If you want to be “fit”, know your goals (you must have goals) and know how your workouts will help (or not) you attain your goals. It is all about specificity.
It is important to realize that there are five distinct health-related components to physical fitness: cardiorespiratory endurance, muscle strength, muscle endurance, flexibility, and body composition. There is no single exercise program that will maximize all of these simultaneously. In my opinion, there is a trend in the fitness industry to sell body composition training on the myth that it will (significantly) affect cardiorespiratory endurance, muscle strength, muscle endurance. Lean with six-pack abs is sold as “fit”. If you buy this, you have to believe that the packaging is more important than the function.
The craze in fitness, today, is short, body-weight, “high-intensity” circuits (labeled as “HIIT”). These workouts are, indeed, calorie burners. More specifically, these appear to have a much greater and longer post-exercise energy expenditure (I can’t quite get the acronym to catch on for some reason) than traditional cardiorespiratory and muscle strength exercise. There may be some benefit in improved muscle endurance, but referring to this training as “strength training” is way off. This training, combined with a sensible, calorie deficient, diet, will promote fat loss. The loss of fat will cause the appearance of muscle hypertrophy, but the gains in muscle mass will be small at best. Likewise, the improvements in cardiorespiratory fitness (i.e., maximal oxygen consumption or VO2max) will be negligible. For a general fitness, these workouts are fine, but are probably best suited for alternative workout sessions.
Cardiorespiratory training must emphasize the overloading (i.e., doing a bit more than that to which the exerciser is accustomed) of the heart and circulatory system. In exercise physiology, it is well-established that cardiorespiratory function is affected by the ability to deliver oxygen to the working muscle (cardiac output = heart rate x stroke volume) and the ability to exchange gases (oxygen and carbon dioxide) and waste at the cellular level. The adaptable components to oxygen consumption are stroke volume (the amount of blood that is ejected from the heart with each beat) and arterio-venous oxygen difference (the amount of oxygen that can be extracted by the muscle as it passes through the tissue—this is largely impacted by the number of mitochondria in the muscle cell and the number of capillaries surrounding the muscle). I’ll avoid the extended exercise physiology lecture here and suffice it to say that to improve cardiac function, the heart has to be pushed to the intensities necessary to stimulate these adaptations.
Cardiorespiratory HIIT is quite different from muscle endurance HIIT. Exercise that is popularly called “Tabata” by trainers is not the IE1 protocol proposed by Dr. Izumi Tabata and colleagues in the 1996 paper. (Few of us can handle the IE1 protocol on a stationary cycle, let alone do bodyweight exercises to the prescribed intensity.) So, be sure that your HIIT matches your goals!
Likewise, the popular “Tabata” or “HIIT” training cannot be prescribed for muscle strength. Muscle strength, by definition, is the amount of force that can maximally be produced (measured as the one-repetition maximum, 1-RM). As such, strength is built with high-intensity and low repetitions (usually 1-5 repetitions). There is much to debate on the ideal repetitions, sets, volumes, and intensities for muscle strength training, but it is clear that high repetitions (greater than the 8-12 range) will not promote great gains in strength (there will, of course, be some residual gains as more weight is lifted in any repetition range).
The adaptions to exercise are specific to the imposed demands. If the training does not match the intended goals, well….
Give careful thought to what you do for exercise. There is no WOD (“workout of the day”) that is suitable for everyone. There is no WOD that can possibly meet the physiological demands to promote adaptation in all of the health-related components of fitness (and we haven’t even mentioned the motor skill-related components) simultaneously.
Determine your goals and plan your exercise accordingly. Don’t buy into the marketing myth that you can have it all in a matter of a few minutes a day. It takes careful planning and execution. It takes substantial effort.
Be your best today; be better tomorrow!
Carpe momento!