TY - JOUR

T1 - Effects of exercise training intensity and duration on skeletal muscle capillarization in healthy subjects: A meta-analysis

AU - Liu, Yujia

AU - Christensen, Peter Møller

AU - Hellsten, Ylva

AU - Gliemann, Lasse

N1 - Copyright © 2022 by the American College of Sports Medicine.

PY - 2022

Y1 - 2022

N2 - Purpose: This study aimed to investigate the effect of intensity and duration of continuous and interval exercise training on capillarization in skeletal muscle ofhealthy adults. Methods: PubMed and Web of Science were searched from inception to June 2021. Eligibility criteria for studies were endurance exercise training >2 wk in healthy adults, and the 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. Results: Fifty-seven trials from 38 studies were included (10%/90%, athletic/sedentary). C:F was measured in 391 subjects from 47 trials, whereas CD was measured in 428 subjects from 50 trials. Exercise training increased C:F (mean difference, 0.33 (95% confidence interval, 0.30–0.37)) with lowheterogeneity (I2 = 45.08%) and CD (mean difference, 49.8 (36.9–62.6) capillaries per millimeter squared) with moderate heterogeneity (I2 = 68.82%). Compared with low-intensity training (<50% of maximal oxygen consumption (VO˙2max)), 21% higher relative change in C:F was observed after continuous moderate-intensity training (50%–80% of VO˙2max) and 54% higher change after interval training with high intensity (80%–100% of VO˙2max) 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. Conclusions: In sedentary subjects, continuous moderate-intensity training and interval training with high intensity lead to increases in capillarization, whereaslow-intensity training has less effect. Within the time frame 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). 

AB - Purpose: This study aimed to investigate the effect of intensity and duration of continuous and interval exercise training on capillarization in skeletal muscle ofhealthy adults. Methods: PubMed and Web of Science were searched from inception to June 2021. Eligibility criteria for studies were endurance exercise training >2 wk in healthy adults, and the 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. Results: Fifty-seven trials from 38 studies were included (10%/90%, athletic/sedentary). C:F was measured in 391 subjects from 47 trials, whereas CD was measured in 428 subjects from 50 trials. Exercise training increased C:F (mean difference, 0.33 (95% confidence interval, 0.30–0.37)) with lowheterogeneity (I2 = 45.08%) and CD (mean difference, 49.8 (36.9–62.6) capillaries per millimeter squared) with moderate heterogeneity (I2 = 68.82%). Compared with low-intensity training (<50% of maximal oxygen consumption (VO˙2max)), 21% higher relative change in C:F was observed after continuous moderate-intensity training (50%–80% of VO˙2max) and 54% higher change after interval training with high intensity (80%–100% of VO˙2max) 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. Conclusions: In sedentary subjects, continuous moderate-intensity training and interval training with high intensity lead to increases in capillarization, whereaslow-intensity training has less effect. Within the time frame 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). 

KW - Faculty of Science

KW - Capillarization

KW - Exercise training

KW - Capillary to fiber ratio

KW - Capillary density

KW - Meta-analysis

U2 - 10.1249/MSS.0000000000002955

DO - 10.1249/MSS.0000000000002955

M3 - Review

C2 - 35522254

VL - 54

SP - 1714

EP - 1728

JO - Medicine and Science in Sports and Exercise

JF - Medicine and Science in Sports and Exercise

SN - 0195-9131

IS - 10

ER -