Eccentric exercise in vivo: strain-induced muscle damage and adaptation in a stable system

Isokinetic eccentric resistance training prevents loss in mechanical muscle function after running

The aim of the study was to verify whether 8 weeks of resistance training employing maximal isokinetic eccentric (IERT) knee extensor actions would reduce the acute force loss observed after high-intensity treadmill running exercise. It was hypothesized that specific IERT would induce protective effects against muscle fatigue and ultrastructural damages, preventing or reducing the loss in mechanical muscle function after running. Subjects were tested before and after IERT protocol for maximal isometric, concentric and eccentric isokinetic knee extensor strength (60° and 180° s(-1)). In a second session, subjects performed treadmill running (~35 min) and the previously mentioned measurements were repeated immediately after running. Subsequently, subjects were randomized to training (n = 12) consisting of 24 sessions of maximal IERT knee extensors actions at 180° s(-1), or served as controls (n = 8). The effects of acute running-induced fatigue and training on isokinetic and isometric peak torque, and rate of force development (RFD) were investigated. Before IERT, running-induced eccentric torque loss at 180° s(-1) was -8 %, and RFD loss was -11 %. Longitudinal IERT led to reduced or absent acute running-induced losses in maximal IERT torque at 180° s(-1) (+2 %), being significantly reduced compared to before IERT (p < 0.05), however, RFD loss remained at -11 % (p > 0.05). In conclusion, IERT yields a reduced strength loss after high-intensity running workouts, which may suggest a protective effect against fatigue and/or morphological damages. However, IERT may not avoid reductions in explosive muscle actions. In turn, this may allow more intense training sessions to be performed, facilitating the adaptive response to running training.

Clinical and morphological changes following 2 rehabilitation programs for acute hamstring strain injuries: a randomized clinical trial

STUDY DESIGN

Randomized, double-blind, parallel-group clinical trial.

OBJECTIVES

To assess differences between a progressive agility and trunk stabilization rehabilitation program and a progressive running and eccentric strengthening rehabilitation program in recovery characteristics following an acute hamstring injury, as measured via physical examination and magnetic resonance imaging (MRI).

BACKGROUND

Determining the type of rehabilitation program that most effectively promotes muscle and functional recovery is essential to minimize reinjury risk and to optimize athlete performance.

METHODS

Individuals who sustained a recent hamstring strain injury were randomly assigned to 1 of 2 rehabilitation programs: (1) progressive agility and trunk stabilization or (2) progressive running and eccentric strengthening. MRI and physical examinations were conducted before and after completion of rehabilitation.

RESULTS

Thirty-one subjects were enrolled, 29 began rehabilitation, and 25 completed rehabilitation. There were few differences in clinical or morphological outcome measures between rehabilitation groups across time, and reinjury rates were low for both rehabilitation groups after return to sport (4 of 29 subjects had reinjuries). Greater craniocaudal length of injury, as measured on MRI before the start of rehabilitation, was positively correlated with longer return-to-sport time. At the time of return to sport, although all subjects showed a near-complete resolution of pain and return of muscle strength, no subject showed complete resolution of injury as assessed on MRI.

CONCLUSION

The 2 rehabilitation programs employed in this study yielded similar results with respect to hamstring muscle recovery and function at the time of return to sport. Evidence of continuing muscular healing is present after completion of rehabilitation, despite the appearance of normal physical strength and function on clinical examination.

LEVEL OF EVIDENCE

Therapy, level 1b-.

The disabled throwing shoulder: spectrum of pathology-10-year update

In the 10 years since the current concept series entitled "The Disabled Throwing Shoulder: Spectrum of Pathology" was conceived and written, many studies have been reported that add much more information to the understanding of the disabled throwing shoulder (DTS). The editors of Arthroscopy and the authors of the original series believed that an update to the original series would be beneficial to provide an organized overview of current knowledge that could update the thought process regarding this problem, provide better assessment and treatment guidelines, and guide further research. A dedicated meeting, including current published researchers and experienced clinicians in this subject, was organized by the Shoulder Center of Kentucky. The meeting was organized around 5 areas of the DTS that were highlighted in the original series and appear to be key in creating the DTS spectrum and to understanding and treating the DTS: (1) the role of the kinetic chain; (2) the role and clinical evaluation of the scapula; (3) the role of deficits in glenohumeral rotation, glenohumeral internal rotation deficit, and total range-of-motion deficit in the causation of labral injury and DTS; (4) the role of superior labral (SLAP) injuries and rotator cuff injuries; and (5) the composition and progression of rehabilitation protocols for functional restoration of the DTS. The meeting consisted of presentations within each area, followed by discussions, and resulted in summaries regarding what is known in each area, what is not known but thought to be important, and strategies to implement and enlarge the knowledge base.

Eccentric exercise and delayed onset muscle soreness of the quadriceps induce adjustments in agonist-antagonist activity, which are dependent on the motor task

This study investigates the effects of eccentric exercise and delayed onset muscle soreness (DOMS) of the quadriceps on agonist–antagonist activity during a range of motor tasks. Ten healthy volunteers (age, mean ± SD, 24.9 ± 3.2 years) performed maximum voluntary contractions (MVC) and explosive isometric contractions of the knee extensors followed by isometric contractions at 2.5, 5, 10, 15, 20, and 30% MVC at baseline, immediately after and 24 h after eccentric exercise of the quadriceps. During each task, force of the knee extensors and surface EMG of the vasti and hamstrings muscles were recorded concurrently. Rate of force development (RFD) was computed from the explosive isometric contraction, and the coefficient of variation of the force (CoV) signal was estimated from the submaximal contractions. Twenty-four hours after exercise, the subjects rated their perceived pain intensity as 4.1 ± 1.2 (score out of 10). The maximum RFD and MVC of the knee extensors was reduced immediately post- and 24 h after eccentric exercise compared to baseline (average across both time points: 19.1 ± 17.1% and 11.9 ± 9.8% lower, respectively, P < 0.05). The CoV for force during the submaximal contractions was greater immediately after eccentric exercise (up to 66% higher than baseline, P < 0.001) and remained higher 24 h post-exercise during the presence of DOMS (P < 0.01). For the explosive and MVC tasks, the EMG amplitude of the vasti muscles decreased immediately after exercise and was accompanied by increased antagonist EMG for the explosive contraction only. On the contrary, reduced force steadiness was accompanied by a general increase in EMG amplitude of the vasti muscles and was accompanied by increased antagonist activity, but only at higher force levels (>15% MVC). This study shows that eccentric exercise and subsequent DOMS of the quadriceps reduce the maximal force, rate of force development and force steadiness of the knee extensors, and is accompanied by different adjustments of agonist and antagonist muscle activities.