Effects of Exercise Training Intensity and Duration on Skeletal Muscle Capillarization in Healthy Subjects: A Meta-analysis

• Published in: Medicine and science in sports and exercise
• Main Authors: Liu, Yujia, Christensen, Peter Møller, Hellsten, Ylva, Gliemann, Lasse
• Format: Journal Article
• Language: English
• Published: United States 01.10.2022
• ISSN: 1530-0315
• DOI: 10.1249/MSS.0000000000002955

To investigate the effect of intensity and duration of continuous and interval exercise training on capillarization in skeletal muscle of healthy adults. PubMed and Web of Science were searched from inception to June 2021. Eligibility criteria for studies were: endurance exercise training >2 wks in healthy adults, and capillary to fiber ratio (C:F) and/or capillary density (CD) reported. Meta-analyses were performed and subsequent subgroup analyses were conducted by the characteristics of participants and training scheme. 57 trials from 38 studies were included (10/90%, athletic/sedentary). C:F was measured in 391 subjects from 47 trials while CD was measured in 428 subjects from 50 trials. Exercise training increased C:F (Mean difference (MD) 0.33 [0.30-0.37; 95% CI]) with low heterogeneity (I2 = 45.08 %) and CD (MD 49.8 [36.9-62.6] Cap/mm2) with moderate heterogeneity (I2 = 68.82%). Compared to low intensity training (LOW, <50% of VO2max), 21% higher relative change in C:F ratio was observed after continuous moderate intensity training (CON, 50-80%VO2max) and 54% higher change after interval training with high intensity (INT, 80-100% of VO2max) in sedentary subjects. The magnitude of capillary growth was not dependent on training intervention duration. In already trained subjects, no additional increase in capillarization was observed with various types of training. In sedentary subjects, CON and INT leads to increases in capillarization, whereas LOW has less effect. Within the timeframe studied, no effect on capillarization was established regarding training duration in sedentary subjects. The meta-analysis highlights the need for further studies in athlete groups to discern if increased capillarization can be obtained, and if so, which combination is optimal (time vs intensity).