Time is sought after when we need it, yet is often mismanaged. Time also happens to be the most cited reason against participating in deliberate exercise.
"I just don't have the time to workout."
Herein grows the counter-culture for 'time-sensitive workouts' where the emphasis is placed on shorter duration but higher intensity exercise as a means of 'reaping the benefits of physical activity within a manageable time frame'.
But can that '10 minute workout' actually be EQUALLY beneficial for you compared to a longer duration workout?
Is there an optimal amount of time that exercise should last in order to get the best results?
The current exercise recommendations from the World Health Organization (WHO) and the American College of Sports Medicine (ACSM) suggest at least:
150 minutes of moderate-intensity (40-60% of VO2max) physical activity every week*
OR 75 minutes of high intensity (60-85% of VO2max) physical activity every week*
*These are weekly averages, NOT daily estimates
[But how do you know what intensity you are exercising at? A good rule of thumb is to think of a 1-10 scale of difficulty, 10 being the most difficult/unable to complete. We tend to exercise easily around the 40-60% range (or a 4-6 on the 1-10 scale of difficulty), but start to struggle as it increases. Usually greater intensities (maybe an 8.5 up to a 10 on that 1-10 scale) are going to be extremely difficult or even unable to complete depending on the exercise/day/your mood/etc. *If you are able to hold a conversation during exercise, it's probably a lower intensity (40-60%) ]
These exercise duration guidelines can be broken up as needed, but often are recommended as:
30-60 mins/day up to 5 days/week for moderate intensity (roughly ~150 minutes/week)
OR 20-60 mins/day for 3 days/week for vigorous intensity (roughly ~75 minutes/week)
According to these guidelines, whether these recommendations are met with one bout per day (like a single workout of 30 minutes), or multiple shorter sessions (of at least 10 minutes each) throughout the day, are BOTH acceptable means of meeting the recommendations. Again, the emphasis here is largely placed on the TOTAL amount of time spent exercising (the overall trend of being physically active), and not necessarily on the specific amount at a given time, albeit 10 minutes is the shortest recommended duration.
When it comes to weight loss...
If the goal is to control for body weight, then 60 min/day for most days of the week is recommended by the Institute of Medicine. (Jakicic, et al. 2003) ["Most days of the week" would mean 4 or more, therefore 60 mins/day X 4 days/week= at least 240 minutes/week.] Again, it is implied that this could be cumulative throughout the day (like multiple 10 minute bouts) or one continuous 60 minute session. The general consensus behind these guidelines is that total energy expenditure, both throughout the day and throughout the week, are going to equate to overall physical activity levels and caloric deficit.
But is it really TIME spent exercising, or the AMOUNT of exercise that matters?
There are some older study findings to suggest that a greater amount (or volume) of exercise per week was associated with the greatest decrease in fat mass when diet was not altered. (Slentz, et al. 2004) In this study, participants followed an 8 month exercise regimen of either:
high intensity/high amount (about 204 minutes/week at 65-80% of max effort)
high intensity/low amount (127 minutes/week at 65-80%)
or moderate intensity/low amount (200 minutes/week at 40-55% maximum effort
*Take note that in this study, "amount" is defined as the total volume of work completed, and NOT total time spent working. The "high amount", or high volume, was equivalent to 20 miles/week, with the "low amount" equivalent to 12 miles/week. That being said, the 'low amount/moderate intensity' group will take longer to equal those 12 miles compared to the 'low amount/high intensity' group completing those 12 miles. Thus, the 'low amount/moderate intensity' groups ends up exercising for roughly the same amount of TIME as the 'high amount' group, but with differences in total work completed between the two groups.
