50 Hops a Day for Six Months: What Happened to Bone Density?

For postmenopausal women concerned about bone density, impact exercise is often recommended as a way to stimulate bone growth. But does jumping or hopping actually improve bone density after menopause? And what happens to the knees when we repeatedly expose them to higher-impact forces?

These are important questions, particularly for women with osteopenia who want to prevent further bone loss but may also have concerns about joint health.

A 2020 study by Hartley and colleagues, published in the Journal of Bone and Mineral Research, investigated both questions.

Researchers examined whether six months of progressive, single-leg hopping could improve bone density at the hip without negatively affecting knee cartilage.

The results were encouraging: women increased bone density in the exercised hip, while researchers found no evidence that the hopping program accelerated knee-joint damage.

However, understanding who participated, what the exercise actually involved, and who was excluded is essential before applying these findings to everyone with low bone density.

Who Participated in the Study?

Researchers recruited 42 postmenopausal women from the community, with 35 completing the six-month follow-up assessments.

Participants were between 55 and 70 years old, with an average age of 61.7 years. On average, they were approximately 10.6 years past menopause.

To participate, women needed to:

• Be between 55 and 70 years old.
• Be at least 12 months postmenopausal, with eligibility also accounting for relevant surgical or hormonal circumstances.
• Be medically capable of participating in high-impact exercise.
• Be able to complete the required imaging assessments.
• Meet the study’s bone-health and physical-activity screening requirements.

What About Women With Osteopenia?

This is an especially important distinction.

The participants had an average femoral-neck T-score of approximately −1.0, which is right around the threshold for osteopenia.

For reference:

• Normal bone density: T-score of −1.0 or higher.
• Osteopenia: T-score between −1.0 and −2.5.
• Osteoporosis: T-score of −2.5 or lower.

Although the study was not exclusively conducted in women with osteopenia, it included women with reduced bone density and provides evidence relevant to this population.

This makes the study particularly interesting because previous investigations of impact training in postmenopausal women have produced inconsistent results.

Who Was Excluded?

The researchers were selective about who could participate.

Women were excluded if they:

• Met national criteria for osteoporosis medication treatment.
• Had a symptomatic knee, hip, or back injury.
• Had medical conditions that made participation in high-impact exercise inappropriate, such as certain heart conditions or hypertension.
• Had a body mass index (BMI) greater than 30.
• Already performed exercise involving forces greater than jogging more than once per week.
• Were taking medications known to affect bone density or bone metabolism.
• Had participated in a study involving ionizing radiation within the previous 12 months.
• Had contraindications to MRI or DXA scanning.

These exclusions matter.

The study was designed to investigate how relatively healthy postmenopausal women responded to high-impact training. It was not designed to establish whether the same program would be appropriate for someone with advanced osteoporosis, previous fragility fractures, substantial joint pain, or significant physical limitations.

Many adults beginning an exercise program have combinations of these considerations. That does not necessarily mean impact exercise is inappropriate, but it does mean the exercise must be selected and progressed according to the individual.

How Was the Study Designed?

One of the more interesting aspects of this research was its use of a unilateral exercise program.

Rather than dividing the women into separate exercise and control groups, researchers randomly assigned one leg to perform the hopping intervention.

The opposite leg served as the control.

This allowed researchers to compare changes in bone density between the two hips within the same person.

Because both legs belonged to the same individual, factors such as genetics, hormonal status, nutrition, and most daily activities were shared between them.

If bone density improved more in the exercised hip than the non-exercised hip, it would provide evidence that the additional mechanical loading contributed to the difference.

Researchers used DXA scans to assess bone density and bone-related structural measurements. They also performed MRI scans of both knees to evaluate cartilage composition, cartilage defects, and bone marrow lesions.

What Exactly Is a Hop?

Before discussing the exercise protocol, it’s worth defining what researchers meant by hopping.

A hop is a movement in which a person takes off from one foot and lands back on that same foot.

This differs from a traditional two-legged jump, in which both feet typically leave and contact the ground together.

