Dynamic Contractility and Efficiency Impairments in Stretch-Shortening Cycle Are Stretch-Load-Dependent After Training-Induced Muscle Damage

<p>Vaczi, M, Racz, L, Hortobagyi, T, and Tihanyi, J. Dynamic contractility and efficiency impairments in stretch-shortening cycle are stretch-load-dependent after training-induced muscle damage. J Strength Cond Res 27(8): 2171-2179, 2013To determine the acute task and stretch-load dependency of neuromuscular impairments after muscle-damaging exercises, we examined the magnitude of strength deficits in isometric and stretch-shortening cycle (SSC) contractions after a single bout of exercise. Ten trained men performed 90 unilateral isokinetic eccentric-concentric knee extensions on a dynamometer. Plasma creatine kinase activity, muscle soreness, maximal isometric torque, short-range stiffness, and peak torque in the eccentric phase of the SSC contraction at 3 stretch-loads (120, 150, and 180 J) were determined in the quadriceps before and 24 hours after exercise. During SSC, positive mechanical work and efficiency were also calculated. Creatine kinase and soreness increased at 24 hours (p <0.05). In each of the 3 stretch-load conditions, muscle damage affected short-range stiffness less than isometric and peak SSC torque (p <0.05), providing evidence for a selective impairment in contractile function after muscle damage. With greater SSC stretch-load peak, SSC torque deficit increased linearly, whereas short-range stiffness deficit was unaffected. Efficiency declined only at the 180-J condition (p <0.05) as a result of decreased positive work (p <0.05). It was concluded that intense exercise produced microtrauma in the muscle, and a selective loss of force generating capacity, which suggests greater damage to the contractile machinery. Practitioners may expect greater acute impairment of force generation in movements that use large loads in their daily training drills. However, altered knee flexion strategy during SSC may compensate for the force deficit, preserving mechanical efficiency at smaller stretch-loads.</p>

Muscle fiber characteristics of competitive power lifters

To examine the skeletal muscle characteristics of power lifters, 5 competitive power lifters (PL; X̄ ± SE; age = 31.0 ± 1.5 years, squat = 287.7 ± 15.7 kg, bench press = 170.5 ± 17.7 kg, and deadlift = 284.2 ± 7.5 kg) and 5 untrained control subjects (CON; age = 27.3 ± 3.3 years) served as subjects. Isokinetic squat force and power was greater (p \u3c 0.05) for the PL at all bar velocities (0.20, 0.82, and 1.43 m · s-1), as was vertical jump height and estimated power. Muscle biopsies from the vastus lateralis m. revealed significant differences for percent fiber type (PL, IIA = 45.5 ± 1.6%, IIB = 1.3 ± 0.8%; CON, IIA = 33.4 ± 3.1%, IIB = 12.0 ± 2.4%); percent fiber type area (PL, IIA = 51.8 ± 1.6%, IIB = 1.3 ± 0.8%; CON, IIA = 43.5 ± 3.4%, IIB = 12.4 ± 2.6%); and percent myosin heavy chain isoform (PL, IIa = 59.5 ± 6.1%; CON, 46.5 ± 2.5%). Muscle fiber characteristics were significantly correlated (r = ± 0.61) with numerous strength and power measures for the PL. These data illustrate the muscle fiber characteristics necessary for the maximal force production requirements of power lifting

Muscle fiber characteristics of competitive power lifters

To examine the skeletal muscle characteristics of power lifters, 5 competitive power lifters (PL; X̄ ± SE; age = 31.0 ± 1.5 years, squat = 287.7 ± 15.7 kg, bench press = 170.5 ± 17.7 kg, and deadlift = 284.2 ± 7.5 kg) and 5 untrained control subjects (CON; age = 27.3 ± 3.3 years) served as subjects. Isokinetic squat force and power was greater (p \u3c 0.05) for the PL at all bar velocities (0.20, 0.82, and 1.43 m · s-1), as was vertical jump height and estimated power. Muscle biopsies from the vastus lateralis m. revealed significant differences for percent fiber type (PL, IIA = 45.5 ± 1.6%, IIB = 1.3 ± 0.8%; CON, IIA = 33.4 ± 3.1%, IIB = 12.0 ± 2.4%); percent fiber type area (PL, IIA = 51.8 ± 1.6%, IIB = 1.3 ± 0.8%; CON, IIA = 43.5 ± 3.4%, IIB = 12.4 ± 2.6%); and percent myosin heavy chain isoform (PL, IIa = 59.5 ± 6.1%; CON, 46.5 ± 2.5%). Muscle fiber characteristics were significantly correlated (r = ± 0.61) with numerous strength and power measures for the PL. These data illustrate the muscle fiber characteristics necessary for the maximal force production requirements of power lifting