Lifting for Bone: Why Swim-Bike Athletes Need Impact and Load

Ask a triathlete why they lift weights and the usual answer is performance: a stronger run, a more durable bike leg, fewer injuries. All of these are reasonable, and TriForward covers them in "The Minimum Effective Dose" and "Jumps or Iron?". This article is about a different reason that gets less attention: your bones.

Two of triathlon's three sports are almost entirely non-weight-bearing. Many triathletes spend most of their training hours in the pool or on the bike, and some run relatively little, especially those who came to the sport from swimming or cycling, or who are managing an injury. Meanwhile, bone density declines with age for everyone, and particularly for women after menopause. The result is a group of very fit people who may have less bone than their fitness suggests.

This article covers why swimming and cycling don't build bone, what the trials of heavy lifting and jumping show (and who they studied), and how a triathlete can add impact and load without getting hurt.

How bone responds to load

Bone is living tissue that adapts to the forces placed on it. In broad terms, drawn from general bone physiology rather than a single study, it is thought to respond best to loads that are:

• High in magnitude, such as heavy lifting or landing from a jump.
• Fast, with a quick rise in force, as in jumping or hopping.
• Varied or unusual, in directions the bone doesn't usually experience.
• Short and intermittent, since bone is thought to become less responsive to many repetitions of the same load in a single session.

Running provides some of this, but in a repetitive, predictable pattern. Swimming and cycling provide very little: the water supports your body, the saddle supports your weight, and both involve smooth, repetitive forces rather than impacts.

What happens to cyclists' bones

A 2012 systematic review by Olmedillas and colleagues in BMC Medicine examined 31 studies on cycling and bone health. Their main conclusions:

• Road cycling doesn't appear to have a significant bone-building effect.
• Adult road cyclists in regular training often had low bone mineral density, particularly at the lumbar spine, although findings weren't entirely consistent.
• Mountain biking, or combining cycling with other sports, may lessen this effect.
• Diet and hormones didn't fully explain the findings. The authors suggested that long hours sitting on the bike, followed by recovery spent largely sitting or lying down, may play a part.

Most of the studies were cross-sectional and involved competitive male road cyclists. They show an association, not proof that cycling itself causes bone loss.

What happens to swimmers' bones

A 2013 systematic review by Gómez-Bruton and colleagues in PLoS ONE asked whether swimming affects bone. They included 64 studies, most of them cross-sectional, in children, adolescents and adults. They found:

• Swimmers generally had similar bone density to sedentary controls.
• Swimmers generally had lower bone density than athletes in high-impact sports.
• Swimmers showed higher bone turnover, which the authors suggested might relate to bone structure rather than density alone.
• The authors concluded swimming doesn't seem to harm bone, but isn't one of the best sports for building it, because of the low gravity and lack of impact in water.

That's a more reassuring picture than cycling: swimming doesn't appear to reduce bone density, but it doesn't build it either. Inference: if most of your training is swimming and cycling, you may be getting roughly the bone stimulus of a sedentary person from those hours, despite being very fit.

Why this matters for triathletes

TriForward's "Bone Stress Injuries in Triathletes" describes a survey of 86 German elite triathletes in which 23% reported at least one stress fracture. That article argues that swimming and cycling don't protect the skeleton the way athletes might assume. This is the other side of the same problem: if bone isn't built by most of your training, it may have less margin when the running load does arrive.

Inference: three groups of triathletes may be at particular risk:

• Former swimmers and cyclists who came to triathlon without a background in impact sports.
• Masters athletes, especially women around and after menopause, when bone loss accelerates. TriForward's "Menopause and the Triathlete" covers the wider evidence.
• Athletes who run little, because of injury, preference or a bike-heavy plan.

The LIFTMOR trial

For a long time, people with low bone density were advised to avoid heavy lifting and impact for fear of fractures. The LIFTMOR trial, led by Steven Watson and Belinda Beck at Griffith University and published in the Journal of Bone and Mineral Research in 2018, tested that assumption.

• Participants: 101 postmenopausal women aged around 65 (65 ± 5 years) with low bone mass, defined as a T-score below −1.0 at the hip or spine.
• Exercise group (49 women): twice-weekly, 30-minute supervised sessions of high-intensity resistance and impact training for 8 months. The exercises were deadlifts, back squats, overhead presses and jumping chin-ups with drop landings, building to 5 sets of 5 repetitions at more than 80 to 85% of one-repetition maximum.
• Control group (52 women): a home-based, low-intensity programme of light exercises and stretches.
• Introduction: the first month used bodyweight and low-load versions of the exercises to teach technique. Groups had no more than eight participants per instructor.

