Weight Training for Bone Health: Necessary or not?

In the past month or two I have seen a handful of articles written in cycling publications and coaches in the cycling community advocating the use of strength training in the “off season” (off season is a very poor choice of words, you’re either getting better or you’re not, I will use non competitive season hereafter) to combat bone loss. While there is not a body of evidence to suggest that strength training can improve endurance performance, it continues to be debated by cyclists, coaches and physiologists as to whether there is any cross over benefit. In my experience and through the research I have done I feel like the effects of weight training are very individual and must be considered on a case by case basis contingent upon each athletes goals, time commitments, pre-existing conditions, injury history, athletic development and extenuating factors. Additionally many reports suggest that low bone mass density (BMD) is a cause for a greater increase in fractures among cyclists, however this may not all together be true.

The goal of this post is not to go round and round on weight training and performance for cyclists, that’s a detailed discussion you should have with your coach or consulting physiologist/doctor, this post has a more specific goal.  With that we would like to analytically address the concept that cyclists should weight train during their non competitive season in order to improve bone density or attenuate bone loss. The reason this is important is that it must be weighed by the athlete/coach if time away from sport specific training is the most beneficial use of training time and if weight training is being done for the right reasons.

I am fortunate to coach one of the leading figures in bone health research, Dr. Gregorio Riera. Dr. Riera is not only an expert in his field but he is also a competitive cyclist. With that I asked Dr. Riera about some of the literature out there and how I seemed to be finding equivocal information at best and conflicting evidence at worst. What is really going on and what do we really know about bone health as it pertains to cyclist. Are cyclist more prone to fractures due to low BMD and poor bone health? Should cyclist weight train? Should they supplement with calcium? Should they even be concerned about it at all?  Below is a brief overview and review of the literature on bone health by Dr. Riera:

Low bone density in cyclists. Do we know the reality?
Gregorio Riera-Espinoza MD

Low bone density is a well known risk factor for fractures and indeed, the diagnosis of osteoporosis is based, most of the times, in Bone Mineral Density (BMD) measurements. In recent years BMD has been shown to be low in cyclists who train more than 10 hour/week for long periods of time, usually more than 8 years. Often cyclists are young and do not have osteoporosis, but are at high risk of traumatic fractures, so the point has been raised about two scenarios: Is low BMD a factor that increases the risk of traumatic fractures in cyclist? And second. Are cyclists at high risk of developing osteoporosis in the future? Both arguments deserve serious consideration.

The data, however, is conflicting. There are many trials showing low bone mass in elite or master cyclists at different ages (1-8), bone mass is measured as Bone Mineral Content (BCM) or Bone Mineral Density (BMD) at the whole body, spine, hip, legs or arms. In these studies BMD is decreased by 3-10% in cyclist compared to control subjects. If we translate this decrement in units of T-score [T-Score is the number of standard deviations above or below the mean for a 30yr old patient of the same sex and ethnicity], as WHO recommend, we end up with the possibility that a cyclist may have a T-score of -1.1 to -1.5, and this figure correspond to the diagnosis of Osteopenia, which is a range of bone loss previous to the diagnosis of Osteoporosis. WHO classification of bone loss include 4 categories: Normal: T-score between +1 and -1 (approximately no more than 10% of bone loss), Osteopenia: T-score between -1 and -2.5 (approximately between 10 and 25% of bone loss), Osteoporosis: T-score lower than -2.5 (approximately more than 25% of bone loss) and Establish Osteoporosis: if the patient already has a fracture. 

Most of the literature comes from cross-sectional trials, but there is one longitudinal study done in competitive male cyclist evaluated during one year (9). This report shows a decrease in total T-score of -1.5 in total hip and -0.5 in femoral neck, but not at the spine. Also calcium loss in the sweat was 136 mg after two hour of high intensity training. However, calcium supplementation did not avoid bone loss. 

Bone adapts to mechanical stimuli, bone strains of high magnitude and rate have the greatest osteogenic effects. High-impact activities like jumping and running induce loads that are multiples of body weight, whereas sports such as swimming and cycling, in which the body is partially supported, may generate smaller loads on the skeleton and the consequences may be less stimulus of the “mechanostat” and bone loss.

