P&P #57: Osteoporosis.

1. From Dr J Wilmore:
   
   Mel, see Figure 19.9, page 460 of Physiology of Sport and Exercise (Wilmore and Costill) for help on the issue of women runners. It is only those runners who are amenorrheic who have bone mineral loss, and this is associated with decreased estrogen concentrations. We provide more of an explanation in the body of the text if you want more detail. Concerning swimmers, the loading forces are much less with swimming, thus there is not the stimulus for bone development to the same extent, although cross-sectional studies do show swimmers to have higher bone densities than age-matched untrained controls.
   
   MC Siff comments:
   
   I should also have requested respondents to this P&P to discuss separately the issue of compromised bone density among male and female subjects participating in different activities.
   
   I am also hoping to stimulate some users to compare the longitudinal compressive forces produced by load bearing and those produced by intense muscle contraction. This would then lead them to examine the relationship between bone density and muscle tension versus the relationship between bone density and gravitational loading (then, obviously drawing on that body of information derived from studies of astronauts and cosmonauts). All to often swimming is automatically regarded as an activity that cannot add to or maintain bone mineralisation because of the bouyancy effects of water (or 'absence of gravitational loading'). However, during the sprints or sprint phases of swimming, the level of muscle tension is high, so it would be interesting to compare the bone densities of elite sprint swimmers and recreational distance paddlers (and a cohort of 'sedentary' norms).
   
   
2. From Paula Papanek ppapanek@post.its.mcw.edu
   
   I alway read and discuss you puzzles with my students, and often have used them to get them going off on tangents. Thank you for your committment to learning. Regarding female runners and osteoporosis. Much information has been omitted from this presentation. For example, don't appear undernourished, is probably incorrect. When one calculates the energy balance of most of these women, they are often not in balance, or at least, ossilate in and out of energy balance, that is a negative or caloric deficit for their output. This negative balance, along with the repetitive high intensity of training increases cortisol release which breaks down skeletal muscle and facilitates osteopenia. In addition, these athletes are not eumenorrheic, that is to say, many do not have regular menstual cycles. While the definitions of primary and secondary amenorrhea and oligomenorrhea are strictly endocrinologically based, the important aspect for consideration is the low levels of circulating estrogen. Estrogen is critical not only to bone deposition during menarche, but in sustaining bone density during adult life. The interaction between estrogen and weight bearing exercise is important, because many women athletes will face the reality of their past soon. As Dr. Brinkwater is demonstrating, we have young women with very old bones. Gymnasts that are amenorrheic appear to have greater bone density than runners. Both groups have lower density than oligo- or eumenorrheic controls. This suggests that while load is important as a stimulus for bonde growth, different loads act differently. The mechanical force generated by a gymnast while performing floor exercises etc are greater than sustained running. Most importantly, we must begin to ask our athletes, when did you start menstrating, and how regular are your periods. While most coaches, ATC don't ask, the evidence is compelling that my generation of women athletes, are in for a disappointing future in terms of bone health, and clinically, we are preparing for them.
   
   M C Siff comments:
   
   *** Many thanks for your response. Your comments are all appropriate and you identified items that were omitted from the original posting. However, I should have added that male and female cases should be discussed separately.
   
   I could also have asked for comparisons between female runners and female weightlifters and the same for male cohorts.
   
   Would one still conclude that impoverished nutrition or regular negative energy balance are still the major causes of lowered bone density?
   
   What about the importance of the level of muscle tension produced during any activity and the effect of impact loading on the body? These and a few other questions from the previous posting still need analysis.
   
   
3. From DANIEL A SHAYE-PICKELL
   
   Dr. Mel Siff brings up some interesting questions, questions which I hope this discussion group can help solve. I lack the time or prior knowledge to cite literature in specific, but let me take a stab (and, should I fall on my face, let me learn from the experience!). Dr. Siff writes, "several studies have shown an increased incidence of osteoporosis or reduced bone density in distance athletes. Yet, all of the subjects are not undernourished or deficient in calcium intake." Do these studies show a threshold effect for the exercise-induced osteoporosis; that is, might there be a positive effect (long-term) for certain exercise intensities, but diminishing returns beyond that point?
   
