Heat Therapy and Muscle Function Study

Summary

Exercise tolerance decreases with age and a sedentary lifestyle. Muscle critical power (CP), is a sensitive measure of exercise tolerance that is more even more relevant to and predictive of endurance performance than VO2max.

While recent evidence indicates that CP and muscle function decrease with aging, the cause of this decrease in CP and the best way to mitigate the decrease in CP are unknown.

This study will:

1. Measure knee extensor CP in young and old individuals and determine the extent to which changes in muscle oxygen delivery (e.g. resistance artery function, maximum exercise blood flow), muscle mass and composition (e.g. whole-muscle size, muscle fiber cross-sectional area) and mitochondrial oxygen consumption (e.g. maximal coupled respiration of permeabilized fibers biopsied from the knee extensors) contribute to the decrease in CP with age.
2. Examine the effectiveness of two different therapies (1. High Intensity Interval Training, HIIT and 2. Muscle Heat Therapy) at improving muscle function and critical power in young and older adults.
3. Examine the impact of muscle disuse (2 weeks of leg immobilization), a potential contributor to the decrease in muscle function with aging, on muscle function and critical power and determine if heat therapy is an effective means of minimizing the impact of disuse on muscle function and critical power.

Conditions

• Exercise Intolerance
• Aging
• Heat Therapy
• High Intensity Interval Training

Interventions

OTHER

High Intensity Interval Training of the Knee Extensors

Subjects will perform intense, single leg knee extension exercise 3 times a week for 6 weeks. Specifically, subjects will be seated in a custom knee extension ergometer and perform single leg, dynamic knee extension (similar to single leg cycling) as they perform the exercise. After a 6 minute warm-up at \~20% of that leg's maximum aerobic power (determined during a graded exercise test of single leg knee extension), subjects will perform 4 bouts of 4 minutes at \~80% of maximum aerobic power. Recovery of 4 minutes at \~40% will occur between each bout of exercise. A cool down will be provided at the end of exercise. In total, subjects will perform 40 minutes of single leg knee extension exercise, 3 times a week for 6 weeks. Maximum aerobic power (determined by a graded exercise test) will be determined again at 3 weeks to appropriately adjust the training intensity.

OTHER

Muscle Heat Therapy

Subjects will receive muscle heat therapy on the knee extensor muscles (short-wave diathermy) for 120 minutes for each visit. Specifically, subjects will lie supine while short-wave diathermy units (Megapulse II) will be placed on the quadriceps femoris and turned on to 800 pulses per second with a pulse duration of 400 microseconds. Our previous research (e.g. Hafen et al 2018- Repeated exposure to heat stress...) has indicated that this treatment raises muscle temperature to \~39C, a similar temperature induced by exercise.

OTHER

Muscle Disuse

Subjects will undergo 2 weeks of limb immobilization (a model of muscle disuse). Specifically, a knee brace will be placed on one of the subjects' legs and bent to a flexion of 60 degrees to prevent the foot from touching the ground while standing. Subjects will given a pair of crutches and asked to ambulate on crutches for 2 weeks, avoiding bearing any weight with the immobilized leg.

OTHER

Sham Heat Therapy

Specifically, subjects randomly assigned to the sham group will receive the same treatment as the heat group (same number of visits and set up with the heating units applied to leg for 2 hours each visit) except, unbeknownst to either group, the heating units will never be turned on for the sham group.

Sponsors & Collaborators

• Brigham Young University

  lead OTHER

Principal Investigators

• Jayson Gifford, Ph.D. · Brigham Young University

• Robert Hyldahl, Ph.D. · Brigham Young Univeristy

Study Design

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

SINGLE

Model

PARALLEL

Eligibility

Min Age

18 Years

Max Age

95 Years

Sex

ALL

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2021-04-01

Primary Completion

2024-12-31

Completion

2024-12-31

Countries

• United States

Study Locations