Related Experiment Video
Updated: May 25, 2026

Direct Linear Transformation for the Measurement of In-Situ Peripheral Nerve Strain During Stretching
Published on: January 12, 2024
The effects of active and passive stretching on muscle length
1Department of Cell Biology, Neurobiology & Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA. dariley@mcw.edu
Abstract:
Active stretch is necessary for regulating muscle fiber length (ie, the number of series sarcomeres). Elevated cytoplasmic calcium is the proposed component of contractile activity required to activate signaling pathways for sarcomere number regulation. Passive stretch reduces muscle tissue stiffness, most likely by signaling connective tissue remodeling via fibroblasts. Passive stretch may induce sarcomere addition if the muscle fibers are lengthened sufficiently to raise cytoplasmic calcium through stretch-activated calcium channels. The magnitude of stretch in vivo is limited by the physiologic range of movement and stretch pain tolerance. The greatest effect of stretching muscle fibers is expected when the lengthening exceeds the optimum fiber length (Lo).
Related Concept Videos
Relaxation of Skeletal Muscles
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.
Exercise and Muscle Performance
Endurance exercises
Endurance exercises involve running, swimming, or cycling, which require repetitive movements with low force output. When a person engages in endurance exercise, a few noticeable changes occur in their skeletal muscles. For instance, the number of capillaries...
Isotonic and Isometric Muscle Contractions
Isotonic contractions
Isotonic contractions occur when a muscle changes length while the...
Somatic Spinal Reflexes
One of the most well-known somatic spinal reflexes is the stretch reflex, which is activated by the sudden stretching of a muscle. This reflex involves the activation of specialized sensory receptors called muscle spindles, which are located in the muscle tissue and detect changes in the length and speed of muscle contractions. When a muscle is suddenly...
Muscle Stimulation Frequency
Wave summation
At low firing rates, motor neurons induce individual twitch contractions in muscle fibers. These twitches...
Peripherally and Centrally Acting Muscle Relaxants: A Comparison
Centrally acting muscle relaxants can be further divided into spasmolytic and antispasmodic drugs. Spasmolytic drugs,...

