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

Abstract

PurposeThis study aimed to investigate the effect of intensity and duration of continuous and interval exercise training on capillarization in skeletal muscle of healthy adults.MethodsPubMed 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.ResultsFifty-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 low heterogeneity (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 (V̇O2max)), 21% higher relative change in C:F was observed after continuous moderate-intensity training (50%–80% of V̇O2max) and 54% higher change after interval training with high intensity (80%–100% of V̇O2max) 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.ConclusionsIn sedentary subjects, continuous moderate-intensity training and interval training with high intensity lead to increases in capillarization, whereas low-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).

The impact of aging and physical training on angiogenesis in the musculoskeletal system

“…Furthermore, in the study by Zoladz et al (2005) , it was shown that the capillarisation of the quadricep muscles of sprinters was not higher than in endurance trained athletes ( Table 6 ). Therefore, the above-mentioned studies ( Torok et al, 1995 ; Zoladz et al, 2005 ) do not support the conclusion offered by the meta-analysis by Liu et al (2022) , that high-intensity interval training is indeed more effective in augmenting muscle capillarisation than continuous endurance training. Hence, the issue of the impact of low/moderate vs high-intensity exercise training on capillary density in case of long-lasting training (years) needs to be explored with further studies.…”

“…The summary of the effects of exercise training on skeletal muscle capillarisation in healthy subjects has been recently presented in a meta-analysis by Liu et al (2022) . Based on 57 trials from 38 studies, they demonstrated that there was a 21% higher relative change in the muscle capillary-to-fibre ratio after continuous moderate-intensity training (50–80% of VO 2max ) and 54% increase in this parameter after high-intensity interval training (80–100% of VO 2max ), whereas low-intensity training (<50% of VO 2max ) was less effective ( Liu et al, 2022 ).…”

“…The summary of the effects of exercise training on skeletal muscle capillarisation in healthy subjects has been recently presented in a meta-analysis by Liu et al (2022) . Based on 57 trials from 38 studies, they demonstrated that there was a 21% higher relative change in the muscle capillary-to-fibre ratio after continuous moderate-intensity training (50–80% of VO 2max ) and 54% increase in this parameter after high-intensity interval training (80–100% of VO 2max ), whereas low-intensity training (<50% of VO 2max ) was less effective ( Liu et al, 2022 ). However, these intriguing observations regarding the capillarisation responses to physical training concern a rather limited period of training (up to 48 weeks for endurance training, and up to a maximum of 8 weeks of interval training), during which more intense training (mainly interval) seems to be more effective than continuous endurance training in terms of its impact on muscle capillarisation.…”

The time is now: regular exercise maintains vascular health in ageing women

“…However, the influence of sex and ageing are less clearly understood. Studies investigating the impact of female hormones and menopause on skeletal muscle capillarization are rare, yet a recent meta-analysis showed clear sex-related differences in the capillary-to-fibre (C:F) ratio after a period of exercise training, whereby the increase in C:F ratio was 56% higher on average in males compared to females (Liu et al 2022). Currently, the findings from studies on training-induced muscle capillary growth in postmenopausal women are inconsistent (Gavin et al 2014;Gliemann et al 2021;Gries et al 2018;Olsen et al 2020;Perez-Gomez et al 2021).…”

A 6-day high-intensity interval microcycle improves indicators of endurance performance in elite cross-country skiers

“…However, in that study and the literature in general, there is lacking measurements of V̇O 2 during the HIT sessions in a microcycle. There seems to be growing evidence for the importance of accumulated time ≥90% of V̇O 2max to maximally stress cardiorespiratory parameters in well-trained endurance athletes ( 20 – 22 ), which also is an intensity domain known to induce a large muscular stimulus eventually leading to favourable muscular adaptations such as capillarization and improvements in mitochondrial functions ( 23 , 24 ). However, there is a lack of knowledge on the reliability of accumulated time ≥90% of V̇O 2max between interval sessions, thus making it difficult to know whether the result for a training session tested in the laboratory will be similar for the next training sessions, or when the session will be repeated outside the laboratory during more practical everyday training.…”