A claim you hear on longevity podcasts
The claim checked: HIIT makes the body build healthier, more efficient mitochondria Hear it at 11:22
Eight of ten studies found interval training raised mitochondrial content or function, up 49% to 69% in one. Two saw no change in some setups, like fasted exercise.
Computed from 10 studies that test this point, each judged by two readers, in full. 2 more studies are waiting for a full read and do not count yet.
“Just like strength training tells your muscles we need more power, HIIT tells your heart, lungs, and blood vessels, and your mitochondria, we need to become more efficient. Your body responds by building healthier mitochondria,”
trial or observed group · 2008 · landmark
“The maximal activities of CS and β-HAD and the total protein content of PDH were increased after training, but there were no differences between groups”
Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans. J Physiol
Who: Active but untrained young adults (23 ± 1 years)
PMID 17991697
trial or observed group · 2017 · landmark
“HIIT increased maximal absolute mitochondrial respiration in young (+49%) and older adults (+69%), whereas a significant increase following CT was observed in young (+38%), but not older adults (Figures 3B and 3D).”
Enhanced Protein Translation Underlies Improved Metabolic and Physical Adaptations to Different Exercise Training Modes in Young and Old Humans. Cell Metab
Who: Sedentary healthy young (18-30 years) and older (65-80 years) adults, Mayo Clinic
PMID 28273480
pooled analysis · 2025 · landmark
“Using pooled data from the five mitochondrial content markers (mito pooled ; comprising MvD, CS, SDH, COX, and HADH measurements), and adjusting for covariates (intervention weeks, training frequency, initial fitness level, active muscle mass while training, disease status, sex, and age) with appropriate weighting, all training intensity categories displayed significant increases in mitochondrial content (ET, 22.7 ± 4.6%; HIT, 27.0 ± 5.1%; SIT, 27.0 ± 6.7%; all P < 0.001; model 3).”
Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression. Sports Med
Who: Pooled human exercise-training groups (untrained, moderately trained and well-trained; healthy and diseased, mean age ~25-39 years, 74-97% men) doing low/moderate-intensity continuous endurance training (ET, below second ventilatory threshold/4 mmol/L lactate), high-intensity interval training (HIT) or sprint interval training (SIT), with muscle biopsies
PMID 39390310
trial or observed group · 2017
“The major novel finding of the present study was that interval compared to continuous single‐leg cycling, matched for total work and session duration, elicited greater increases in mitochondrial content in human skeletal muscle.”
Superior mitochondrial adaptations in human skeletal muscle after interval compared to continuous single-leg cycling matched for total work. J Physiol
Who: 10 healthy, habitually active young men (23 +/- 1 yr), one leg trained with HIIT
PMID 27396440
other primary study · 2014
“The maximal activity of citrate synthase increased by ∼40% after training (Fig. 3A, main effect for time, p<0.001).”
Three minutes of all-out intermittent exercise per week increases skeletal muscle oxidative capacity and improves cardiometabolic health. PLoS One
Who: 14 overweight/obese but otherwise healthy sedentary men and women (7 each; age 29±9 y)
PMID 25365337
controlled trial · 2019
“Furthermore, SET increased expression of markers of mitochondrial content and up-regulated content of MFN2, DRP1, and ANT1.”
High-intensity exercise training enhances mitochondrial oxidative phosphorylation efficiency in a temperature-dependent manner in human skeletal muscle: implications for exercise performance. FASEB J
Who: Healthy recreationally active men aged 18-40 yr, VO2max 45-55 ml/min/kg, BMI 19-26
PMID 31136218
controlled trial · 2018
“Subsarcolemmal mitochondrial volume was increased by high-intensity interval ( P = 0.02), but not endurance, training ( P = 0.79).”
High-intensity interval, but not endurance, training induces muscle fiber type-specific subsarcolemmal lipid droplet size reduction in type 2 diabetic patients. Am J Physiol Endocrinol Metab
Who: 16 sedentary type 2 diabetic patients (57±7 years old)
PMID 30016151
controlled trial · 2018
“High intensity training elicits stronger beneficial effects on physical fitness, basal RER, insulin sensitivity, and muscle mitochondrial content, as compared to continuous aerobic training.”
