Induction and Assessment of Exertional Skeletal Muscle Damage in Humans

Summary

This article describes a safe and reliable method to induce and quantify exertional skeletal muscle damage in human subjects.

Abstract

Contraction-induced muscle damage via voluntary eccentric (lengthening) contractions offers an excellent model for studying muscle adaptation and recovery in humans. Herein we discuss the design of an eccentric exercise protocol to induce damage in the quadriceps muscles, marked by changes in strength, soreness, and plasma creatine kinase levels. This method is simple, ethical, and widely applicable since it is performed in human participants and eliminates the interspecies translation of the results. Subjects perform 300 maximal eccentric contractions of the knee extensor muscles at a speed of 120°/sec on an isokinetic dynamometer. The extent of the damage is measurable using relatively non-invasive isokinetic and isometric measures of strength loss, soreness, and plasma creatine kinase levels over several days following the exercise. Therefore, its application can be directed to specific populations in an attempt to identify mechanisms for muscle adaptation and regeneration.

Introduction

The overall goal of this procedure is to induce exertional damage to the quadriceps femoris muscles using voluntary lengthening (eccentric) contractions in human subjects.

Contraction-induced skeletal muscle damage is a common consequence of exercise that is marked by delayed onset muscle soreness¹, transient strength loss, and elevated muscle-specific enzymes in the blood². Exertional muscle damage is most pronounced following exercise to which the subject is unaccustomed, particularly when eccentric contractions are involved³. Exertional muscle damage is typically benign. Soreness subsides, and bo....

Protocol

The following procedures are in accordance with the standards of the Brigham Young University Institutional review board (IRB).

1. Prepare the Contraction Protocols

NOTE: The following protocol instructions are based on the Biodex Advantage software. Navigating the software and operating the dynamometer will be different if different systems are used.

1. Isokinetic Strength Test Protocol
   1. To make the isokinetic protocol, open dynamometer control software on the computer and select the "Protocol" tab and then select the "Record" tab on the toolbar on the top of the screen. Selec....

Results

Using the methods presented here, baseline soreness, serum creatine kinase activity, and strength (isometric and isokinetic) measurements were taken in 7 untrained young men. The following day, the subjects underwent the muscle damaging eccentric contraction protocol described above. To provide indices of muscle damage, follow up assessments of strength, soreness and serum creatine kinase activity were made. Strength was measured immediately after as well as 24, 48, 72, and 96 hr after ex.......

Discussion

Several steps are critical to obtaining the desired results of this protocol. First, subjects must be adequately familiarized to the contraction protocols, particularly the force measurements. Be sure that the subject understands exactly what they are expected to do and give them an opportunity to practice the strength tests prior to data collection. Subjects who are not adequately familiarized with these procedures may show a learning curve over the days following the damage induction. This can be a confounding variable.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Biodex Dynomometer	Biodex Medical Systems	850-000	Other models are available and should produce similar results
Creatine Kinase kit	Sigma-Aldrich	MAK116
Serum Vacutainers	BD Bioscience	367812
Winged safety push button blood collection set	BD Bioscience	367338
Cryogenic vials	Sigma-Aldrich	V5007	We use the 2 ml vials to store serum aliquots