Exercise‐induced muscle damage in healthy men with low choline intake
Authors: Kohlmeier Martin , Dong Olivia 
Published: November 2023

Both very low choline intake and intense exercise in healthy men can trigger peak muscle soreness a few days later and a rise of creatine kinase (CK) activity in peripheral blood indicating muscle damage.We wanted to know whether men susceptible to exercise‐induced muscle damage have lower dietary choline intake than men with more robust muscles and whether their heightened muscle fragility is associated with low lean body mass.We investigated in 58 healthy Caucasian men the increase of CK activity three days after 12 eccentric elbow flexors (Biodex 4, Biodex Medical Systems Inc., Shirley, NY) with the non‐dominant arm. This single bout of exercise took little more than one minute to complete. The dynamometer tracked the patient's torque and provided instant feedback throughout the exercises. The same measurements and exercises were done on the non‐dominant arm at the initial visit and three days later. Participants indicated on an analog scale after each exercise test the level of discomfort or pain they had experienced. A whole body dual energy x‐ray absorptiometry scan (Lunar iDXA, GE Healthcare) was used for the assessment of body composition and to estimate total and regional lean body masses. A trained dietitian supervised the automated 24‐hour diet recall assessments on days 1 and 4 for each subject with the ASA24 online system, demonstrated food models for improved accuracy of portion sizes, confirmed reported food items and probed for missing food items prior to submission, and asked additional quality control questions to promote comprehensive reporting. The recall on day 2 was reviewed and discussed with the participant over the phone.The study was registered at Clinicaltrials.gov (NCT01722448).The median change of CK activity three days after the initial bout of exercise was +49 U/L (+36%). We classified a significant minority (9 of 58) of the investigated men as high responders (HR) because they had exceptionally high CK activity after the exercise (between 4 and 27 times of the upper reference limit). At the other end of the spectrum were men (19 of 58) with no increase of CK activity (non‐responders, NR); their median change of CK activity was −22 U/L (−20%).The single bout of eccentric arm flexor exercise greatly reduced arm strength in HR when assessed three days later, but changed strength very little in NR. Average power in HR was 32% lower than initially (p<0.0005), while NR had an average decrease of 7%. The difference in response between the two groups was statistically highly significant (p<0.00001). Lean body mass was 10% lower in HR than in NR (17.1 vs. 19.1 kg/m2, p<0.04).More HR reported low choline intake (less than an average of 330 mg/day or 60% of adequate intake, AI) than NR (7 of 9 vs. 6 of 19, p<0.05). Men with higher choline intake also tended to have less muscle soreness (r = −0.261, p<0.05), better muscle performance after exercise (r = 0.310, p<0.02), and higher lean body mass (r = 0.383, p<0.005).These findings support our initial hypothesis that men susceptible to exercise‐induced muscle damage are more likely to have low choline intake than men with more resilient muscles. Increased vulnerability to intense exercise may discourage HR men to engage in physical activities and limit their ability to build up and maintain high muscle mass.Support or Funding InformationSupported by a grant from the UNC Nutrition Research Institute