Thursday, August 19, 2010

"Successful aging" and changes in functional threshold power

by Andrew R. Coggan, Ph.D.

"Successful aging" has been defined by gerontologists as "multidimensional, encompassing the avoidance of disease and disability, the maintenance of high physical and cognitive function, and sustained engagement in social and productive activities" (1). Successful aging is therefore considered the antithesis of "usual aging", in which extrinsic factors such as habitual diet, level of physical activity, other personal health habits, and psychosocial factors magnify the effects of aging per se, contributing to the development of disability/disease and declines in physical, cognitide, and social functioning with the passage of time. In this context, Carl Groves' recent performances at master nationals as described in Hunter's post here:

strikes me as a superb example of successful aging, at least from the perspective of physical function. The fact that Carl was one of the first cyclists I met when I started riding and racing back in the mid-1970s makes his story especially inspirational to me.

In thinking about such issues, though, I began to wonder about the extent to which his high level of performance could be ascribed to minimizing the reduction in physiological characteristics (such as VO2max) that occur with aging, versus simply starting from a much higher-than-average level when he was younger. In other words, is he so fast (powerful) at age 82 because he hasn't slowed down as much as his peers, or has he always just been really, really fast (powerful)?

The question posed above obviously can't be answered with any certainty, since there is no way of knowing what Carl's functional threshold power actually was when he was younger. It is, however, possible to make a reasonable approximation, at least if you are willing to make the following assumptions with respect to the effects of aging:

1) regardless of training status, VO2max declines at a rate of 0.5 mL/min/kg/y starting at age 30;
2) lactate threshold does not change relative to VO2max;
3) gross efficiency remains constant at 23%; and
4) consumption of 1 mL of O2 yields 20.9 J of energy at the cellular level.

In the interests of space, I won't go into any detail regarding the basis for these assumptions, other than to emphasize that they are generally well-supported by the scientific literature. The one exception to this claim might be assumption #1 above, as some studies have suggested that training may slow the rate of decline in VO2max with age. Other studies, however, have not supported this conclusion, and if anything assumption #1 is conservative when extrapolating out beyond the 7th or 8th decade of life. Assumptions #2 and #3 are also conservative in the present context (since if anything both relative lactate threshold and efficiency seem to increase with age), thus tending to counter any error introduced by assumption #1.

Combining the above assumptions, the prediction would be that with aging (and assuming no significant changes in body mass over time), functional threshold power should decrease at a rate of 0.04 W/kg/y. If you then apply that rate-of-change to estimate Carl's functional threshold power at, say, age 40 the answer you derive is 3.83 W/kg + (42 y x 0.04 W/kg/y) = 5.51 W/kg. That is certainly a very high value, but clearly not unbelievable, and in fact is consistent with his performance (e.g., 2nd in the Indiana state championships, 13th at nationals) when he raced in the Amateur Bicycle League of America's (as USA Cycling used to be know) 40+ 'Veteran' class back in the 1970s.

As indicated above, probably the most questionable assumption I have made in performing this back-of-the-envelope analysis is that VO2max declines linearly at fixed rate throughout adulthood. In fact, based on both direct laboratory-based measurements as well as world record performances in most, if not all, endurance sports, it appears that the rate of decline in VO2max may actually acclerate as we go from being among the "young old" to being among the "older old" and "oldest old". This is why assuming a fixed rate of decline of 0.5 mL/min/kg/y as I have done can be considered a conservative assumption, as mentioned previously. Thus, my explanation for Carl's impressive performance ability at age 82, not only relative to others his age but even relative to many younger riders, is not that he was a physiological outlier when he was younger or even that he has managed to avoid the usual age-related decrement in VO2max and hence in sustainable power output. Rather, it appears to me that where he stands out is in the fact that he seems to still be on the linear portion of the curve relating VO2max to age, i.e., he appears to me to be biologically younger than suggested by his chronological years.

While Carl ascribes his succesful aging in terms of his cycling ability as being due to his lifelong saxophone playing, I believe it probably has more to due with his genes, as evidenced by his centarian mother. In any case, however, I do know this: I can only hope to be able to ride like Carl when I am his age!


1. Rowe JW, Kahn RL. Successful aging. Gerontologist. 1997; 37:433-440.

1 comment:

  1. In a classic case of arriving in the same place from a different direction, 4 years later, I was similarly trying to estimate the effect of ageing on FTP. I took the Veteran Time Trial Association Standards Tables for 40km and assumed that the associated power with those performances represented FTP. The result ? Average 0.04w/kg/yr after age 40. Exactly the same as you. However my results were not linear. The drop off was 0.03w/kg/yr until around 65 and then accelerating from there. That also seems logical to me.


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