For example:

• A vertical hop involves pushing off one foot, briefly leaving the ground, and landing on that same foot.
• A forward hop involves taking off and landing on the same foot while moving forward.
• A lateral hop involves hopping sideways and landing on the same foot.
• A rotational hop involves changing body orientation during the movement.

Because a hop is performed on one leg, the landing forces are concentrated through that leg rather than being distributed across both legs.

This distinction is important because the magnitude and distribution of mechanical loading influence how bone responds to exercise.

However, single-leg hopping also requires greater balance, coordination, strength, and landing control than many two-legged movements.

What Did the Exercise Program Involve?

The intervention lasted six months and gradually progressed toward 50 hops per day.

Importantly, participants did not begin with 50 high-intensity hops every day.

Researchers increased the number of repetitions, training frequency, movement directions, and hopping height during the initial ten weeks.

The program progressed approximately as follows:

Training period	Exercise prescription
Week 1	18 low vertical hops, 3 days/week
Weeks 2–3	Increased to 24–30 hops, 3 days/week
Weeks 4–6	Up to 40 hops, 3–4 days/week
Weeks 7–10	Progressed to 50 hops, 5–6 days/week
Weeks 11–26	50 multidirectional hops, daily

By week 11, the prescribed program included five sets of ten hops, separated by approximately 15 seconds of rest.

The final protocol included vertical, forward/backward, lateral, and rotational hops.

Participants were encouraged to increase hopping height as their abilities improved.

They also received exercise demonstrations, had access to a demonstration video, could use sturdy support for balance, and were offered weekly group sessions and ongoing contact with researchers.

The actual hopping portion took approximately three to four minutes. Including warm-up and cooldown, the daily routine required less than 15 minutes.

This relatively small time commitment is one reason the findings are interesting. The intervention produced measurable differences in bone outcomes without requiring lengthy exercise sessions or specialized equipment.

Did Hopping Improve Bone Density?

Yes.

After six months, researchers found statistically significant differences between the exercised and control legs.

Femoral-Neck Bone Mineral Density

The femoral neck is the narrower section of bone connecting the femoral head to the shaft of the thighbone. It is a particularly important area because fractures here can have serious consequences for independence and mobility in older adults.

The results showed:

Measurement	Exercised leg	Control leg
Femoral-neck bone mineral density	+0.81%	−0.57%
Femoral-neck bone mineral content	+0.69%	−0.71%
Section modulus (estimated bending strength)	+3.18%	−0.75%

The difference in bone-density change between the legs was approximately 1.38 percentage points.

Although these percentages may appear small, bone density generally changes slowly, and maintaining or modestly increasing bone density after menopause can be meaningful.

The improvement in section modulus was also interesting.

Section modulus is a structural measurement related to a bone’s ability to resist bending. Bone strength depends on more than mineral density alone. Bone geometry and the distribution of mineral also contribute to its resistance to mechanical forces.

However, section modulus is an estimated structural measurement, not a direct test of actual fracture resistance.

What About the Spine?

The findings were not equally encouraging at every skeletal site.

Lumbar spine bone mineral density decreased approximately 0.9% during the study.

This suggests that although hopping provided a useful stimulus to the hip, it did not prevent bone loss at the lumbar spine during the intervention.

Bone adaptation is site-specific.

An exercise that loads one area effectively does not necessarily produce the same benefits throughout the skeleton.

This is one reason a comprehensive bone-health program should involve more than one exercise modality.

Did Hopping Damage the Knee Cartilage?

This was another important part of the study.

Researchers used MRI imaging to evaluate changes in knee cartilage and other joint features associated with osteoarthritis.

They examined cartilage composition using T2 mapping, an MRI technique that provides information related to cartilage water content and its collagen structure.

They also assessed cartilage defects and bone marrow lesions, which can be associated with joint degeneration.

Interestingly, many participants already had detectable knee abnormalities at baseline despite being relatively healthy and not reporting symptomatic knee injuries.

