Mølmen Knut Sindre, Almquist Nicki Winfield, Skattebo Øyvind
Section for Health and Exercise Physiology, Inland Norway University of Applied Sciences, P.O. Box. 422, 2604, Lillehammer, Norway.
The August Krogh Section for Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
Sports Med. 2025 Jan;55(1):115-144. doi: 10.1007/s40279-024-02120-2. Epub 2024 Oct 10.
Skeletal muscle mitochondria and capillaries are crucial for aerobic fitness, and suppressed levels are associated with chronic and age-related diseases. Currently, evidence-based exercise training recommendations to enhance these characteristics are limited. It is essential to explore how factors, such as fitness level, age, sex, and disease affect mitochondrial and capillary adaptations to different exercise stimuli.
The main aim of this study was to compare the effects of low- or moderate intensity continuous endurance training (ET), high-intensity interval or continuous training (HIT), and sprint interval training (SIT) on changes in skeletal muscle mitochondrial content and capillarization. Secondarily, the effects on maximal oxygen consumption (VOmax), muscle fiber cross-sectional area, and fiber type proportion were investigated.
A systematic literature search was conducted in PubMed, Web of Science, and SPORTDiscus databases, with no data restrictions, up to 2 February 2022. Exercise training intervention studies of ET, HIT, and SIT were included if they had baseline and follow-up measures of at least one marker of mitochondrial content or capillarization. In total, data from 5973 participants in 353 and 131 research articles were included for the mitochondrial and capillary quantitative synthesis of this review, respectively. Additionally, measures of VOmax, muscle fiber cross-sectional area, and fiber type proportion were extracted from these studies.
After adjusting for relevant covariates, such as training frequency, number of intervention weeks, and initial fitness level, percentage increases in mitochondrial content in response to exercise training increased to a similar extent with ET (23 ± 5%), HIT (27 ± 5%), and SIT (27 ± 7%) (P > 0.138), and were not influenced by age, sex, menopause, disease, or the amount of muscle mass engaged. Higher training frequencies (6 > 4 > 2 sessions/week) were associated with larger increases in mitochondrial content. Per total hour of exercise, SIT was ~ 2.3 times more efficient in increasing mitochondrial content than HIT and ~ 3.9 times more efficient than ET, while HIT was ~ 1.7 times more efficient than ET. Capillaries per fiber increased similarly with ET (15 ± 3%), HIT (13 ± 4%) and SIT (10 ± 11%) (P = 0.556) after adjustments for number of intervention weeks and initial fitness level. Capillaries per mm only increased after ET (13 ± 3%) and HIT (7 ± 4%), with increases being larger after ET compared with HIT and SIT (P < 0.05). This difference coincided with increases in fiber cross-sectional area after ET (6.5 ± 3.5%), HIT (8.9 ± 4.9%), and SIT (11.9 ± 15.1%). Gains in capillarization occurred primarily in the early stages of training (< 4 weeks) and were only observed in untrained to moderately trained participants. The proportion of type I muscle fibers remained unaltered by exercise training (P > 0.116), but ET and SIT exhibited opposing effects (P = 0.041). VOmax increased similarly with ET, HIT, and SIT, although HIT showed a tendency for greater improvement compared with both ET and SIT (P = 0.082), while SIT displayed the largest increase per hour of exercise. Higher training frequencies (6 > 4 > 2 sessions/week) were associated with larger increases in VOmax. Women displayed greater percentage gains in VOmax compared with men (P = 0.008). Generally, lower initial fitness levels were associated with greater percentage improvements in mitochondrial content, capillarization, and VOmax. SIT was particularly effective in improving mitochondrial content and VOmax in the early stages of training, while ET and HIT showed slower but steady improvements over a greater number of training weeks.
The magnitude of change in mitochondrial content, capillarization, and VOmax to exercise training is largely determined by the initial fitness level, with greater changes observed in individuals with lower initial fitness. The ability to adapt to exercise training is maintained throughout life, irrespective of sex and presence of disease. While training load (volume × intensity) is a suitable predictor of changes in mitochondrial content and VOmax, this relationship is less clear for capillary adaptations.
骨骼肌线粒体和毛细血管对有氧适能至关重要，其水平受抑制与慢性疾病和年龄相关疾病有关。目前，基于证据的增强这些特征的运动训练建议有限。探索诸如健康水平、年龄、性别和疾病等因素如何影响线粒体和毛细血管对不同运动刺激的适应性至关重要。
本研究的主要目的是比较低强度或中等强度持续耐力训练（ET）、高强度间歇或持续训练（HIT）以及冲刺间歇训练（SIT）对骨骼肌线粒体含量和毛细血管化变化的影响。其次，研究对最大摄氧量（VO₂max）、肌纤维横截面积和纤维类型比例的影响。
在PubMed、Web of Science和SPORTDiscus数据库中进行了系统的文献检索，检索截至2022年2月2日，无数据限制。纳入了ET、HIT和SIT的运动训练干预研究，前提是这些研究有至少一项线粒体含量或毛细血管化标志物的基线和随访测量数据。本综述的线粒体和毛细血管定量综合分析分别纳入了353篇和131篇研究文章中5973名参与者的数据。此外，还从这些研究中提取了VO₂max、肌纤维横截面积和纤维类型比例的测量数据。
在调整了相关协变量，如训练频率、干预周数和初始健康水平后，运动训练后线粒体含量的百分比增加在ET（23±5%）、HIT（27±5%）和SIT（27±7%）中增加程度相似（P>0.138），且不受年龄、性别、绝经、疾病或参与的肌肉量的影响。较高的训练频率（每周6次>4次>2次）与线粒体含量的更大增加相关。每运动总小时数，SIT增加线粒体含量的效率约为HIT的2.3倍，约为ET的3.9倍，而HIT比ET效率约高1.7倍。在调整干预周数和初始健康水平后，每根纤维的毛细血管数量在ET（15±3%）、HIT（13±4%）和SIT（10±11%）中增加相似（P=0.556）。每毫米的毛细血管数量仅在ET（13±3%）和HIT（7±4%）后增加，ET后的增加幅度大于HIT和SIT（P<0.05）。这种差异与ET（6.5±3.5%）、HIT（8.9±4.9%）和SIT（11.9±15.1%）后肌纤维横截面积的增加相一致。毛细血管化的增加主要发生在训练的早期阶段（<4周），且仅在未训练至中度训练的参与者中观察到。I型肌纤维的比例不受运动训练影响（P>0.116），但ET和SIT表现出相反的效果（P=0.041）。VO₂max在ET、HIT和SIT中增加相似，尽管与ET和SIT相比，HIT有更大改善的趋势（P=0.082），而SIT每运动小时的增加幅度最大。较高的训练频率（每周6次>4次>2次）与VO₂max的更大增加相关。女性VO₂max的百分比增加幅度大于男性（P=0.008）。一般来说，较低的初始健康水平与线粒体含量、毛细血管化和VO₂max的更大百分比改善相关。SIT在训练早期改善线粒体含量和VO₂max方面特别有效，而ET和HIT在更多训练周数中显示出较慢但稳定的改善。
运动训练中线粒体含量、毛细血管化和VO₂max的变化幅度在很大程度上由初始健康水平决定，初始健康水平较低的个体变化更大。适应运动训练的能力在一生中都能保持，无论性别和疾病状况如何。虽然训练负荷（量×强度）是线粒体含量和VO₂max变化的合适预测指标，但这种关系在毛细血管适应方面不太明确。
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