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Sunday, October 08, 2017

Is a sedentary life style and not resistance exercise a cause of concentric cardiac hypertrophy?

Following the 1975 echocardiographic study by Joel Morganroth of endurance athletes and resistance exercise athletes and several cross sectional studies that seemed to validate his work the  "Morganroth's  Hypothesis became  the standard exercise physiology party line.

The story goes like this:

Endurance exercise brings about a volume overload or a preload stimulus to the ventricle that lead to eccentric hypertrophy which is an increase in ventricular cavity size and only slight increase in wall thickness. Resistance exercise brings about a pressure overload or an afterload stimulus which leads to concentric hypertrophy in which there is little change in cavity size but thickening of the ventricular wall.,The 2 types can be defined more precisely  by the relative wall thickness (RWT) which is 2 x the posterior wall thickness dived by left ventricular diastolic diameter with the value greater than 0.42 indicating  concentric hypertrophy.

Skeptics have argued that echo studies have inherent  methodological errors  ranges too great   to separate groups whose absolute values are not that far apart and MR is a much more precise method and that cross-sectional studies have limited ability  to sort out group difference that  are due to training  from other causes of individual differences.So what did a longitudinal study with MR imaging show?

A 2011 MRI longitudinal study provided interesting data from which one might conclude that endurance exercise does bring about eccentric hypertrophy but resistance exercise does not increase wall thickness-at least not in the small group of resistance exercisers who worked out three times a week for six months.

Spence et al (2) from Australia did a MRI study on   a small number  of subjects with one  group undergoing endurance training and the other resistance training.

 While Spence's study  suggests that six months of   resistance exercise does not lead to concentric hypertrophy,data from the group  Southwestern Medical School indicate that a sedentary lifestyle can bring about concentric hypertrophy at least some of the time.

 Brinker et al (3) studied cardiac function and structure in 2900 subjects from the Cooper Center Longitudinal Study. They found that the low fit subjects ( basically those with a sedentary lifestyle) had a higher prevalence of concentric remodeling as well as diastolic dysfunction that the fitter subjects. There was a 40% prevalence of concentric hypertrophy in the lowest fit group versus less than 20 % in the most fit group. So it is not an all of none thing.

 The notion of volume overload exercise and pressure overload exercise may well be a oversimplification. A recent meta-analysis provided data to support the notion that there is some pressure overload in endurance exercise and there is apparently some volume overload in such resistance exercise. Further a number athletic endeavors are mixed, such as rowing and cycling. The rowers and cyclists had the greatest remodeling changes with both increased left ventricular end diastolic volume and wall thickness. 

 But it may also be the case  to be the case there there is "inactivity remodeling", here referring to a sedentary lifestyle The ventricles remodel  whether  you exercise or have a sedentary lifestyle., you likely get a eccentric remodeling or hypertrophy with  aerobic exercise and  at least in some people without it you get concentric remodeling or hypertrophy.Further, they suggest as have others that the latter may well be a precursor to heart failure and the former may help prevent it.

 1. Morganroth, Jet  al. Comparative left ventricular dimensions in trained athletes.Ann Int Med. 1975,82(4), 521-524
 2. Spence,A et al A prospective randomized longitudinal study of left ventricular adaption to endurance and resistance training in humans. J Phys 2011 589, 543
 3.Brinker, SK et al. Association of Cardiorespiratory Fitness with Left Ventricular Remodeling and diastolic dysfunction. JACC Heart Failure.Vol 2, no.3, 2014, p238

"Humans are pattern-seeking, story-telling animals and we are quite adept at telling stories about patterns,whether they exist or not" Michael Shermer.

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