After six months, researchers found no significant evidence that the hopping intervention accelerated deterioration in the measured knee-joint structures compared with the control leg.

Some cartilage defects and bone marrow lesions progressed during the study, while others improved. However, these changes occurred in both the exercise and control knees, without significant differences attributable to the hopping intervention.

This does not prove that hopping can never damage cartilage or that all forms of high-impact exercise are safe for every individual.

It does suggest that appropriately selected postmenopausal women can tolerate progressive high-impact loading without necessarily causing measurable deterioration in knee-joint structures over six months.

How Does This Compare With Research on Knee Osteoarthritis?

This study builds on research we previously discussed involving postmenopausal women with knee osteoarthritis.

In a 2017 study by Multanen and colleagues, researchers investigated 12 months of progressively increased high-impact exercise in women with mild knee osteoarthritis.

That study found improvements in estimated femoral-neck structural strength without measurable deterioration in the biochemical composition of the load-bearing knee cartilage.

You can read our detailed review here:

Is Jumping Really Bad for Your Knees? What Research Reveals About Cartilage, Bone Strength, and Muscular Strength

Although the studies investigated similar questions, there were several meaningful differences.

Different Participant Populations

The Multanen study specifically recruited women with diagnosed, symptomatic, mild knee osteoarthritis.

The Hartley study recruited relatively healthy postmenopausal women, including women with osteopenia, but excluded those with symptomatic knee, hip, or back injuries.

The two studies therefore provide information about different populations.

Different Bone-Health Measurements

Both studies investigated skeletal responses to impact exercise, but they emphasized somewhat different outcomes.

The Multanen study focused on changes in femoral-neck structural strength, particularly a measurement estimating the bone’s resistance to bending.

The Hartley study directly demonstrated improvements in femoral-neck bone mineral density measured by DXA, along with changes in bone mineral content and estimated bending strength.

This is an important addition to the evidence because improving actual bone mineral density is a central goal of many exercise programs for women with osteopenia.

Different Exercise Programs

The Multanen study involved 12 months of supervised high-impact aerobic and step-aerobic exercise, including progressive jumping.

The Hartley study used six months of predominantly home-based, single-leg hopping.

Together, the studies suggest that appropriately prescribed impact training can produce favorable adaptations in bone while not necessarily accelerating measurable knee-cartilage deterioration.

However, neither study establishes that jumping is appropriate for every person with osteoporosis or osteoarthritis.

What About Injuries and Exercise Tolerance?

Although the bone and imaging outcomes were encouraging, not everyone tolerated the exercise program.

Two participants withdrew from follow-up because of knee discomfort, while another withdrew because of Achilles tendinopathy.

An additional participant stopped the intervention because of knee discomfort but returned for follow-up testing.

The knee symptoms associated with exercise resolved after stopping, while the Achilles injury required physiotherapy.

Among participants completing follow-up, average adherence during the final 16 weeks was approximately 77%.

These findings are a useful reminder that a program can produce positive average results while still being inappropriate or uncomfortable for certain individuals.

The absence of significant cartilage deterioration does not mean the exercises were entirely risk-free.

What If You Cannot Hop When You First Start Exercising?

This may be one of the most important practical considerations when applying the research.

Not everyone has the strength, balance, coordination, or physical capacity to perform repeated single-leg hops when beginning an exercise program.

For some individuals, even standing on one leg for several seconds can be challenging.

Others may struggle with calf strength, knee control, landing mechanics, or confidence.

This is particularly relevant for adults who have spent years being relatively sedentary, have experienced falls, or are managing multiple orthopedic considerations.

Although the researchers progressively increased hopping volume and intensity, their program still required participants to have a baseline level of physical capability.

The findings should not be interpreted as a recommendation for everyone with osteopenia to immediately begin hopping.

Building the Capacity for Impact

At Fit Alliance, we believe exercise should meet people where they are.

For someone who is not ready to hop, preparation might focus on:

1. Developing lower-body strength. Exercises targeting the quadriceps, hamstrings, glutes, and calf muscles can improve the ability to generate and absorb force.
2. Improving single-leg balance. Supported balance exercises can help develop stability and confidence.
3. Building functional strength. Sit-to-stands, step-ups, and other appropriately selected movements can improve everyday physical capacity.
4. Developing movement control. Learning to control faster movements, changes of direction, and deceleration can help prepare someone for more dynamic activities.
5. Introducing appropriate impact. Depending on the person’s medical history and capabilities, this might begin with carefully controlled lower-level impact before eventually progressing to small hops or jumps.

These preparatory exercises are not necessarily equivalent to the bone-loading stimulus produced by the hopping program.

Rather, they can help someone develop the capabilities needed to tolerate more challenging exercise.

For some individuals, higher-impact training may eventually become appropriate.

For others, certain forms of impact may remain unsuitable because of fracture risk, joint limitations, or other health considerations.

The objective is not simply to make everyone jump. It is to identify the most effective loading strategy that an individual can perform safely and consistently.

Why Hopping Alone Is Not a Complete Bone-Health Program

Although this study demonstrated favorable changes in femoral-neck bone density, there were other important findings.

The intervention did not significantly increase lean body mass.

Additionally, lumbar spine bone density declined during the six-month period.

These findings reinforce the importance of combining different forms of exercise.

Progressive resistance training can help improve muscle strength, maintain or increase muscle mass, and provide mechanical loading to skeletal regions that may not receive sufficient stimulus from hopping alone.

Balance and functional training can help reduce fall risk and improve the ability to navigate everyday activities.

Impact exercise, when appropriate, can provide a different mechanical stimulus that may contribute to maintaining or improving bone density at certain skeletal sites.

No single exercise addresses every aspect of bone health, muscle health, physical function, and fall prevention.

A comprehensive approach should consider all of them.

Important Limitations of the Study

There are several reasons to interpret the findings with appropriate caution.

First, the study was relatively small, with only 35 women completing follow-up assessments.

Second, the six-month duration provides information about short-term responses but does not establish whether the improvements would continue, plateau, or reverse over subsequent years.

Third, the participants were selectively screened. These results cannot automatically be generalized to women with more advanced osteoporosis, a history of fragility fractures, symptomatic joint problems, or other significant limitations.

Fourth, the study did not measure whether participants experienced fewer hip fractures. Changes in bone density and estimated bone strength are encouraging, but they do not directly establish a reduction in fracture risk.

Finally, the differences in BMD were modest. Individual DXA measurements have inherent variability, so a small percentage change should not automatically be interpreted as a clearly measurable improvement in any one person’s clinical scan.

These limitations do not eliminate the value of the findings. They help clarify what the research actually demonstrates.

Final Thoughts: Stronger Bones Require the Right Kind of Stress

The Hartley study provides encouraging evidence that progressive high-impact exercise can improve hip bone density in postmenopausal women without necessarily damaging knee cartilage.

However, hopping isn’t the right starting point for everyone. Strength, balance, coordination, and individual health considerations should determine when and how impact exercises are introduced.

At Fit Alliance, we combine progressive resistance training, balance exercises, and appropriate impact training to help adults 50+ improve bone health, build strength, and maintain independence.

Interested in improving your strength and bone health?

Fit Alliance offers personal training and Small Group Personal Training at our Tigard and Beaverton locations, specifically designed for adults 50+.

References

Hartley C, Folland JP, Kerslake R, Brooke-Wavell K. (2020). High-impact exercise increased femoral neck bone density with no adverse effects on imaging markers of knee osteoarthritis in postmenopausal women. Journal of Bone and Mineral Research, 35(1), 53–63. 

Multanen J, Rantalainen T, Kautiainen H, et al. (2017). Effect of progressive high-impact exercise on femoral neck structural strength in postmenopausal women with mild knee osteoarthritis: a 12-month RCT. Osteoporosis International, 28(4), 1323–1333.