Cycling is an awesome activity and I am of course biased. The places it takes us, how it transforms our physical and mental fitness and wellbeing, whatever your preference from being competitive to riding for the simple pleasure of getting out or the daily commute. Cycling has many well documented positive attributes, but it is a non-weight bearing activity (NWB), which does have its downside, it can negatively affect bone mineral density (BMD).
BMD is essential for good bone health, keeping them strong and avoiding conditions such as osteopenia and osteoporosis later in life. It is built up over the first 3 decades of life and we can ‘bank’ bone mineral density depending on diet and weight bearing (WB) activities, with density typically peaking around the age of 35. Good nutrition is one of the key factors in generating bone density (calcium though green leafy vegetables, tofu, fish, vitamins such as vitamins D and K and potassium being the main ones), but the most significant way to increase and/or maintain BMD is WB activities, such as running. Genetic predisposition, endocrine and environmental factors also play determining roles in bone health and maintenance throughout life .
WB activities are those which involve impact and strain through the body, of which cycling is not included as the body is supported. In one study, it suggested that cycling is associated with lower BMD than that of the control participants , especially amongst road cyclists and the pro/elite population who will generally take the weight off their feet through sitting or lying down to recover as best as possible. (obviously doesn’t apply to those who have busy work and family lives!). Lower BMD is observed in key areas such as the lumbar spine and the femoral head, but this has been found to be less so in mountain bikers, but the research didn’t specify whether this related to hardtail or full suspension riders. One study even concluded that 2 thirds of professional and master amateur road cycles could be classified as osteopenic. 
From a young age, we develop BMD for life, being active across a variety of sports which involve impact with the ground, such as running and jumping, putting load and strain through the body, developing all aspects of general physical health. Learning to ride a bike is an essential and fun life skill of course, it’s when we decide that it’s our preferred sport and dedicate more time to it that we need to think about cross training, adding another activity that involves impact forces to offset the NWB aspect of cycling, to help maintain and build BMD. If ultra cycling is your thing, then adding in a WB activity should be a key component in the off season and/or regularly throughout the year.
WB activities aren't just about running, but can be anything that increases the load through the body beyond a habitual level. And it should be dynamic, not static, and the magnitude and rate of the stimuli should be high . If walking is not a regular activity, it could be considered relevant, but for many it is habitual and won’t be a high enough load to increase BMD, although it may be enough to maintain levels , but if the shoes have a highly cushioned sole that absorbs impact, this could negate any positive effect.
Running is an ideal WB activity to build into an off season/winter period, but if you are new to running, it is essential to build up SLOWLY, especially if older as age does play its part in our body's adaptation to new activity. You don’t have to turn into an ultra runner to reap the positive effects, as it is suggested that even short (and regular) runs are beneficial, but with ADEQUATE recovery time in between to allow the adaptations to bone, ligaments, tendons and muscle to take place, i.e full recovery before the next run. This is key to avoiding injury.
How long should I leave between running sessions is a common question. The recovery period will vary for everyone. If your achilles, joints and/or muscles are still feeling tired/sore after 72 hours don't go and do another run because the training programme says so. Listening to your body is a sound marker. The more adapted your body to the load of running the less time you'll need between run sessions. For those starting out on a running programme, less is more. As an example, the first couple of weeks could be 2 sessions of run/walk; 5 minutes walk, 2 minutes run repeated 4-5x. The following couple of weeks, increase the run time to 3minutes for one session, then both sessions for example. Progression could be to gradually decrease the walk time until you can continuously run without any issues such as achilles stiffness/pain, then gradually increase the run time of one of the sessions initially and so on.
Secondary to increasing BMD, WB activities such as running are beneficial for our joints too. As well as improving blood flow and synovial fluid circulation, the mechanical stresses through joints are essential for the maintenance of the morphological and functional integrity of articular cartilage . Even for the older long distance runner, they are no more susceptible to degenerative disease such as osteoarthritis than non runners  and Ponzio et al found that the arthritis rate of active marathon runners was below that of the general (US) population . Good news for those concerned about the possible negative effects on the knee joint.
Not all of us are able to run due to the high impact forces, whether it’s due to predisposing joint issues, anatomical variations or other factors, so an activity such as weight training could also be considered a significant enough stimulus as it generates forces from skeletal muscle contractions. Advice varies for weight training, b
ut I tend to advocate heavier weight, lower reps such as 6-8 reps with 3-5 sets depending on how adapted you are to strength training (or building up to that if new to it). There’s nothing wrong with 10 or 12reps, the main aspect is that the last couple of reps are hard to generate the desired stresses for hypertrophy.
Cycling has always been my passion, but I have always run a little too, especially in the winter months, leaving me feeling more prepared for some longer km on the bike once Spring comes around. This may be a combination of the positive effects of the WB activity, the different physical and mental stimulus as well as an activity that gets me out of that forward flexed, static bike posture that I spend hours in. Included in the winter programme is strength training too, for its specific benefits, but that is a whole other article.
Running for the cyclist does have significant benefits, especially for the long term health of our skeleton, but too much too soon will be counterproductive. It's a great way too to get a good workout with
in a short period if the weather is consistently bad. Plus no bike to clean! If you are keen on getting into running, start out super slowly, listen to your body as it’s about your body adapting to the ground reaction forces rather than a cardiovascular workout in those first few weeks. If you are unsure about anything, seek professional medical advice and/or advice from a coach.
1. Olmedillas, H., González-Agüero, A., Moreno, L.A. et al. Cycling and bone health: a systematic review. BMC Med 10, 168 (2012). https://doi.org/10.1186/1741-7015-10-168
2. Morseth, B., Emaus, N., & Jørgensen, L. (2011). Physical activity and bone: The importance of the various mechanical stimuli for bone mineral density. A review. Norsk Epidemiologi, 20(2). https://doi.org/10.5324/nje.v20i2.1338
3. JeanMedelli, JosephLounana, Jean-JacquesMenuet, MohamadShabani, ZaidaCordero-MacIntyre. Is Osteopenia a Health Risk in Professional Cyclists? Journal of Clinical Densitometry Volume 12, Issue 1, January–March 2009, Pages 28-34
4. Eliza F. Chakravarty, Helen B. Hubert, Vijaya B. Lingala, Ernesto Zatarain, James F. Fries, Long Distance Running and Knee Osteoarthritis: A Prospective Study,
American Journal of Preventive Medicine, Volume 35, Issue 2, 2008, Pages 133-138
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8. Benedetti, Maria Grazia et al. “The Effectiveness of Physical Exercise on Bone Density in Osteoporotic Patients.” BioMed research international vol. 2018 4840531. 23 Dec. 2018, doi:10.1155/2018/4840531
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