The Direct Effects Of β-hydroxybutyrate On Skeletal Muscle Fatiguability And Recovery

Abstract

PURPOSE: Ketone bodies compose a group of energy substrates that may improve skeletal muscle performance, possibly by sparing glycogen and improving metabolic efficiency. This study aims to determine the direct effects of the ketone body β-hydroxybutyrate (3-OHB) on skeletal muscle fatiguability and recovery. METHODS: Rat soleus muscles were isolated and placed at 30 °C in one of four modified Krebs-Ringer solutions: No energy substrate, glucose (5 mM), Na-3-OHB (10 mM), or glucose (5 mM) + Na-3-OHB (10 mM). Muscles were electrically stimulated to contract and thereby fatigued for 90 minutes by a dynamic contraction protocol designed to mimic rodent locomotion. Peak force was measured during isometric twitch, doublet, non-fused tetanus (15 Hz), and tetanic (60 Hz) muscle activation. Assessments were performed before and after fatigue and during 90 min of recovery. Muscle glycogen content was determined at the end of the recovery period. RESULTS: Peak force declined to ~50% following the fatigue protocol with no significant differences between groups. After 90 min of recovery, muscles with no energy substrates available had regained tetanic force to 54% of the pre-fatigue value. The other groups recovered significantly more force: 3-OHB 61% (p = 0,016), glucose 62% (p = 0.004), and glucose +3-OHB 66% (p < 0,001). There were no major differences between different modes of activation. Compared with no energy substrate, the availability of glucose in the buffers resulted in 21% (p = 0.042) and 20% (p = 0.049) higher muscle glycogen concentrations for glucose only and glucose +3-OHB, respectively. Glycogen concentrations in muscles only exposed to 3-OHB were not significantly different from the glucose groups nor the no energy substrate group. CONCLUSION: 3-OHB aids initial force recovery when no other energy substrates are available to the muscle. However, compared to glucose, 3-OHB does not delay fatigue or improve recovery.