On the other hand, we have several trials where the decreased in bone mass could not be demonstrated in males, including elite athletes or female cyclist 18-32yrs  (10-14), using the same densitometry techniques. Very recent information using pQCT (Peripheral Quantitative Compute Tomography), a more precise technique to estimate bone structure, measured radius and tibia epiphyseal and shaft BMD and BMC, cross-sectional area along with shaft polar moment of resistance (RPol) and endocortical and/periosteal circumferences. These last two, are measurements of real bone strength, instead of just BMD, a component of bone strength. In this study cyclists tested at the Master Track Championship in Manchester UK, classified as sprint cyclists, distance cyclists and controls showed that cyclists have larger bone shaft and bone strength surrogates; the difference in diaphyseal BMC, area and RPol compared with controls were 10% or more in the tibia and 8% or more in the radius. Sprinters had the greatest bone strength surrogates in both the radius and the tibia, followed by distant cyclist and controls. The authors conclude that sprint and distance cyclists have greater tibia and radius bone strength surrogates than non cyclist controls (15). Another significant finding of this trial is that bone adapt without the action of impact forces.

Fracture incidence among cyclists is not known. Cycling is not different from other sports in causing traumatic fractures. Data from Australia showed that out of all sport injuries leading to fractures in adults (in % of number of injuries) martial arts, cycling, Australian football, soccer, rugby, cricket, basketball and dancing was between 17 and  25% for each sport (16). To our knowledge there is no report regarding cycling as a risk fracture for future osteoporotic fractures.

Some consideration should be done regarding low bone mass in cyclists:

1. Most trials use the term Osteopenia or Osteoporosis in young cyclist, but this is not correct. The WHO classification of bone loss applies only to Caucasian  postmenopausal women and not to young population. Recent position paper by the ISCD (International Society of Clinical Densitometry) states that the term osteopenia or osteoporosis should not be use in young subjects and “Low Bone Mass” in comparison to same age and sex must be used whenever low BMD is found. All studies in cyclists include young subjects and most of the times the peak bone mass has not yet being achieved.
2. There are no studies that correlate bone mass loss in cycling and risk of fracture, therefore the meaning of the small decrease in bone mass reported in many trials has no clear significance at this time, in terms of real risk of fractures
3. More specific techniques of estimation of bone strength like pQCT does not seem to support the fact of bone loss in cyclist
4. It seems like calcium supplementation does not prevent bone loss, but this statement is far from clear at the present time.
5. The final answers to the questions we ask early in this review can’t be found at the present time. Measuring Bone Mineral Density to elite cyclists looks prudent according to many published reports of low bone mass in such athletes. However, there are no approved treatment guidelines by any medical organization or association to use in this disorder, specifically related to cycling. Calcium supplementation in the order of 1500 mg day seems reasonably due to excessive calcium losses by sweat

The above review illustrates some key points that are generally not reported. We now see that indeed there is not data to support an increase in fractures due to low BMD in cyclist, additionally the bone strength of cyclists may not be as bad as once thought when more advanced measurement techniques are applied. This is certainly an area that warrants further discussion and research. BMD just as any other physiological marker should be monitored by your health care professional, but I’m not convinced that those singing the praises of weight training for bone health are fully justified. If bone loss is a concern a study out of Japan may have a better solution. Researchers there found that “men and especially women who engaged in <6,800 steps/day and <16 min/day of moderate-intensity physical activity were, respectively, 4.9–8.4 and 2.2–3.5 times more likely to sustain fractures than those participating in >8,200 steps/day and >25 min/day of activity.” (17) So maybe what cyclist should consider is simply taking the stairs instead of the elevator, parking a little farther away from the entrance of the restaurant and generally trying to walk a little more during there day. For many athletes that are already pressed for time to simply train taking a few extra steps per day vs. committing to a weight training routine might just be a step in a better direction.

Many thanks to Dr. Gregorio Riera for his generous time and insight on this subject.

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