Sex, But Not Age, Associates With Whole Muscle Carnosine Content Of Trained Men And Women

Abstract

Carnosine is a dipeptide formed from the amino acids β-alanine and L-histidine, which contributes toward a number of essential processes in skeletal muscle metabolism. A number of modifiable (e.g., sex and age) and non-modifiable factors (e.g., training status) purportedly influence muscle carnosine content (MCarn), but little is known about the relative contribution of these factors. PURPOSE: To investigate the influence of modifiable and non-modifiable determinants of MCarn in a group of cycling-trained men and women. METHODS: 73 trained cyclists (54 men and 19 women, age 18 - 60) participated. Whole muscle MCarn was determined using high-performance liquid tomography, from a biopsy taken from m. vastus lateralis. All participants completed a self-report questionnaire of their current and previous training habits, and an exercise test battery (aerobic capacity testing, wingate test and a 4km time-trial). Body composition was assessed using the sum of 7 skinfolds. To describe relationships between MCarn and a range of demographic, performance and training-related factors, penalized regression in the form of LASSO (least absolute shrinkage and selection operator) analysis was completed. Models were generated using the glmnet package in R with associations described by regression coefficients and percentage inclusion in 10000 bootstrap samples. RESULTS: Sex (91% of models) and sum of skinfolds (69% of models), but not age (52% of models), training habits (13-30% of models), nor exercise test performance (4-45% of models), predicted MCarn. The LASSO model estimated women to have a median reduction of ~two units compared to men (-1.8, 95%CrI: -5.2 – 0)), while each 2SD increase in the sum of skinfolds resulted in an MCarn decrease of approximately 1 unit (-0.8; 95%CrI: -5.6 – 0). Repeating the model with men only identified no relevant associations (≤37% of models) on MCarn. CONCLUSION: Sex and body composition, but not age nor performance outcomes, had very small associations with whole muscle MCarn in a group of trained cyclists. These results imply that habitual training may reduce previously reported impacts of age on MCarn content (at least across the 4 decades investigated in this study). In contrast, women had lower MCarn content than men, even though their type and volume of training was similar.