title: Reliability of maximal muscle force and voluntary activation as markers of exercise-induced muscle damage.
abstract: The loss of the ability of skeletal muscle to generate force is one of the most appropriate and valid means to quantify muscle damage. Routine measurements of maximal muscle force, however, include many potential sources of error, the most important of which may be a possible lack of central drive to the muscles. The aim of the present study was to determine the reliability of maximal isometric quadriceps muscle force and voluntary activation over a time scale that is typically employed to examine the aetiology of exercise-induced muscle damage. We also attempted to characterise the reliability of several twitch interpolation variables including the size of the interpolated twitch and the state (i.e. un-potentiated vs potentiated) and size of the resting twitch. Over a 7-day period, eight healthy active males performed repeated maximal voluntary isometric contractions (MVC) of the quadriceps (baseline and 2 h, 6 h, 24 h, 48 h, 72 h and 7 days post). Systematic variations in maximal muscle force, voluntary activation, interpolated twitch, un-potentiated twitch and potentiated twitch were not statistically significant (P>0.05) and 95% repeatability coefficients of +/-76.03 N, +/-4.42%, +/- 8.44 N, +/-25.92 N and +/-43.58 N were observed, respectively. These data indicate that young healthy well-familiarized male subjects can reproduce their perceived maximal efforts both within and between days where activation levels of >90% are routinely achieved. Providing activation remains within these limits in the 7 days following an acute bout of exercise, the researcher would be 95% certain that exercise-induced muscle damage is present in individual subjects (taken from similar subject populations) if MVC force falls outside these limits.
authors.affiliation: Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, 15-21 Webster Street, Liverpool, L3 2ET, UK. SPSJMORT@livjm.ac.uk
authors.forename: James Peter
authors.initials: JP
authors.lastname: Morton
authors.forename: Greg
authors.initials: G
authors.lastname: Atkinson
authors.forename: Donald Pm
authors.initials: DP
authors.lastname: MacLaren
authors.forename: Nigel Tim
authors.initials: NT
authors.lastname: Cable
authors.forename: Gareth
authors.initials: G
authors.lastname: Gilbert
authors.forename: Caroline
authors.initials: C
authors.lastname: Broome
authors.forename: Anne
authors.initials: A
authors.lastname: McArdle
authors.forename: Barry
authors.initials: B
authors.lastname: Drust
mesh_terms: D000328:Adult; D012090:Cumulative Trauma Disorders / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*; D026241:Exercise Movement Techniques / Q000009:adverse effects; D005080:Exercise Test / Q000379:methods*; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000293:injuries* / Q000503:physiopathology*; D010807:Physical Endurance; D010808:Physical Examination / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D013314:Stress, Mechanical; D014836:Volition