The results:

• Lumbar spine bone density rose by 2.9% in the exercise group and fell by 1.2% in the control group.
• Femoral neck bone density rose by 0.3% in the exercise group and fell by 1.9% in the control group.
• Femoral neck cortical thickness and functional performance improved more in the exercise group.
• There was one adverse event, a minor lower back spasm.
• Compliance was high: 92% in the exercise group.

The authors were cautious about how the results should be used. They emphasised that graduated loading, close supervision and attention to technique were key to safety, and they did not recommend unsupervised high-intensity training for people with low bone mass. Participants with recent fractures, back pain, uncontrolled heart disease and various bone-affecting conditions were excluded.

These were older women with low bone mass, not triathletes. Inference: the trial shows that heavy, well-coached lifting can be safe and effective for bone in a population that was traditionally steered away from it. A younger, fitter triathlete without osteoporosis is likely to tolerate it at least as well, though the size of the bone response may differ.

Hopping: how often?

A 2010 trial by Bailey and Brooke-Wavell in Bone looked at how often brief impact exercise needs to be done. It involved 61 healthy premenopausal women with a mean age of 34.

• The exercise was 50 multidirectional hops on one randomly selected leg. The other leg acted as a control.
• Women were randomised to hop 0, 2, 4 or 7 days per week for 6 months.
• Compliance was 87%.

Femoral neck bone density changes in the exercised leg were:

• 0 days per week: −0.3%
• 2 days per week: 0.0%
• 4 days per week: +0.9%, not clearly different from no change
• 7 days per week: +1.8%

The authors concluded that brief daily hopping increased femoral neck bone density, but less frequent hopping wasn't clearly effective. Inference: 50 hops takes about a minute. Frequency, not volume, appears to be what matters, which suits busy triathletes.

The cyclist jumping trial

The most directly relevant trial for swim-bike athletes is a 2024 study by Hilkens and colleagues in the International Journal of Sport Nutrition and Exercise Metabolism. It involved 36 elite road cyclists aged around 21, 8 men and 28 women, during the off-season.

• Intervention group (18 cyclists): five 5-minute jumping sessions per week for 18 weeks, each preceded by 15 g of hydrolysed collagen.
• Control group (18 cyclists): no intervention.

The results:

• Femoral neck bone density was preserved in the intervention group, while it fell in the control group.
• There was no difference between groups at the total hip, lumbar spine or whole body.

This trial is important because it was done in cyclists. But it has limits: it combined jumping with collagen, so the two effects can't be separated, and it was open-label, with no placebo. The benefit was maintenance of bone density at one site rather than a large gain.

What the guidelines say

A 2022 UK consensus statement led by Katherine Brooke-Wavell, published in the British Journal of Sports Medicine, set out exercise recommendations for people with osteoporosis or at risk of it:

• Resistance training on 2 to 3 days per week, using progressive loads of around 8 to 12 repetition maximum, building to 2 to 3 sets.
• Moderate impact exercise on most days, with at least 50 impacts per session, for those without vertebral fractures or multiple fractures. Brief bursts, such as 5 sets of 10 impacts, are an option.
• For people with vertebral fractures or multiple fractures, impact no higher than brisk walking, and avoiding loaded or repeated spinal flexion.
• Be active every day and avoid long periods of sitting.

The consensus found little evidence of significant harm from physical activity in these groups and concluded that the benefits generally outweigh the risks.

Putting it into practice

The following suggestions combine the trials and consensus above. They're inference for triathletes, not a tested programme:

1. Lift heavy twice a week. Use multi-joint exercises such as deadlifts, squats and overhead presses. Start with technique and light loads for several weeks, and progress towards heavier sets of around 5 repetitions as your technique allows. A coach or qualified instructor is worth paying for at the start.
2. Add short impact bouts most days. Start with 10 to 20 low hops or skips and build towards around 50 varied hops, jumps or bounds in different directions. These can be part of your warm-up before a run or a lifting session.
3. Progress gradually. Begin with two-footed jumps on a forgiving surface before moving to single-leg hops.
4. Keep it short. You don't need long sessions. LIFTMOR used 30 minutes, the hopping trial about a minute.
5. Don't replace running. For most triathletes, running remains the main source of impact.

TriForward's "Jumps or Iron?" and "Calf and Achilles Capacity" cover related programming for performance and tendon health.

