Frequency of stimulation and force (Recruitment of motor units and force)
• Muscle tension depends on the frequency of stimulation. • Muscle twitch: First stimulus. • Wave summation: When a second stimulus excites a partially relaxed muscle, producing a stronger contraction. • Unfused tetanus: Successive stimulations at the same frequency, producing a series of contractions with increasing tension. • Fused tetanus: Rapid stimulations without muscle relaxation, producing a smooth, sustained contraction. Recruitment of motor units and force • An increase in number of motor units involved in contraction increases contraction force of the muscle. • Threshold stimulus: Activates single motor unit to produce a very small force of contraction. • Submaximal stimulus: Activates multiple recruited motor units to produce a greater force of contraction. • Smaller and weaker motor units are recruited first. Larger and stronger motor units are added as needed. • Maximal stimulus: Activates all motor units to produce maximum contraction force. • A muscle under maximal stimulus can only contract for a short time. Recruitment (asynchronous) of motor units and force • Alternately contracting motor units allow the muscle to sustain contraction for longer periods of time. • This method of recruitment, known as asynchronous recruitment, allows the individual motor units time to recover from contraction. They recover by regenerating more ATP during their period of relaxation. Recruitment of motor units - muscle tone • Muscle tone is a firmness (partial contraction) sustained by small groups of alternately contracting motor units. These contractions are not strong enough to produce movement. • Muscle tone is important to maintain muscle health and in situations where muscles maintain position or pressure. • If neural damage occurs, then muscle tone will diminish and muscle cells will become flaccid.
You must login to add videos to your playlists.