The ability of a muscle to perform work. Muscle strength correlates with muscle mass: The greater the muscle mass, or volume of muscle fibers, the greater the strength of the muscle. Strength training, also called resistance training and weight training, helps to build muscle mass by stimulating the growth of new muscle fibers. Muscle strength is important for movement; muscle groups must be able to support the body as it moves through the range of positions involved in activities such as walking.
Regular physical activity such as occurs in daily living sitting, standing, walking, reaching helps maintain a muscle group’s strength. When the nature of that activity changes, so does its effectiveness in maintaining muscle strength. Common gait disturbances in Parkinson’s disease are reduced arm swing and leg stride. The muscle groups that move the arms and legs gradually get less exercise as swing and stride shorten, and they have less strength. Muscle mass is reduced because the body has no need to carry the metabolic needs of tissues it does not use. Unused muscle fibers flatten and shorten, and fat cells infiltrate the spaces around them.
Suggestions for improving mobility and stability such as “Make a conscious effort to engage in a full arm swing and lift the foot completely up from the walking surface during each step” also help to maintain muscle strength by making muscles work to the full range of motion for the action. For most people, walking is one of the most effective strengthening activities. Gentle resistance exercises, such as lifting one-pound weights, also help to strengthen muscle groups.