Muscle Weakness

Clinicians separate weakness into two very different complaints. True weakness means measurably reduced power: struggling to rise from a chair without arms, difficulty lifting the arms overhead to wash hair, or a foot that catches on stairs. Perceived weakness, far more common, means effort feels harder without any loss of power, and it belongs to the fatigue differential — anaemia, depression, sleep disorder, deconditioning, thyroid disease. Once true weakness is established, the pattern localises the problem. Proximal weakness affecting shoulders and hips suggests myopathy: inflammatory myositis, statin-associated muscle disease, thyroid disease, Cushing's syndrome, severe vitamin D deficiency, or an inherited muscular dystrophy. Distal weakness suggests neuropathy. Fatigable weakness that worsens through the day, with drooping eyelids or double vision, suggests myasthenia gravis. Asymmetric weakness with upper motor neuron signs suggests central pathology. Rapidly ascending weakness over days is Guillain-Barré syndrome and is a medical emergency. Sarcopenia — age-related loss of muscle mass and function — is the most common cause of gradual functional weakness after 60, and it responds to resistance training combined with adequate protein rather than to supplements alone. Severe vitamin D deficiency causes a genuine proximal myopathy that reverses on repletion, but this applies to deficiency, not to topping up already-adequate levels. Creatine has consistent evidence for improving strength gains when paired with resistance training in older adults.

• •Difficulty rising from a chair without using the arms
• •Trouble lifting arms above the head
• •Foot catching or slapping when walking
• •Weakness that worsens later in the day
• •Muscle aches or cramps with the weakness
• •Visible loss of muscle bulk

• •Sarcopenia and deconditioning
• •Thyroid disease, both over- and underactive
• •Statin-associated muscle symptoms
• •Severe vitamin D deficiency
• •Inflammatory myopathy (polymyositis, dermatomyositis)
• •Corticosteroid-induced myopathy
• •Myasthenia gravis
• •Guillain-Barré syndrome
• •Electrolyte disturbance, especially low potassium or calcium
• •Chronic kidney or liver disease

Muscle fibre loss and reduced motor unit recruitment in sarcopenia; inflammatory destruction of muscle fibres in myositis; impaired excitation-contraction coupling in thyroid and electrolyte disorders; neuromuscular junction antibody blockade in myasthenia; and impaired mineralisation with type II fibre atrophy in severe vitamin D deficiency.