The participants continued following their normal diets so there was no control over caloric intake which should imply that the observed changes in body weight and composition were due to caloric expenditure in the form of the exercise intervention, and NOT from a change in caloric intake. According to the study, the participants that exercised at high intensity for higher amounts (higher overall volume of work completed) exhibited the greatest amount of weight loss and fat loss while both of the lower volume groups had significant decreases in weight and fat mass compared to controls, but without any differences between the two low volume groups. (Slentz, et al. 2004) Translation: This means that the two groups that did LESS TOTAL WORK (compared to the high amount/high intensity group) still saw weight loss and fat loss, but were NOT otherwise different from each other (high intensity vs. moderate intensity). In this case, BOTH low volume groups still saw results compared to control as the sample participants were all inactive to begin with, so ANY increase in physical activity is going to warrant changes. However the fact that there was NO difference between the two low volume groups, but rather a significant difference in the high volume/high intensity group could imply that the total amount or volume of exercise or total capacity for caloric expenditure, is really the driving force for these decreases in weight and fat mass, compared to just total time spent exercising. *Again, the moderate intensity/low amount group spent roughly the SAME TOTAL TIME exercising as the high intensity/high amount group (both groups ~200 minutes/week), but where the differences lie in the volume of work completed i.e. get more 'bang for your buck'
And what happens when diet is also controlled for...
In another older study, a sample of sedentary overweight and obese women participated in a 12 month study consisting of exercise and diet. (Jakicic, et al. 2003) The women were randomly assigned to one of four different exercise conditions of either:
high intensity+long duration
high intensity+short duration
moderate intensity+short duration
moderate intensity+long duration
It is important to note that all women were considered sedentary at baseline and ALL women were instructed to follow a diet of 1200-1500 calories/day with dietary fat of 20-30% of total caloric intake. (Jakicic, et al. 2003) *Take note: this is a blanketed dietary plan that puts virtually ANY person, regardless of their size and caloric needs, in a caloric deficit.
In this study, the exercise prescribed was walking for at least 10 minutes at a time, at least 5 days/week where intensity was assessed via heart rate and rate of perceived exertion/RPE (how easy or hard the exercise feels). Unsurprisingly, all groups showed significant weight loss at 12 months from baseline, but there were NO significant differences between groups. (Jakicic, et al. 2003) This last point is important to note that despite differences in intensity and exercise duration, that ALL groups showed significant weight loss from the intervention of adding exercise (they were all previously sedentary) AND controlling for diet (they were all following an energy restricted low-fat diet). All groups also saw improvements in cardiorespiratory fitness at 6 months and 12 months from baseline, but with NO significant differences between groups. (Jakicic, et al. 2003) This again suggests that the addition of physical activity to a previously sedentary lifestyle is undoubtedly going to improve markers of fitness. There was however a significant increase in total weight lost for the group that totaled the highest amount of exercise of 200 minutes/week compared to 150 minutes/week or less (those that moved more lost 10% of body weight, compared to 8% weight loss in those that didn't move as much). (Jakicic, et al. 2003) This suggests that the more TOTAL movement (energy expenditure) throughout the week was associated with the greatest improvements in body composition.
So what makes HIIT different from traditional steady state exercise?
HIIT training (high intensity interval training) typically consists of short bouts of work interspersed with brief rest periods.
The work interval can last from 6 seconds long up to 4 minutes, and is high intensity effort (>85% VO2max, or the rough equivalent of something that feels like an 8.5 or higher on a scale of 1-10 for difficulty)
The rest interval can last between 10 seconds long up to 5 minutes long as is usually a low intensity aerobic rest at 20-40% VO2max or the equivalent of 2-4 on a scale of 1-10 difficulty.
A meta-analysis of the effects of HIIT training on cardiovascular health showed that HIIT training improved VO2max, decreased diastolic blood pressure, decreased fasting glucose, and lipogenesis (the formation of lipids/fat) compared to moderate-intensity continuous exercise. (Batacan, et al. 2017)
But when it comes to body composition...
In this meta-analysis, there were NO findings of effects of either short-term or long-term HIIT training on improving body composition and body fat percent in normal weight populations. (Batacan, et al. 2017) In overweight and obese populations, meta-analyses showed that short-term HIIT reduced waist circumference while long-term HIIT improved waist circumference and body fat percentage. (Batacan, et al. 2017) *Short-term HIIT is considered less than 12 months, long-term is considered greater than 12 months.
So can HIIT actually be EQUALLY as beneficial as continuous exercise, but in less time?