Fitting it into a triathlon week

The biggest barrier for most triathletes isn't knowing what to do, it's finding the time. The good news is that bone-focused work is short. Some practical options, which are inference rather than tested schedules:

• Attach impact work to sessions you already do. A minute of hops or skips at the start of a run, or after a swim before you shower, adds almost no time.
• Place heavy lifting away from key sessions. Many triathletes lift on the same day as an easy swim, or after an easy ride, so that heavy legs don't compromise the next day's hard run or bike session.
• Keep lifting through the season. Bone adapts slowly, over months. Stopping lifting for the whole race season and restarting each winter means repeatedly starting from scratch.
• Reduce, don't drop, during race weeks. A lighter set of hops and a short, lighter lifting session can maintain the habit without adding fatigue.

Men and bone

Much of the bone research, and most public discussion, focuses on women, because bone loss accelerates around menopause. LIFTMOR and the hopping trial included only women, and the cyclist trial was mostly women. But the Olmedillas review of cycling studies was dominated by men, and low bone density in male road cyclists was one of its main findings.

The 2023 International Olympic Committee consensus on Relative Energy Deficiency in Sport (REDs), led by Margo Mountjoy, describes impaired bone health as one of the best-documented consequences of problematic low energy availability in both female and male athletes. Inference: a male triathlete who trains mainly on the bike, runs little and restricts food to stay light could combine several of the risk factors in this article without any obvious warning sign. Men shouldn't assume bone health is only a women's issue.

A triathlon scenario

The following example is illustrative, not drawn from a study. A 52-year-old woman who swam competitively as a teenager now trains for Olympic-distance triathlon. She swims three times a week, rides twice and runs twice for about 30 minutes. She has never lifted weights. A scan done for another reason shows osteopenia.

Based on the evidence above, she might:

• Discuss the scan with her doctor first, including whether further tests or medication are needed and whether there are any reasons to avoid impact.
• Find supervised strength coaching, ideally with someone experienced with low bone density, rather than copying LIFTMOR alone.
• Add short daily impact work, starting with low hops, if her clinician agrees.
• Keep running, progressing gradually.

Common mistakes

• Assuming fitness equals bone health. A high VO2max says nothing about bone density.
• Lifting light weights for many repetitions and expecting a bone response. The trials used heavy loads or impacts.
• Doing impact work once or twice a week. In the hopping trial, only daily hopping clearly worked.
• Jumping straight into heavy lifting without learning technique.
• Ignoring fuelling. Low energy availability impairs bone health in women and men. TriForward's "Under-Fuelled, Not Undertrained" covers this.

What we don't know

• Whether these programmes reduce fractures in triathletes. The trials measured bone density, not fractures.
• The bone response in younger, healthy triathletes. LIFTMOR studied older women with low bone mass.
• The effect of jumping alone in cyclists, since the cyclist trial combined it with collagen.
• The minimum effective dose for men, who were underrepresented in these studies.

References

• Olmedillas H, González-Agüero A, Moreno LA, Casajus JA, Vicente-Rodríguez G. Cycling and bone health: a systematic review. BMC Medicine, 2012;10:168. doi:10.1186/1741-7015-10-168
• Gómez-Bruton A, González-Agüero A, Gómez-Cabello A, Casajús JA, Vicente-Rodríguez G. Is bone tissue really affected by swimming? A systematic review. PLoS ONE, 2013;8(8):e70119. doi:10.1371/journal.pone.0070119
• Watson SL, Weeks BK, Weis LJ, Harding AT, Horan SA, Beck BR. High-intensity resistance and impact training improves bone mineral density and physical function in postmenopausal women with osteopenia and osteoporosis: the LIFTMOR randomized controlled trial. Journal of Bone and Mineral Research, 2018;33(2):211–220. doi:10.1002/jbmr.3284
• Bailey CA, Brooke-Wavell K. Optimum frequency of exercise for bone health: randomised controlled trial of a high-impact unilateral intervention. Bone, 2010;46(4):1043–1049. doi:10.1016/j.bone.2009.12.001
• Hilkens L, van Schijndel N, Weijer VCR, Decroix L, Bons J, van Loon LJC, van Dijk JW. Jumping exercise combined with collagen supplementation preserves bone mineral density in elite cyclists. International Journal of Sport Nutrition and Exercise Metabolism, 2024;34(1):38–47. doi:10.1123/ijsnem.2023-0080
• Brooke-Wavell K, Skelton DA, Barker KL, Clark EM, De Biase S, Arnold S, et al. Strong, steady and straight: UK consensus statement on physical activity and exercise for osteoporosis. British Journal of Sports Medicine, 2022;56(15):837–846. doi:10.1136/bjsports-2021-104634
• Mountjoy M, Ackerman KE, Bailey DM, Burke LM, Constantini N, Hackney AC, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 2023;57(17):1073–1097. doi:10.1136/bjsports-2023-106994