Weight training as a form of Cardio
As a form of fitness training, strength training has many uses, one of them being the side benefit of cardiovascular fitness. Most people are so focused on the muscle building effect of strength training that they miss the other benefits.
Simply, anything that provides sufficient stimulus to the cardiovascular system and results in adaptations is cardio training. If load is sufficient those muscles involved in a compound require a significant amount of fuel in order to keep contracting and applying force. This fuel is supplied through all three energy pathways, being ATP/creatine phosphate anaerobic, the anaerobic lactate system and the aerobic energy system.
Resistance exercise is seldom used with the expressed purpose of enhancing cardiovascular function, but it does result in acute and chronic cardiovascular changes.
A recent study showed that cardiac output increased during mild dynamic exercise involving lifting and extending the leg (Elstad et al., 2009).
Throughout the leg exercise, heart rate was recorded and stroke volume was measured using Doppler ultrasound. In this study, heart rate increased by approximately 40%, and stroke volume decreased by about 5% . Thus, cardiac output increased by about 35%. Therefore, in this study, mild dynamic exercise with a light resistance caused a small increase in cardiac output resulting from a small decrease in stroke volume that was more than offset by the increase in heart rate.
Cardiac output responses to more intense resistance training have been reported by Lentini and colleagues (1993), who had healthy male subjects perform a double leg press to failure at 95% of their maximum dynamic strength. Stroke volume was determined using echocardiography and was reported preexercise, at the end of the lift phase, during the “lockout,” and during the lowering phase of the lift. Cardiac output increased significantly during the lifting phase and increased further during the lockout phase.
Revised guidelines from the American Heart Association suggest that resistance training may indeed be beneficial for those with known cardiovascular disease if contemporary prescriptive guidelines are employed with close supervision (Thompson et al., 2007). In a statement published by the American Heart Association (Braith and Stewart, 2006) regarding the use of resistance exercise in those with and without cardiovascular disease, the authors detail what is currently known about the safety of resistance exercise. They acknowledge that “excessive” blood pressure elevations have been documented with high-intensity resistance exercise (80-100% of 1RM performed to exhaustion), but note that such elevations are generally not a concern with low- to moderate-intensity resistance training performed with correct breathing technique. Furthermore, there is indirect evidence that resistance exercise results in a more favourable balance in myocardial oxygen supply and demand than aerobic exercise because of the lower heart rate and higher myocardial (diastolic) perfusion pressure (Braith and Stewart, 2006).
Further reading: Advanced Cardiovascular Exercise Physiology, by Denise L. Smith, PhD, and Bo Fernhall, PhD