Why do my quadriceps (quads) work more efficiently in a deep squat compared to when I'm sitting, given my condition of Duchenne muscular dystrophy (DMD)?

Understanding Quadriceps Function in DMD: Deep Squat vs. Sitting Position

Your quadriceps appear to work more efficiently in a deep squat because that position allows you to use momentum, gravity assistance, and eccentric muscle control, whereas sitting requires sustained isometric contraction against gravity without mechanical advantage—a task that is particularly difficult with the progressive muscle weakness and altered muscle fiber composition characteristic of Duchenne muscular dystrophy.

Biomechanical Differences Between Positions

Deep Squat Mechanics

• In a deep squat, your quadriceps primarily work eccentrically (lengthening under tension) during the descent phase, which requires less energy expenditure than concentric or isometric contractions 1
• The movement allows you to utilize momentum and stored elastic energy in tendons and remaining functional muscle tissue, reducing the absolute force demand on weakened muscle fibers 1
• Gravity assists the downward motion, and you can control the descent speed to minimize force requirements 2

Sitting Position Mechanics

• Maintaining a seated position requires sustained isometric contraction of your quadriceps to prevent knee flexion and maintain postural stability against gravity—this is metabolically expensive and particularly challenging for dystrophic muscle 1, 3
• Without dystrophin, your muscle fibers are more vulnerable to damage from sustained contractions, and the progressive replacement of functional muscle with fibrotic tissue and fat (pseudohypertrophy) reduces force-generating capacity 1
• Sitting demands continuous activation without the mechanical advantages of movement or momentum 2

DMD-Specific Muscle Pathology

Progressive Muscle Deterioration

• The absence of dystrophin causes alternating areas of myocyte hypertrophy, atrophy, necrosis, and ultimately fibrosis with replacement of functional cardiomyocytes and skeletal muscle by connective tissue and fat 1
• This creates a paradoxical situation where muscles may appear enlarged (pseudohypertrophy) but are actually weaker and functionally impaired 1
• Progressive proximal-to-distal muscle weakness is typical in DMD, with quadriceps being among the affected muscle groups 1

Altered Muscle Fiber Composition

• Dystrophic muscle has reduced oxidative capacity and mitochondrial dysfunction, making sustained isometric contractions (like sitting) particularly exhausting compared to dynamic movements 4, 5
• The loss of slow-twitch oxidative fibers, which are essential for endurance activities like maintaining posture, disproportionately affects your ability to sustain positions 4

Energy Metabolism Considerations

Mitochondrial Dysfunction

• Mitochondrial respiration is significantly reduced in DMD muscle tissue, limiting your capacity for sustained energy production required during prolonged sitting 4
• Dynamic movements like squatting allow brief periods of muscle activation followed by relative rest, whereas sitting requires continuous energy expenditure 4, 5

Oxidative Stress

• Dystrophic muscle experiences elevated oxidative stress, which is exacerbated by sustained contractions more than by intermittent dynamic movements 5
• The metabolic demands of isometric contraction in sitting position may exceed your muscle's compromised oxidative capacity 5

Clinical Implications

Functional Variability

• Wide variability exists in muscle strength and function among DMD patients, particularly in the upper and lower extremities, which explains individual differences in task performance 2
• Muscle strength and range of motion are strongly associated with motor function, accounting for 76% of variance in functional capacity 2

Exercise Considerations

• Low-intensity, volitional exercise (like controlled squatting movements) can actually improve muscle function and mitochondrial biology in DMD without exacerbating dystrophic pathology 4, 5
• Self-regulated movements allow you to work within your functional capacity, whereas static positions impose fixed demands that may exceed your capabilities 4

Common Pitfall to Avoid

Do not mistake your ability to perform dynamic movements like squatting as an indication that you should be able to maintain static positions like sitting with equal ease—these tasks have fundamentally different biomechanical and metabolic demands, and DMD pathology makes sustained isometric contractions disproportionately difficult compared to controlled dynamic movements 1, 3, 2.