High intensity interval training is associated with greater impact on physical fitness, insulin sensitivity and muscle mitochondrial content in males with overweight/obesity, as opposed to continuous endurance training: a randomized controlled trial. J Musculoskelet Neuronal Interact
Who: 16 sedentary overweight/obese men aged 42-57, BMI 28-36, at risk for type 2 diabetes (HbA1c <6.5%)
PMID 29855444
controlled trial · 2018
“In addition, high‐intensity exercise seems to compensate for reduced exercise volume in the induction of mitochondrial biogenic molecular responses only when the intense exercise elicits marked metabolic perturbations.”
Metabolic stress-dependent regulation of the mitochondrial biogenic molecular response to high-intensity exercise in human skeletal muscle. J Physiol
Who: 12 endurance-trained men (amateur cyclists/triathletes, mean age 31.9, VO2max 61 mL/kg/min)
PMID 29727016
controlled trial · 2014
“We did not observe an increase in rates of MitoPS or a change in PGC-1α nuclear localization after exercise performed in the fasted state.”
Influence of aerobic exercise intensity on myofibrillar and mitochondrial protein synthesis in young men during early and late postexercise recovery. Am J Physiol Endocrinol Metab
Who: 8 healthy recreationally active young men (21 ± 1 yr, VO2peak 46.7 ml/kg/min)
PMID 24595306
None.
Four of seven studies found resistance training raised mitochondrial content or function; a low-volume program in older adults found no gain.
Computed from 7 studies that test this point, each judged by two readers, in full. 10 more studies are waiting for a full read and do not count yet.
other primary study · 2015 · landmark
“Collectively, these findings demonstrate that chronic RET improves mitochondrial respiratory function within skeletal muscle.”
Resistance Exercise Training Alters Mitochondrial Function in Human Skeletal Muscle. Med Sci Sports Exerc
Who: 11 young healthy untrained men (26±5 years)
PMID 25539479
controlled trial · 2013
“The first significant finding of this investigation was the clear demonstration of an RT-induced increase in mitochondrial content in the skeletal muscle of T2D individuals after 9 months of training.”
Nine months of combined training improves ex vivo skeletal muscle metabolism in individuals with type 2 diabetes. J Clin Endocrinol Metab
Who: 52 sedentary men and women with type 2 diabetes, aged 57.6 ± 7.5 y (HART-D ancillary)
PMID 23463651
trial or observed group · 2020
“In conclusion, the results of this study showed that 10 weeks of RT increased mitochondrial protein content and markers of mitochondrial dynamics, although no changes in these markers were detected following the first training bout.”
Acute and chronic effects of resistance training on skeletal muscle markers of mitochondrial remodeling in older adults. Physiol Rep
Who: 16 untrained older adults (6 men, 10 women, age 59 +/- 4)
PMID 32748504
controlled trial · 2026
“This study demonstrates that a combined resistance- and interval-type training program improves aerobic capacity, muscle strength, lean mass, and mitochondrial capacity in middle-aged and older adults.”
Resistance-based training improves mitochondrial capacity and redox balance in aging adults, independent of polyphenol supplementation. Redox Biol
Who: adults aged 55-70 (21 men, 20 women) doing supervised training with polyphenol or placebo supplement
PMID 41496202
trial or observed group · 2017 · landmark
“RT did not increase mitochondrial respiration significantly in either age group.”
Enhanced Protein Translation Underlies Improved Metabolic and Physical Adaptations to Different Exercise Training Modes in Young and Old Humans. Cell Metab
Who: Sedentary healthy young (18-30 years) and older (65-80 years) adults, Mayo Clinic
PMID 28273480
controlled trial · 2010
“In this pilot study, resistance training was highly effective in enhancing mitochondrial content in patients with moderate-to-severe CKD.”
Resistance training increases muscle mitochondrial biogenesis in patients with chronic kidney disease. Clin J Am Soc Nephrol
Who: 23 adults (mean age 64 ± 10 years) with CKD stages 3 and 4 on a low-protein diet (~0.6 g/kg/day)
PMID 20498251
controlled trial · 2016
“In summary, the results of this study indicate that a low volume resistance exercise intervention does not increase skeletal muscle oxidative capacity or reduce mitochondrial ROS production in older adults.”
Resistance exercise training and in vitro skeletal muscle oxidative capacity in older adults. Physiol Rep
Who: Nonobese sedentary to recreationally active men aged 60+, free of overt chronic disease
PMID 27405968
The Precis Weekly
One email a week with the claims and episodes we checked, what the studies found and the minute each claim was said.
Free. Unsubscribe anytime.