, totaling 90 hours of training.

Spinal Muscular Atrophy (SMA) is a severe neuromuscular disorder marked by the progressive degeneration of alpha motor neurons in the spinal cord and brainstem, resulting in proximal muscle atrophy and weakness. Based on age of onset and the motor function achieved, children were historically categorized into functional groups. However, recent advances leading to the development of disease-modifying therapies (DMTs) have transformed the management of SMA. Outcomes are now primarily determined by the timing of DMT initiation, with early treatment-ideally before symptom onset-showing significant efficacy in improving motor function and survival. Despite these therapeutic breakthroughs, rehabilitation remains a cornerstone of care for children with SMA. Current clinical guidelines emphasize physical activity, muscle strengthening, and stretching. However, few studies have rigorously evaluated these interventions, and even fewer have examined their combined effects with DMTs. This gap underscores the need for innovative, evidence-based rehabilitation strategies that can complement pharmacological treatments and further promote functional outcomes. Hand-Arm Bimanual Intensive Therapy Including Lower Extremities (HABIT-ILE) is an intervention that integrates bimanual coordination with postural control and gross motor training. Grounded in motor skill learning principles, HABIT-ILE delivers high-intensity, structured practice of progressively increased motor difficulty tasks and functional activities, emphasizing voluntary active movement. The approach has demonstrated efficacy in children aged 6 months to 18 years with cerebral palsy (CP), a non-progressive neurodevelopmental disorder caused by early brain injury. Although SMA and CP differ in pathophysiology, both conditions involve motor impairments that may respond to intensive, task-specific motor training. In individuals with SMA, central neuroplastic mechanisms may help compensate for peripheral motor deficits, while targeted motor training could optimize recruitment and efficiency of residual motor units in the muscle. Strength training, in particular, has demonstrated beneficial effects in individuals with SMA, suggesting that emphasizing skill training requiring increasing endurance and progressively increasing the weights of objects participants handled, may be especially advantageous. In this context, augmenting HABIT-ILE with a functional strength training (FST) component tailored to individual goals may further enhance motor outcomes in this population. The aims of this prospective single-group intervention trial are to determine the effects of HABIT-ILE+FST on motor function in children with SMA receiving DMTs, and to assess retention of gains at 6 months, and to evaluate the effects of HABIT-ILE+FST on muscle fatigability using both clinical assessments and surface electromyography (sEMG). Participants will complete 90 hours of HABIT-ILE + FST training over a 3-week period (6 hours/day). It is hypothesized that this intervention will be well tolerated by children, enhance the acquisition of new motor skills, and foster greater functional independence in daily activities.

Inclusion Criteria:

• Have a confirmed SMA diagnosis
• Be 5-17 years old
• Complete all pre- and post-intervention assessments
• Understand and speak English
• Follow instructions without major cognitive or behavioral issues
• Have received a stable disease-modifying therapy (DMT) dose for ≥6 months
• Be classified as a sitter or walker (SMA type 2 or 3) with supported standing ability (score ≥1 on Item 18 of the HFMSE) without KAFOs, AFOs, or external standing devices

Exclusion Criteria:

• Orthopedic surgery within the past year
• New pharmaceutical treatment during the study
• Concurrent participation in another clinical trial