Cardio and The Heart: LISS vs. High Intensity Training


In several recent posts I have discussed the controversy over whether a significant amount of Low Intensity Steady State (LISS) cardio training is a good idea: here, here, and here. I concluded that LISS is beneficial and that the arguments that it causes muscle wasting are exaggerated. A combination of LISS cardio, strength training, and higher intensity cardio is ideal, in my opinion.

But there is another health aspect I have not covered: what is the effect of different types of training on our hearts? Changes in the heart due to exercise are referred to as cardiac remodelling. There are two main types: eccentric remodeling, where the chambers of the heart (especially the left ventricle, which pumps oxygenated blood out to the body) enlarge, and concentric remodeling, where the walls of the heart thicken. Eccentric is considered especially beneficial- an increase in the chamber size of the left ventricle increases the stroke volume of the heart’s pumping action. This makes the heart pump more per beat, and the heart rate to become lower, at rest and during activity, which is considered healthier.

A good overview of the longer term changes to the heart caused by different exercises is in [1]. The common rule of thumb among cardiologists that a “strength trained heart” undergoes concentric remodeling, while an “endurance trained heart” undergoes eccentric remodeling. This rule of thumb is a bit oversimplified, there are a lot of gray areas [2]. There is nothing wrong with some concentric remodeling, but in excess it can increase risk for adverse cardiac events [2]. But it might not be the best for our hearts to do only strength training and high intensity interval training, and omit a good dose of LISS, and miss out on healthy eccentric remodeling.


  1. Fulghum, K, and Hill, B, “Metabolic Mechanisms of Exercise-Induced Cardiac Remodeling”, Front. Cardiovasc. Med., 2018.
  2. Mihl, C, et al, “Cardiac remodelling: concentric versus eccentric hypertrophy in strength and endurance athletes”, Neth. Heart J., 2008.