Non-local muscle fatigue: effects and possible mechanisms.
BACKGROUND
Non-local muscle fatigue (NLMF) is characterized by muscle performance impairments in a contralateral or remote non-exercised muscle(s) following a fatiguing protocol of a different muscle group(s). This topic is of interest as it affords insights into physiological determinants of muscle fatigue and may provide practical applications concerning the order of exercises in training and rehabilitation programs.


METHODS
A literature review was conducted using Web of Science, PubMed, and Google Scholar databases to evaluate the NLMF effects and possible underlying mechanisms. Overall, 35 studies with 58 outcome measures that met the inclusion criteria were identified.


RESULTS
The literature is conflicting with approximately half of the studies reporting NLMF effects (32 of 58 measurements). However, on closer examination 76% of outcome measures of the lower limbs reported NLMF effects (23 of 30 measurements) compared to only 32% in the upper body (9 of 28 measurements). Thus, it appears that NLMF effects may be muscle group dependent. Also, tests that involve prolonged or repetitive contractions provide clearer evidence of NLMF. Other variables potentially influencing the size of the NLMF effect include the fatigued muscle groups, the protocols used to elicit the fatigue, gender and training background of participants.


CONCLUSIONS
While the NLMF literature is conflicting, certain variables appear to affect NLMF responses which can account for some of the discrepancies. Furthermore, the NLMF effects may be attributed to four different but interconnected pathways: neurological, biochemical, biomechanical and psychological.
School of Exercise and Health Sciences, Edith Cowan University, Perth, WA, Australia.|Physiology, Australian Institute of Sport, Canberra, Australia.
Israel
I
Halperin
School of Exercise and Health Sciences, Edith Cowan University, Perth, WA, Australia.|Physiology, Australian Institute of Sport, Canberra, Australia.
Dale W
DW
Chapman
School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, NL, A1C 5S7, Canada. dbehm@mun.ca.
David G
DG
Behm
D019054:Evoked Potentials, Motor; D006801:Humans; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D005082:Physical Exertion
Contralateral muscles; Cross-education; Crossover fatigue; Endurance; Force