Tonus, also referred to as muscle tone, is a term used in physiology and medicine to describe the normal level of tension or resistance in resting muscles. It is a measure of the inherent tension present in muscles when they are at rest but still capable of contracting. Tonus is the result of the balance between the muscles' own contractile properties and the external forces acting on them.
Muscle tone is an essential characteristic that allows muscles to maintain proper posture, stability, and readiness for movement. It is attributed to the continuous and involuntary contractions of small groups of muscle fibers within larger muscle groups. These contractions provide a baseline level of activation that ensures prompt response and control during voluntary movements.
Tonus can be influenced by various factors, including genetics, physical activity, age, and neurological conditions. Abnormal tonus can manifest as either hypertonia (increased muscle tone) or hypotonia (reduced muscle tone). Hypertonia may lead to stiffness, rigidity, and difficulty in movement, while hypotonia may result in muscle weakness and decreased control.
Evaluating muscle tone is an important part of physical examinations and clinical assessments conducted by healthcare professionals. Techniques used to assess tonus include observation, palpation, and testing the resistance of muscles to passive movement. Understanding and monitoring tonus is crucial in diagnosing and managing conditions such as cerebral palsy, stroke, spinal cord injuries, and various neuromuscular disorders.
