The boy is suffering from Duchenne Muscular Dystrophy (DMD). This condition is a genetic disorder caused by a mutation resulting in absence of the dystrophin protein.

DMD is an X-linked recessive disease that caused muscle wasting and death. Mutations in the dystrophin gene on the X-chromosome cause absence of the protein dystrophin and instability in muscle cell membranes. Proximal muscles are affected first with noticeable atrophy of the legs and pelvis. This spreads to the arms, neck, and other parts of the body. Patients have pseudohypertrophy of the calves and deltoids and have poor endurance. Patients often show Gower’s sign, pushing on their thighs with their arms to help them stand up. A diagnosis is made with DNA testing or muscle biopsy showing absence of dystrophin. Becker’s muscular dystrophy is a less severe form of DMD in which mutated dystrophin is produced. Signs and symptoms are similar, but less severe.

Frataxin is a mitochondrial protein that is deficient in patients with Freidrich's ataxia, an autosomal recessive trinucleotide repeat disorder. It is the most common hereditary ataxia involving the posterior column, lateral corticospinal tracts, and spinocerebellar tracts of the spinal cord. This is a result of progressive atrophy and sclerosis of the dorsal root ganglia and dorsal roots. This condition is characterized by staggering gait, frequent falling, nystagmus, pes cavus, kyphoscoliosis, and hypertrophic cardiomyopathy.

Actin is a protein found in eukaryotes with multiple functions, including muscle contraction, vesicle and organelle transport, and cell signaling.

Troponin is a regulatory protein in muscle contraction. In skeletal muscle, troponin is bound to tropomyosin, a protein that covers actin binding sites, prohibiting muscle contraction. Binding of calcium to troponin causes a conformational change in troponin, which shifts tropomyosin to expose actin binding sites.

Huntingtin is a protein that, when mutated, causes Huntington's disease, a genetic disorder that progressively damages brain cells to result in chorea (jerky, uncontrollable movements) as well as changes in personality and dementia.

Golfer's elbow, or medial epicondylitis, is due to inflammation of the medial epicondyle of the elbow. The tendons of several muscles involved in flexing the forearm, wrist, and fingers originate at the medial epicondyle of the humerus at the elbow and this insertion point can become inflamed in response to injury.

Lateral epicondylitis is sometimes associated with tennis elbow.

When the nucleus propulsus inside an intervertebral disk protrudes through a weakened area of the annulus fibrosus, the ability of that disk to respond to torsion forces is severely compromised. Further, the protruding nucleus itself puts pressure on the vertebrae, resulting in a "compressed" or herniated disk. This can impact nearby nerves, resulting in radiating pain, weakness, and numbness or tingling.

Injury to the lateral thigh area could result in injury to the lateral cutaneous nerve of the thigh, which is associated with L2-L3.

L1 is associated with the ilio-inguinal nerve, located in the genital region. Both the obturator and femoral nerves are associated with L2-L4. 

The annular ligament of the radius stabilizes the radial head against the capitellum of the humerus. If this ligament is lax or damaged, the head of the radius can dislocate, leading to "nursemaid's elbow". This injury is most common in young children. The sternoclavicular and coracoclavicular ligaments do not articulate with the elbow, rather they are superior to the elbow, at the shoulder. The collateral ligaments of the elbow stabilize the joint but are not subject to the subluxation indicated in nursemaid's elbow.

The serratus anterior holds the scapula tight to the posterior wall of the chest. Damage to it, and especially to the thoracic nerve (descending from the axilla) causes this muscle to become paralyzed. Because of this, the scapula can project posteriorly from the back when actions such as pushing against a wall are performed.

The obturator nerve can be  damaged in car accidents, abdominal surgeries. It descends thru the pelvis to innervate the medial side of the thigh and adductor muscles of the thigh (external obturator, adductors longus, brevis, magnus and gracilis muscles). Adduction is movement of  an extremity closer to the midline of the body. Abduction is the reverse of adduction.

An indirect inguinal hernia is a congenital processes, where the bowel and peritoneum move through a patent processus vaginalis into the scrotum. In an indirect inguinal hernia the protrusion passes through the inguinal ring lateral to the inferior epigastric vessels. Males are significantly more likely than females to develop indirect inguinal hernias.

Direct inguinal hernias are loops of gut that enter through a weak point in the abdominal wall fascia. In direct inguinal hernias the defect is medial to the inferior epigastric vessels. Males are also significantly more likely to develop direct inguinal hernias. 

The peel-back mechanism refers to the torsional force that the long head of the biceps brachii places on the glenoid labrum, during shoulder abduction and end-range external rotation. This movement is common in baseball and other overhead sports. While the long head of the triceps brachii, the supraspinatus, and subscapularis are important for overhead shoulder stability, they do not contribute to the peel-back mechanism.

The lateral ligament of the ankle, which connects the fibula to the bones of the foot, is much weaker than the medial/deltoid ligament. For this reason, the lateral ligament is injured much more often in an ankle twist.