LAUSR

Intramuscular lipid (IMCL) utilisation during exercise was controversial as numerous studies did not observe a decline in IMCL content post-exercise was assessed in muscle biopsies using biochemical techniques. Contemporary techniques including immunofluorescence microscopy and 1H-magnetic resonance spectroscopy (1H-MRS) offer advantages over biochemical techniques. The primary aim of this systematic review, meta-analysis and meta-regression was to examine the net degradation of IMCL in response to an acute bout of cycling exercise in humans, as assessed with different analytical approaches. A secondary aim was to explore the factors influencing IMCL degradation including feeding status, exercise variables and participant characteristics. A total of 44 studies met the inclusion criteria using biochemical, immunofluorescence and 1H-MRS techniques. A meta-analysis was completed using a random effects model and percentage change in IMCL content calculated from the standardized mean difference. Cycling exercise resulted in a net degradation of IMCL regardless of technique (total effect -23.7%, 95% CI = -28.7 to -18.7%) and there was no difference when comparing fasted versus fed-state exercise (P > 0.05). IMCL degradation using immunofluorescence techniques detected larger effects in type I fibres compared to whole muscle using biochemical techniques (P = 0.003) and in type I fibres compared to type II fibres (P < 0.001). While IMTG degradation was associated with exercise duration, VO2 max, and BMI, none of these factors independently related to IMTG degradation. These findings provide strong evidence that the analytical approach can influence the assessment of IMCL degradation in human skeletal muscle in response to exercise.