Featured Post

Is the new professionalism and ACP's new ethics really just about following guidelines?

The Charter ( Medical Professionalism in the New Millennium.A Physician's Charter) did not deal with just the important relationship of ...

Tuesday, June 22, 2021

Octogenarians and exercise capacity

 The average 80 year old who is healthy has a maximal oxygen capacity of about 20 ml.kilo/min. This is sufficient exercise capacity to finish stage 1 of the Bruce treadmill protocol which requires a 02 uptake of about 17.5. A 02 max of 20 should allow an orthopedically competent  person to walk a mile in 16 minutes. 

The 02 max value of 17.5 ( or 5 Mets) has been quoted as being necessary to be able to handle independent living and a value of less than 7  (2 Mets)  has been considered  considered incompatible with life. (I have been unable to find a reference that confirms that value )

The stylized story of maximal 0xygen uptake (V02 max) and human aging is something like the following:

V02max, heart rate and fat free weight begin to decline around age 25. Multiple studies have demonstrated that the average per decade decline in V02 max is about 9 - 10% while some data suggest that with continuing physical activity the decline may be only 5 % per decade (1)

However, the rate of decline appears to greatly increase after age 65 or 70 as the   curve  becomes curvilinear

Trappe et al studied 55 former elite distance runners after a 22 year period. Their data confirm earlier studies indicating there is a 5-7% per decade  decrease in aerobic capacity even in highly trained athletes. They also found that the subset who did not exercise regularly had a greater percentage decrease in V02max.

Viewed from beneath  the apex there is a systolic counter clockwise rotation of the apex and a clockwise rotation of the base of the heart, likening to wringing out a wash cloth. During diastole there is an untwisting most  of which occurs during the isovolumic relaxation phase of the heart (IVRT).This untwisting represent elastic recoil which is said to be due to the release of restoring forces.Decrease in this suction generation is thought to paly a role in so called diastolic heart failure ., now referred to as heart failure with preserved ejection fraction (HFpEF)

 However, data from Ben Levine's group at the Institute for Exercise and Environmental Medicine in Dallas  indicate that while there is some preservation of left ventricular compliance in those with a history of lifelong exercise ( defined as 25  years or more)  an increase  in IVRT occurred in both  the exercisers  and in the sedentary group.So Levine's data indicate that 4-5 hours of aerobic exercise per week maintained over " a lifetime" will preserve to a significant degree left ventricular compliance but not the prolongation of LV relaxation which accompanies old age.

Tanaka and Seals (3)  in their review article challenge Trappe and other researchers who hold the generally accepted position that regular aerobic exercise will blunt the age related decrease in v02 max. Less controversially  they  suggest that the decline in V02 max is mostly likely due to an age related decline in stroke volume. If  V02  =SV x HR x A-V 02 difference and they claim that there is not a significant decrease in maximal HR  nor AV 02 difference with aging, then only suspect variable left is the stroke volume.

A decreased stroke volume with exercise ties in nicely with the observation that the left ventricular relaxation ( as measured by AVRT  which is the time between aortic valve closure and mitral valve opening) is increased even in highly trained older endurance athletes. With prolonged relaxation time there would be less time for ventricular filling with the increased heart rate associated with exercise , so there is  less LV filling with each cardiac cycle leading to less ability to increase stroke volume with exercise.Add to that the decreased compliance of the left ventricle that occurs with sedentary aging and we can understand at least some of why V02 max decreases with aging.

However, there is more at work with the decrease in exercise capacity related to aging tha nthe decrease in  V02 max.One interesting data point in that regard is the observation that Ed Whitlock marathon times decreased from age 70 to age 82 with there being no change in his measured V 02 max.

At age  70  Whitlock  ran a 2:54 marathon and at age 82 his marathon time decreased to3:41This is a change  from  6.62 minutes per mile to 8.4 minutes per mile or a change from  9 miles per hour to 7.11 miles per hour, a 20% decrease.  Yet during that same time period his measured maximal oxygen uptake was unchanged. We also know from  published interviews  that his training did not significantly diminish. So what was the cause(s) of his decreased running speed?

1)Pollack, ML et al Twenty-year follow-up of aerobic power and body composition of older track athletes

J of App Physio 82 (25) 1508

2) Trappe, SW Costill,DL et al Aging among elite distance runners: a 22 yr longitudinal study

J of App Physiol Vol 80 no 1 285 1996.

3) Tanaka,H Seals,DR Invited review. Dynamic exercise  performance in Masters athletes Insight into the effects of primary human aging of physiological functional capacity.  J of Appl Physiology 2003 vol 95 no 5 2152

No comments: