Morphology and Anabolic Response of Skeletal Muscles Subjected to Eccentrically or Concentrically Biased Exercise

Abstract

Context Long-term eccentric exercise is known to promote muscle growth better than concentric exercise, but its acute effect on muscle is not well understood because of misinterpreted modeling and in situ and in vitro stretch protocols. Knowing if the initial bout of eccentric exercise promotes muscle growth and limits damage is critical to understanding the effect of this mode of exercise. Objective To directly evaluate the immediate effects of eccentric and concentric exercises on untrained muscle when fiber strains were physiological and exercise doses were comparable. Design Controlled laboratory study. Setting Laboratory. Patients or Other Participants A total of 40 skeletally mature male Long-Evans rats (age = 16 weeks, mass = 452.1 ± 35.2 g) were randomly assigned to an eccentric exercise (downhill walking, n = 16), concentric exercise (uphill walking, n = 16), or control (no exercise, n = 8) group. Intervention(s) Rats were exposed to a single 15-minute bout of eccentric or concentric exercise on a motorized treadmill and then were euthanized at 6 or 24 hours postexercise. We harvested the vastus lateralis muscle bilaterally. Main Outcome Measure(s) The percentage increase or decrease in protein abundance in exercised animals relative to that in unexercised control animals was evaluated as elevated phosphorylated p70S6k relative to total p70S6k. Fiber damage was quantified using immunoglobulin G permeability staining. One-way analysis of variance and post hoc Tukey tests were performed. Results Rats exposed to eccentric exercise and euthanized at 24 hours had higher percentage response protein synthesis rates than rats exposed to eccentric exercise and euthanized at 6 hours (P = .02) or to concentric exercise and euthanized at 6 (P = .03) or 24 (P = .03) hours. We assessed 9446 fibers for damage and found only 1 fiber was infiltrated (in the concentric exercise group euthanized at 6 hours). Furthermore, no between-groups differences in immunoglobulin G fluorescent intensity were detected (P = .94). Conclusions Incorporating eccentric exercise is a simple, universally available therapeutic intervention for promoting muscle recovery. A single 15-minute dose of eccentric exercise to a novice muscle can better exert an anabolic effect than a comparable dose of concentric exercise, with very limited evidence of fiber damage.

Eccentric Exercise as a Potent Prescription for Muscle Weakness After Joint Injury

“…Other key pathways that can be activated by stretch, such as the Akt/mammalian target of rapamycin (mTOR) pathway have also been reported to be upregulated after eccentric exercise (41). For instance, in our own work, a 20-fold increase in the ribosomal protein S6 kinase (an essential hypertrophic protein) (42) was found in the eccentrically exercised animals compared with the concentric after just a single 15-min dose (23).…”

“…To address some of these issues, we have tested the direct effect of an initial bout of eccentric exercise on muscle in an untrained animal model (23). The goal of this experiment was to determine if a single bout of eccentric exercise causes muscle damage under normal physiological conditions when the anatomy is not adjusted and the animal is simply walking at a clinically translational dose (i.e., 15 min of exercise in total, 5-min bouts, 2 min of rest between bouts).…”

Osteochondral Allograft Transplantation in Professional Athletes: Rehabilitation and Return to Play

“…Loading decreases as the joint goes into the flexed position, during which controlled eccentric flexion distributes the applied load and protects the articular cartilage and intra-articular structures. [58][59][60][61] Teaching this eccentric control and enhancing the eccentric quadriceps strength is imperative in these athletes to help them realize that increasing this strength can help them decrease abnormal joint pressures and subsequent knee pain with progressive activities. This eccentric training should be continued throughout the rehabilitation process following this phase, as it has been shown to improve plyometric activities as well.…”

“…A movement assessment for the athlete can help identify weaknesses in the kinetic chain, and aid in the development of a global plan to allow the athlete for a more efficient return to their sport. 58 Strength becomes a primary target during this phase. In previous phases, pain may have limited the athlete's ability to perform strength training exercises.…”