The influence of physical exercise and sports on telomere length A model for telomere length and telomerase activity regulation based on a comparative assessment of literature

Based upon a comprehensive analysis of current literature and by combining a molecular biology and a sports science perspective, this review examines (1) if a correlation between physical activity load and telomere length (TL) exists, and (2) comprehensively analyses and integrates molecular pathways regulating exercise dependent TL dynamics. The focus is on TL in leukocytes and muscle tissue in middle to advanced aged subjects. Regarding item (1), a strong tendency for an increase in mean leukocyte TL was found for exercise energy expenditures up to about 2∙103 kcal/week, while for higher activity levels no conclusive statement can be made. Conversely, research on skeletal muscle TL so far is quite limited but suggests that physical exercise with prolonged eccentric muscle contractions rather acts to shorten telomeres, while sports with little eccentric contractions might rather act to lengthen telomeres. As to item (2), a model for hypothetical pathways for exercise dependent telomerase activity regulation is proposed by consolidating findings of different studies in different cells. Consistent with this pathway model, various studies report increased telomerase transcription or activation by exercise. Moreover, a qualitative overall model for endurance exercise related TL dynamics is presented. It considers telomeres as dynamic structures in equilibrium between telomere shortening (e.g., cellular turnover, oxidative stress, inflammation) and telomere lengthening (e.g., telomerase activity, telomerase recruitment) effects. A negative feedback-loop mediated by enhanced telomerase recruitment to short telomeres is assumed to counteract too excessive TL alterations. Finally, a proposal is put forth for future research on exercise dependent telomere dynamics by adopting a systems biology approach to develop mathematical models that properly integrate the complexity of the interacting variables.