A Threshold and Continuum of Injury During Active Stretch of Rabbit Skeletal Muscle

Abstract

Previous studies of acute muscle injury with active stretch used cyclic stretching or stretching the muscle to complete muscle-tendon dissociation. This study tried to determine minimal force required for skeletal muscle injury with one active stretch to establish an injury "threshold." Tibialis anterior and extensor digitorum longus rabbit muscles were actively stretched at 10 cm/sec to 60%, 70%, 80%, or 90% of the force required to passively fail tibialis anterior and extensor digitorum longus muscles of the control (contralateral) limb. Maximal isometric contractile force, tensile properties, histology, and electromyography were measures of injury. Both muscles of the 60% group showed no abnormalities in maximal isometric contractile force, tensile properties, histology, or electromyographic activity; 70%, 80%, and 90% groups showed diminished maximal isometric contractile force, muscle fiber disruption, edema, hemorrhage, and decreased electromyographic maximal voltage amplitude. The 90% group also showed alterations in tensile properties at failure along with connective tissue damage. Injury site included fiber disruption both at the distal myotendinous junction and muscle belly, with injury noted initially at the distal myotendinous junction in the 70% group. Electromyographic studies showed maximal isometric contractile force and maximal voltage correlated well as indices of damage. This study shows that a threshold and continuum for active stretch-induced injury exist, with muscle fiber disruption occurring initially and connective tissue disruption occurring only with larger muscle displacements.

High specific torque is related to lengthening contraction-induced skeletal muscle injury

“…In accordance with this theory, the idea of a force threshold for the initiation of muscle injury has been proposed by others (17,43), and data indicate that contraction forces approaching 115-120% of those produced during maximal isometric contractions may provide sufficient tensile stress to exceed the yield strength of a muscle fiber (43,45). In the present study, peak eccentric torque during 100-Hz EMS was, on average, 123% of MVIC, whereas peak torque during 25-Hz EMS was only 73% of MVIC (data not shown).…”

Eccentric Muscle Contractions: Their Contribution to Injury, Prevention, Rehabilitation, and Sport

“…104,133 Athletes with a history of recurring hamstring and adductor muscle injuries have greater impairment of their eccentric strength (2-fold) as compared to concentric strength, suggesting that improvements in the former may minimize the risk of injury. 47,72 Others have suggested that eccentric resistance exercise may prevent injury to the muscletendon unit by improving the muscle's ability to absorb more energy before failing. 9,72,143,162 Increased stiffness in tendons, 29 greater force at failure, and an improved ability to absorb energy at the musculotendinous junction result following eccentric resistance training.…”

“…47,72 Others have suggested that eccentric resistance exercise may prevent injury to the muscletendon unit by improving the muscle's ability to absorb more energy before failing. 9,72,143,162 Increased stiffness in tendons, 29 greater force at failure, and an improved ability to absorb energy at the musculotendinous junction result following eccentric resistance training. 66,132 The exact mechanism of this adaptation is not defined.…”

Study of cervical muscle response and injury of driver during a frontal vehicle collision

“…The average peak muscle loads for the SCM, SPL, and TRP are 11(1) N, 25(1) N, and 25(1) N, respectively (see Table 1). These values are lower than the ultimate failure loads, which are amplified according to differences in physiological characteristics [18,20]. These are even lower than the maximal isometric forces estimated by the biomechanical model, 170N for the SCM, 68N for the SPL, and 81N for the TRP [19].…”

“…can even occur under 70% of the ultimate failure load [18]. Because stretch tests on the human body are restricted for ethical reasons, the ultimate failure load is calculated from animal testing.…”