Weakness of the hip girdle and upper thigh muscles, for instance in myopathies, leads to an instability of the pelvis on standing and walking. If the muscles extending the hip joint are affected, the posture in that joint becomes flexed and lumbar lordosis increases. The patients usually have difficulties standing up from a sitting position. Due to weakness in the gluteus medius muscle, the hip on the side of the swinging leg drops with each step (referred to as Trendelenburg sign). The gait appears waddling. The patients frequently attempt to counteract the dropping of the hip on the swinging side by bending the trunk towards the side which is in the stance phase (in the German language literature this is referred to as Duchenne sign). Similar gait patterns can be caused by orthopedic conditions when the origin and the insertion site of the gluteus medius muscle are closer to each other than normal, for instance due to a posttraumatic elevation of the trochanter or pseudarthrosis of the femoral neck.

Increased susceptibility to fatigue.

A type of Developmental delay characterized by a delay in acquiring motor skills.

Abnormally increased curvature (anterior concavity) of the lumbar or cervical spine.

The presence of an abnormal lateral curvature of the spine.

Sudden and involuntary contractions of one or more muscles.

A lack of strength of the proximal muscles.

Reduced strength of the musculature of the distal extremities.

The presence of skeletal muscular atrophy (which is also known as amyotrophy).

Muscle hypertrophy affecting the calf muscles.

Presence of abnormal vacuoles (membrane-bound organelles) in the sarcolemma. On histological staining with hematoxylin and eosin, rimmed vacuoles are popcorn-like clear vacuoles with a densely blue rim. The vacuoles are often associated with cytoplasmic and occasionally intranuclear eosinophilic inclusions.

Generalized muscular hypotonia (abnormally low muscle tone).

The presence of an abnormally increased amount of connective tissue.

An abnormal reduction on the vital capacity, which is defined as the total lung capacity (volume of air in the lungs at maximal inflation) less the residual volume (i.e., volume of air in the lungs following maximal exhalation) of the lung.