A randomized trial found that one 40-minute high-intensity interval workout temporarily increased a marker associated with new bone formation, while 16 weeks of regular HIIT helped overweight premenopausal women maintain bone mineral density.
By yourNEWS Media Newsroom.
A single high-intensity interval training session may trigger measurable activity associated with bone formation in premenopausal women, according to a randomized trial that also found regular HIIT helped participants preserve bone density over 16 weeks.
The peer-reviewed study involved 22 overweight premenopausal women who were randomly assigned either to an exercise group or a control group. Women in the exercise group completed 40-minute HIIT sessions three times a week for 16 weeks at 80% to 90% of their heart-rate reserve, while the control group continued its normal daily activities.
Researchers measured several blood markers associated with bone remodeling and metabolic signaling, including procollagen type 1 N-terminal propeptide, or P1NP, which is commonly used as an indicator of bone formation.
After the first 40-minute HIIT session, P1NP increased significantly, with the researchers reporting an estimated rise ranging from 8.29% to 20.52%. A similar increase was detected following the final acute workout after the 16-week training period.
The findings received renewed attention after a Sept. 28 report by mindbodygreen highlighted the potential implications for women before menopause, a population that has received less attention in exercise-and-bone research than postmenopausal women.
Bone is continually remodeled throughout life, with old tissue broken down and replaced by new bone. Bone mass typically peaks during early adulthood and tends to decline with age. For women, that loss can accelerate substantially after menopause as estrogen levels fall.
Researchers therefore wanted to determine whether vigorous exercise could influence bone remodeling before menopause, when maintaining bone mass may help provide a stronger foundation for later life.
The acute response involved more than P1NP.
Interleukin-6, or IL-6, increased after exercise by an estimated 13.39% to 28.03%, while the bone-resorption marker CTX and adiponectin did not change significantly immediately after the workout.
IL-6 is a cytokine that can be released by contracting skeletal muscles during exercise. Although chronically elevated IL-6 is frequently associated with inflammation, its biological effects vary considerably depending on where it originates, how long it remains elevated and the physiological setting.
In the study, researchers found that the increase in P1NP was associated with changes in exercise-related signaling molecules, particularly IL-6, leading them to propose that muscle contraction may have stimulated processes involved in new bone formation.
The relationship does not prove that IL-6 caused the increase in bone formation, however. The researchers described the mechanism as a possibility rather than an established causal pathway.
That caution is consistent with the longer scientific debate over IL-6 and bone metabolism.
Earlier research has implicated IL-6 in increased bone resorption under conditions such as estrogen deficiency, while exercise research suggests short-lived IL-6 released from contracting muscles can have very different metabolic effects. The newer trial therefore does not overturn earlier findings but suggests that the context in which IL-6 is produced matters.
The 16-week portion of the study provided another notable result.
Women assigned to HIIT generally maintained their bone mineral density at the distal tibia, femur and lumbar spine. By contrast, the control group experienced a decline in tibial bone mineral density accompanied by an increase in resting CTX, a marker associated with bone breakdown.
The exercise group also showed higher resting adiponectin after completing the program, although researchers found that change was not associated with either bone biomarkers or bone mineral density.
Those findings suggest regular HIIT may help preserve bone during premenopause, but they do not demonstrate that the exercise increased overall bone density or prevented fractures.
Bone mineral density is widely used to assess skeletal strength and osteoporosis risk, but it is a surrogate measurement. The 16-week study was too small and too short to determine whether HIIT ultimately reduces fractures or osteoporosis later in life.
The trial also examined a narrow population: overweight premenopausal women. Its findings therefore cannot automatically be generalized to women of all body weights, postmenopausal women, men or people with existing osteoporosis.
The small sample of 22 participants is another important limitation.
Nevertheless, the results add to a larger body of evidence showing that mechanical loading from exercise influences bone remodeling. Weight-bearing impact activities and resistance exercise are already widely recognized as important components of maintaining skeletal health.
The study is particularly notable because it captured changes after just one workout.
The temporary P1NP increase does not mean participants created a clinically meaningful amount of new bone after 40 minutes. Rather, it indicates that biological processes associated with bone formation were activated following exercise.
Whether repeated episodes of that response translate into stronger bones over many years remains a separate question.
The longer-term results offer some support for that possibility because bone density remained stable in the exercise group while tibial density declined among controls.
The mindbodygreen report suggested two to three HIIT sessions weekly, along with impact exercise such as running and jumping and resistance training, as general strategies for supporting bone health. Those recommendations extend beyond what the trial itself established.
The study’s actual intervention consisted of three supervised 40-minute sessions per week at 80% to 90% of heart-rate reserve.
HIIT typically alternates demanding periods of exercise with lower-intensity recovery periods. Fitness authors have long promoted the method because it allows substantial cardiovascular work to be compressed into relatively short sessions.
Other exercise literature has also examined HIIT for metabolic fitness, muscle function and cardiovascular health, while resistance exercise provides a different form of mechanical loading that can stimulate both muscle and bone.
Researchers increasingly view muscle and bone as interconnected tissues rather than independent systems. Contracting muscle places physical force on bone while simultaneously releasing signaling molecules that may affect bone cells.
That muscle-bone communication is one reason the IL-6 finding attracted particular interest.
Still, the researchers stopped well short of describing HIIT as a treatment for osteoporosis.
Their conclusion was narrower: muscle contraction during a 40-minute HIIT session elevated IL-6 and was accompanied by increased P1NP, suggesting a possible enhancement of bone formation, while 16 weeks of training preserved bone density in the women studied.
For premenopausal women, the findings underscore a broader principle of bone health: the years before menopause may provide an important opportunity to preserve skeletal strength before age-related and estrogen-related bone loss accelerates.
The trial suggests high-intensity exercise could be one tool for doing that, but larger and longer studies will be needed to determine how much HIIT is optimal, whether the effect persists for years and, most importantly, whether it ultimately translates into fewer fractures later in life.
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