HIT vs HIIT, Sprints vs Resistance Training: What’s the Difference?

Is there a physiological difference in response between sprinting all-out (on a bike, treadmill, rowing machine etc) until you are unable to maintain a peak cadence level versus performing a high effort resistance training (RT) exercise? Due to a perceived dichotomy between cardiovascular exercise and resistance training, this is not a question that has been significantly explored in the scientific literature. A recent research paper published in PeerJ, titled “Similar acute physiological responses from effort and duration matched leg press and recumbent cycling tasks” and authored by James Steele, Andrew Butler, Zoe Comerford, Jason Dyer, Nathan Lloyd, Joshua Ward, James Fisher, Paulo Gentil, Christopher Scott and Hayao Ozaki seeks to answer this question.

Why should you care?

If resistance training and CV exercise performed to a similar intensity of effort stimulate comparable physiological outcomes, there are implications for exercise programming. This applies whether you are a personal trainer working with clients or you are just training yourself.

For instance, if sprints can provide a hypertrophic stimulus similar to resistance training, instead of doing 2 full body RT workouts per week an athlete could do 1 full body RT routine and on the other day one upper body only RT workout combined with cycle ergometer sprints.

On the other hand, if resistance training can provide all the benefits typically associated with CV exercise and an individual has no desire to perform any other formal exercise than resistance training, they can feel free to only perform RT.

Essentially if we understand that sprints and high effort RT provide a similar stimulus then we may have a better understanding of how to schedule workouts for athletes. Individuals can also be liberated to choose an approach to exercise they enjoy the most: one in which they are most likely to initially engage in and to stick with.

What did the researchers compare?

The researchers took a group of 9 subjects and had them perform;

a) A leg press for 4 sets of 12 repetition maximum. The exercise was performed at a tempo of 2 seconds for the concentric stroke and 3 seconds for the eccentric stroke. Therefore, each set of the leg press lasted 60 seconds.

b) 4 sprints of 60 seconds each on a recumbent cycle ergometer. The resistance level used enabled the subject to maintain 80-100 rpm until the last 5-10 seconds of the bout.

Both protocols utilized a 4-minute rest between each 60 second work period.

Note that the RT sets were not specifically taken to failure (MMF), but rather to repetition maximum. Perceived effort feedback collected from the subjects during the research revealed that although perceived effort was very high, it was not maximal. There is therefore, perhaps potential for somewhat improved results from RT if the sets are taken to MMF.

What physiological responses did the researchers measure?

• Oxygen consumption- VO2, the amount of oxygen utilized during exercise. This was measured both during exercise and in the rest periods between sets/sprints.
• Respiratory exchange ratio- RER, the ratio between metabolically produced carbon dioxide (CO2) and oxygen (O2) used. This was also measured both during exercise and rest periods.
• Blood lactate- a measurement of lactic acid levels in the blood produced by anaerobic metabolism. This was measured at the end of each protocol.
• Energy expenditure- the number of calories used. This was estimated for both exercise and rest periods.
• Muscle swelling- the researchers used an ultrasound measurement of muscle thickness. Muscle thickness was measured before and after each protocol.
• Electromyography- EMG, a measurement of the electrical activity within muscle tissue. This was measured throughout the entire exercise periods.

We may expect to see:

The researchers suggest that if the physiological response to sprints and high effort RT is comparable we would expect to see similarities in:

• Levels of aerobic and anaerobic metabolism
• Working muscle oxygen utilisation (VO2)
• Lactate production
• Muscle swelling
• Electrical activity in muscle tissue.

What did the research find?

• VO2 responses were similar between protocols suggesting RT can improve cardiorespiratory fitness.
• Blood lactate response was similar, suggesting RT can stimulate improvements in blood lactate clearance.
• Aerobic, anaerobic, and total energy expenditures were similar, again pointing toward RT providing a stimulus that results in improvements to cardiorespiratory fitness that have traditionally been perceived as the preserve of “CV modes” of exercise.
• As both RT and sprints had similar total energy expenditures both have the potential to be similarly effective as part of a fat reduction programme.
• Motor unit recruitment and muscle swelling was similar between the protocols suggesting that sprints may provide a hypertrophic stimulus comparable to RT
• Overall it appears that sprints and high effort RT can provide similar physiological responses.

What’s the difference then?

We might well ask ourselves when does cardio become resistance training and when does resistance training become cardio? Is there any real difference? Physical activity and exercise are perhaps best thought of as existing on a continuum, one that could look like this:

Gentle walk < Brisk walk < Jog < Run < Sprint/ Resistance training to MMF

In certain muscle groups at least, sprinting can likely stimulate hypertrophy and strength gains in much the same way as resistance training does. And high effort RT can stimulate cardiorespiratory improvements.

Think of this: any sprint distance between 400-800 meters has world class athletes utilizing their anaerobic and aerobic energy systems pretty much equally and maximally. How long does it take the world class athlete to cover those distances? Roughly speaking from 45 seconds to 100 seconds.

Those numbers are very familiar. In HIT RT most individuals perform exercises for somewhere between 45-100 seconds. Much like the 400-800 meter sprinter, during HIT RT we are driving our aerobic and anaerobic energy processes maximally to cope with the metabolic demands of our resistance training protocol.

Note then that the 60 second work periods chosen by the researchers for this study represents a sweet spot for equal challenge to the aerobic and anaerobic energy systems. It makes sense that there would be little difference in the physiological responses, as the metabolic demands should be near identical.

General thoughts

The scope of this research was to specifically study acute responses to exercise, it would also be interesting in the future to see research that compares chronic or long-term adaptations to both sprints and high effort RT. The sample size for this study was quite small, consisting of only 9 males, it would be great to see similar research with a larger number of individuals, and indeed with females too.

The message that the authors of this research are getting out is that to get the best health and fitness results individuals should be encouraged to exercise first and foremost with a relatively high intensity of effort. Then personal preference and/or individual circumstances can drive the choice of exercise modality, which will likely help with both initial participation and with longer term adherence.