High Intensity Training (HIT) is progressive resistance exercise performed with high level of effort. High Density Training (HDT) is progressive resistance exercise performed with a high work to rest ratio. Although it is possible to perform HIT without performing HDT by allowing a long rest between exercises, most HIT methods are HDT and are performed with little to no rest in between. Recently some trainers have been using the term in an attempt to differentiate themselves or sell programs, however HDT is nothing new and neither are these programs. Nautilus inventor Arthur Jones was recommending moving between exercises as quickly as possible back in the 1970’s and most HIT methods which evolved from Arthur Jones’ Nautilus training principles still involve the “rush factor.”
There are several benefits to moving quickly between exercises. Doing so significantly increases the demands on the cardiovascular system and the conditioning effect of a workout, as well as the metabolic demand on muscle groups targeted by two or more consecutive exercises. Due to cumulative systemic and local muscular fatigue rushing between exercises reduces the resistance required for subsequent exercises resulting in progressively deeper inroading and reduced stress on joints and connective tissue. Most obviously, rushing between exercises makes it possible to complete a workout very quickly making it a more viable way to train for people with tight schedules.
Some people promoting variations of HDT recommend performing repetitions more quickly for the sake of performing a higher density of mechanical work per time. This is not necessary to achieve the aforementioned benefits however, and as repetition speed increases so does the difficulty in maintaining strict form and the risk of injury. Performing repetitions slowly is both safer and more effective. The time you spend under load and the tension and metabolic stress on the target muscles are what matters, not how many times you make a weight go up and down.
The easiest way to move quickly between exercises is using selectorized machines like those made by Nautilus or MedX because it takes very little time to adjust settings and move the selector pin up or down the weight stack. Selectorized dumbbells are effective for this purpose as well. The same can be done with free weights if you have enough barbells and/or dumbbell handles and weight plates to load up all of your exercises ahead of time, but this would be impractical in most gyms and is usually only an option for people who train at home. The best way to accomplish this if you work out at a gym using either free weights or plate-loaded machines is to have a workout partner load the weight plates one exercise ahead of you and reserve the bar or machine then unload when you complete each exercise (if you are using a moderately slow repetition cadence and moderate rep range this gives them plenty of time). Another option is to perform bodyweight exercises, since there is usually little or no equipment to set up, and if you know how to perform bodyweight exercises correctly you can make them as easy or hard as necessary for your current level of strength.
As a general rule, if you want the greatest overall improvements in functional ability and health you should move slowly during exercises and quickly between them, not the other way around. HDT programs are nothing new, though. HIT has already incorporated this for decades.
2. Maisch B, Baum E, Grimm W. Die Auswirkungen dynamischen Krafttrainings nach dem Nautilus-Prinzip auf kardiozirkulatorische Parameter und Ausdauerleistungsfähigkeit (The effects of resistance training according to the Nautilus principles on cardiocirculatory parameters and endurance). Angenommen vom Fachbereich Humanmedizin der Philipps-Universität Marburg am 11. Dezember 2003