   This would seem consistent with almost every "eustress" known. Exercise places tremendous physiological demands upon the body, and it does not seem unreasonable to me that the body's store of calcium, the bones, releases Ca to meet the demand. In fact, osteoclasis and osteoblastic activity are constant processes, one dominating the other based upon changing systemic demands. Perhaps certain levels of exercise turn on osteoclasis to the point that it exceeds net osteoblastic activity, to the point that the deficit is not made up even during the recovery period between exercise bouts. "In the case of swimmers, is the reported lower bone density also not contradictory? One must remember that bone is not loaded only under weight-bearing conditions but also under conditions where the bones are longitudinally stressed by increased tension in the muscles (actually the tendons) which attach to the bones. Among serious swimmers the muscle tension generated against water resistance is very great and the compressive component of this force along the bones should serve to stimulate mineralisation." It would seem so. I do not have a clever answer for this one, unless the mechanism be the same as referenced above... (again, I'd like to know what the threshold is for this effect).
   
   
4. From Daniel A. Shaye-Pickell, EMT, D.C. (8/96)
   
   By the way, what do the members of this b.b. think about, "Off the cuff" responses such as this one? Ideally, I'd be able to cite references for my theories (or do a MedLine search if I lacked prior knowledge), but time and my prior knowledge of this topic have limits. I believe that "musings" such as this may be of value. Feedback? -
   
   M C Siff comments:
   
   This is precisely one of the issues which I hoped which emerge from the original P&P, namely the possible existence of a training threshold effect or an optimal loading effect for a given individual at a given stage of training. The positive effects of training are solidified largely during the restoration period after exercise sessions.
   
   It is another possibility that inadequate formal attention is paid to adequate post-exercise restoration and nutrition by distance (LSD) athletes. In this respect, we can examine decreases in bone density along with other indicators of deterioration in terms of bioenergetic compromise. Here inadequate nutritional intake would share common ground with energy and protein deficiencies caused by exercise. Thus, one would not examine problems in terms of isolated causes, but as interrelated factors in an overall thermodynamic system.
   
   The importance of the 'after-effects' phenomenon, the use of the 'fitness-fatigue' model rather than the Selye (General Adaptation Syndrome) model and loading specific adaptation is a central theme in Russian research and has a direct bearing on the problem. We (Siff & Verkhoshansky discuss this issue in our text 'Supertraining', as does Zatsiorski in his book 'Science and Practice of Strength Training). The issue of adaptation to environmental stimuli needs to assume a role of greater importance in sports science. A great deal of apparently obscure work now being done on cellular mechanics and metabolism might well prove to answer some of the remaining questions in sport specific adaptation.
   
   
5. From Moira Petit, graduate student, UBC - dept. of Human Kinetics
   
   Mel, see Figure 19.9, page 460 of Physiology of Sport and Exercise (Wilmore and Costill) for help on the issue of women runners. It is only those runners who are amenorrheic who have bone mineral loss, and this is associated with decreased estrogen concentrations.
   
   M C Siff comments:
   
   Acutally, Dr. Prior has clearly shown that women may be menstruating regularly, but be anovulatory/have shortend luteal phase. In her article in the New Eng. J (1990) (sorry, I don't have the exact reference right now.. but would be happy to post it later) - she showed that low progesterone values associated with anovulation were related to loss of bone density in Marathon training, noramlly training, and sedentary controls. In other words, it wasn't training, but the anovulation/decrease in progesterone that led to bone loss - in women who were previously ovulatory.
   
   
6. From frank (fhd@interport.net)
   
   Dr M. C. Siff sez: "The relationship between bone disorder or damage such as osteoporosis and type of exercise or the lack of exercise might not be asunequivocal as some may believe."
   
   I'll take a small stab at this one ... Yet several studies have shown an increased incidence of osteoporosis or reduced bone density in distance athletes. Yet, all of the subjects are not undernourished or deficient in calcium intake. Does this not appear to contradict the earlier-mentioned theories? After all, the mineralisation of bone and increase in bone density appears to be associated with adequate compressive stress imposed by strenuous load-bearing activities. Force plate analysis shows that the impact loading during all forms of running (even long slow distance) can be many times that of one's bodyweight. Surely the cyclical imposition of this impact loading should increase bone density rather than decrease it - if such is the implication. Undernourished in what sense, compared to what baseline? Perhaps one factor which is being overlooked is protein catabolism -- a potentially large factor in endurance athletes. Additionally, distance runners, in particular because their skeletal system is subject to so much stress, may well require more calcium for use in repairing microfractures caused by the extreme stress.
   
   Comments from Dr. Siff on this particular item is unavailable.