Research Focus
Understanding Muscle Health Across Aging, Injury, and Adaptation
Dr. Hyldahl's research examines how skeletal muscle responds to damage, exercise, aging, disuse, and therapeutic interventions. The SMART Lab's work connects cellular and molecular mechanisms with human physiology, with a particular focus on muscle repair, inflammatory signaling, extracellular matrix remodeling, mitochondrial function, and strategies that may preserve muscle health.
Research Areas
Skeletal Muscle Aging & Regeneration
Understanding why aged skeletal muscle repairs differently after damage, with emphasis on macrophage responses, extracellular matrix remodeling, inflammatory signaling, and satellite cell activity.
Muscle Damage & Protective Adaptation
Studying the repeated bout effect, eccentric exercise-induced muscle damage, soreness, extracellular matrix remodeling, MAPK signaling, and the cellular mechanisms that protect muscle from future injury.
Heat Therapy, Disuse & Mitochondria
Testing whether passive heat stress and localized heat therapy can preserve vascular function, maintain mitochondrial capacity, and attenuate muscle atrophy during immobilization or disuse.
Exercise, Performance & Human Physiology
Examining muscle function and adaptation across demanding physiological settings, including ultra-endurance exercise, masters athletics, and recovery from strenuous performance.
Sex Differences in Muscle Response
Investigating how menstrual cycle phase and sex-related physiology influence skeletal muscle mitochondrial respiration, myofiber damage, and macrophage infiltration after injury.
Knee Health, Biomechanics & Rehabilitation
Collaborating on studies of running biomechanics, knee cartilage health, cytokines, and functional recovery in populations such as anterior cruciate ligament reconstruction patients.
Approaches & Methods
Human Muscle Biopsies
Direct assessment of skeletal muscle tissue before and after exercise, damage, heating, disuse, and recovery interventions.
Cellular & Molecular Biology
Analysis of macrophages, T cells, satellite cells, pericytes, extracellular matrix remodeling, inflammatory signaling, and gene expression.
Mitochondrial Physiology
Measurement of mitochondrial respiratory capacity, adaptation to heat stress, and metabolic responses in skeletal muscle.
Translational Human Studies
Interventions designed around exercise, passive heating, immobilization, injury recovery, and performance-relevant physiology.
Selected Work
Representative Publications
The studies below show the range of Dr. Hyldahl's work, from eccentric exercise and muscle repair to heat therapy, mitochondrial adaptation, sex-specific physiology, biomechanics, and human performance.
- Richey RE, Hyldahl RD, Kaiser BW, Geiger PC, Halliwill JR, Minson CT. 2026. Heat Therapy: Targeting Health, Disease, and Disability.
- Nelson WB, Pfeifer BS, Lovell AR, Marchant ED, et al. 2025. Menstrual cycle influence on skeletal muscle mitochondrial respiration in humans.
- Kaluhiokalani JP, Wallace TE, Ahmadi M, Marchant ED, et al. 2025. Six weeks of localized passive heat therapy elicits some exercise-like improvements in resistance artery function.
- Pfeifer B, King B, Ahmadi M, Kaluhiokalani JP, et al. 2024. Menstrual cycle phase differences in myofiber damage and macrophage infiltration following electrical stimulation-induced muscle injury.
- Hyldahl RD, Gifford JR, Davidson LE, Hancock CR, Hafen PS, Parcell AC, Mack GW. 2024. Physiological assessment of a 16 day, 4385 km ultra-endurance mountain bike race.
- Marchant ED, Hyldahl RD, Gifford JR, Nelson WB, Hancock CR. 2023. Passive Heat Stress Induces Mitochondrial Adaptations in Skeletal Muscle.
- Ahmadi M, Karlsen A, Mehling J, Soendenbroe C, Mackey AL, Hyldahl RD. 2022. Aging is associated with an altered macrophage response during human skeletal muscle regeneration.
- Hyldahl RD, Hafen PS, Nelson WB, Ahmadi M, Pfeifer B, Mehling J, Gifford JR. 2021. Passive muscle heating attenuates the decline in vascular function caused by limb disuse.
- Hafen PS, Abbott K, Bowden JA, Lopiano R, Hancock CR, Hyldahl RD. 2019. Daily heat treatment maintains mitochondrial function and attenuates atrophy in human skeletal muscle subjected to immobilization.
- Sorensen JR, Kaluhiokalani JP, Hafen PS, Deyhle MR, Parcell AC, Hyldahl RD. 2019. An altered response in macrophage phenotype following damage in aged human skeletal muscle.
- Hyldahl RD, Chen TC, Nosaka K. 2017. Mechanisms and Mediators of the Skeletal Muscle Repeated Bout Effect.
- Hyldahl RD, Nelson WB, Xin L, Welling T, Groscost L, Hubal MJ, Chipkin S, Clarkson PM, Parcell AC. 2015. Extracellular matrix remodeling and its contribution to protective adaptation following lengthening contractions in human muscle.
Explore the Lab's Publications
View journal articles, abstracts, and other scholarly work from Dr. Hyldahl and collaborators.