How to Train According to the Experts

1:18:45 Brady Holmercontradictedmoderate

Meta-analyses demonstrate that high-intensity interval training increases mitochondrial content and carnitine palmitoyltransferase enzyme levels and activity more than low- to moderate-intensity training.

"And the evidence is pretty clear based on what I've been reading in certain meta-analyses that would show high-intensity training compared to moderate- or low-intensity training, it increases mitochondrial content more, it increases CPT enzyme levels and activity more so, and it also leads to better fat oxidation capacity." (said at 1:18:45)

Meta-analytic evidence does not show that high-intensity interval training (HIIT) increases skeletal muscle mitochondrial content significantly more than low- to moderate-intensity continuous endurance training. A large systematic review and meta-regression of 353 studies (PMID: 39390310) found that adjusted percentage increases in skeletal muscle mitochondrial content were similar across endurance training (23%), high-intensity training (27%), and sprint interval training (27%) (p > 0.138). While interval modalities were significantly more time-efficient per hour of exercise, total mitochondrial biogenesis was comparable. Furthermore, meta-analyses comparing HIIT and moderate-intensity continuous training for fat oxidation show either equivalent outcomes (PMID: 37701124) or very small differences (PMID: 35859145), and no meta-analysis confirms superior CPT enzyme levels or activity for HIIT over moderate-intensity training.

partial: Effects of high-intensity interval training (HIIT) and sprint interval training (SIT) on f… (British journal of sports medicine 2022) · cited 76x in the literature
"HIIT and/or SIT were slightly more effective than MICT (MD=0.03; 95% CI 0.01 to 0.05; p =0.005)." (abstract, results, passage verified)
pubmed full study (doi)
contradicts: Chronic high-intensity interval training and moderate-intensity continuous training are bo… (Journal of exercise science and fitness 2023) · cited 27x in the literature
"When analyzing studies that have directly compared HIIT and MCIT in obese people, it seems there is no difference in the MFO change (MD = 0.01; 95%CI [-0.02 to 0.04]; I 2 = 64%)." (abstract, results, passage verified)
pubmed full study (doi)
contradicts: Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscl… (Sports medicine (Auckland, N.Z.) 2025) · cited 108x in the literature
"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)" (abstract, results, passage verified)
pubmed full study (doi)

2:09:55 Brady Holmercontradictedmoderate

Resistance training does not produce the same cardiovascular adaptations as aerobic exercise, such as improvements in endothelial function, cardiovascular structure, and blood pressure.

"So if you, you know, if you look at all the benefits of aerobic exercise training that include like improvements in endothelial function, cardiovascular structure, like we talked about, blood pressure, you don't get those same benefits from resistance exercise training." (said at 2:09:55)

The claim that resistance training does not produce improvements in cardiovascular parameters such as endothelial function and blood pressure is contradicted by systematic reviews and meta-analyses of randomized controlled trials. A meta-analysis of 23 trials (PMID 34399984) demonstrated that resistance training significantly improves endothelial function, measured by brachial artery flow-mediated dilation (mean difference 2.39%, 95% CI 1.65 to 3.14), across healthy adults and individuals with cardiovascular or metabolic diseases. Furthermore, resistance training is well-documented to elicit meaningful reductions in resting blood pressure. While the morphological patterns of cardiac structural adaptation can differ between endurance exercise (predominantly eccentric remodeling/chamber dilation) and resistance training (predominantly concentric remodeling/wall thickening), resistance training robustly provides distinct vascular, hemodynamic, and endothelial benefits.

contradicts: Effects of resistance training on endothelial function: A systematic review and meta-analy… (Atherosclerosis 2021) · cited 74x in the literature
"Resistance training improves FMD in healthy individuals and patients with cardiovascular and metabolic diseases." (abstract, conclusions, passage verified)
pubmed full study (doi)

How to Train According to the Experts

Contradicted by research

Meta-analyses demonstrate that high-intensity interval training increases mitochondrial content and carnitine palmitoyltransferase enzyme levels and activity more than low- to moderate-intensity training.

Resistance training does not produce the same cardiovascular adaptations as aerobic exercise, such as improvements in endothelial function, cardiovascular structure, and blood pressure.