Another study looked at the potential effects of either HIIT versus moderate intensity continuous training (MCT) where a sample of inactive middle-aged women were randomly assigned to follow either:
HIIT training 3x/week for 12 weeks
MCT 3x/week for 12 weeks
control (maintained sedentary lifestyle)
The exercise programs consisted of indoor cycling for a total of ~50 minutes/day 3x/week for the 12 week program. (Connolly, et al. 2017) The MCT group would perform continuous cycling for 50 minutes. The HIIT group would perform a 5 minute warm up, and then cycle for 30 seconds at low intensity (30% of max effort), 20 seconds of moderate intensity (50-65% of max effort), and then 10 seconds of high intensity (>90% of max effort). (Connolly, et al. 2017) [30 seconds + 20 seconds + 10 seconds= 1 minute of varying intensity] This one minute of increasing intensity would repeat 5 times (for a total of 5 minutes) followed by a 2 minute rest, and this 5 minute block would repeat for 5 total sets. (Connolly, et al. 2017) The HIIT group would finish with a 5-10 minute cool down.
So it looked like this:
5 rounds:
5 sets of 1 min interval (30 sec, 20 sec, 10 sec)=5 minutes of varying intensity work
2 min rest between rounds
[This equates to 25 min total working time for the HIIT group workout, but 45-50 minutes of total time exercising when warm up, rest intervals, and cool down are added in to the total time spent at the gym.]
There was NO significant difference between the groups in mean power output or heart rate but both groups showed increases from baseline in peak power output and VO2peak compared to the control group.(Connolly, et al. 2017) There were NO significant differences between groups in body fat percent, BMI, or body composition, but the HIIT group did significantly decrease total body mass. (Connolly, et al. 2017) Systolic blood pressure was reduced in the MCT group, and both groups showed improvements in visual learning, memory, and verbal learning with no differences between groups on well-being and enjoyment of exercise. (Connolly, et al. 2017) *Essentially, both training methods showed similar effects in improving fitness, cognition, and metabolic health. Take note of the differences in TOTAL exercise time where the HIIT group would equate to 75 minutes of exercise/week, and the MCT group would equal 150 minutes exercise/week, yet BOTH groups are spending 50 minutes of their day performing their exercise i.e. STILL SPENDING THE SAME AMOUNT OF TIME AT THE GYM.
*Again: despite less working time with HIIT, the total time spent at the gym was the same (based on this study design) which dismantles the argument that it is a 'time-sensitive method of training'.
Another study compared HIIT (high intensity interval training) and moderate intensity/continuous training (MCT). In this study, participants performed 30 minutes of exercise where the HIIT group performed a 5 minute warm-up, 10 intervals of 1 minute high intensity (84-87%) work:1 minute rest (20 minutes total) followed by a 5 minute cool-down. The other group performed a 5 minute warm-up, 20 minutes of moderate intensity (55-59%) continuous exercise, and followed by a 5 minute cool-down. (Vella, et al. 2017) After 8 weeks of performing these 30 minute bouts of exercise 4x/week (120 minutes/week), exercise adherence and enjoyment were similar between both groups and there were NO significant differences in body weight or body composition for the duration of the study (which may indicate that 8 weeks was too short of a duration, or that the total time of 120 minutes/week was not enough for weight loss). (Vella, et al. 2017) The HIIT group did have a significant decrease in LDL cholesterol and increase in VO2 peak from baseline compared to the moderate-intensity continuous exercise group. (Vella, et al. 2017) This means that while this exercise prescription may not have been enough to elicit weight loss, it did show beneficial for improving cardiovascular fitness and reducing risk for cardiovascular complications.
*This could suggest that 30 minutes/day may be all that is needed to see improvements in cardiovascular fitness and health parameters.
**Also take note: when you hear "just 10 minutes a day of HIIT"...that means 10 working minutes + rest intervals, warm up, cool down, etc, NOT just 10 minutes total.
When it comes to cognitive improvements from a bout of exercise...
Study findings suggest that the strongest positive relationship between exercise and improved cognition is associated with an exercise bout that includes a 5 minute warm up, 20 minutes of moderate-intensity exercise, and a 5 minute cool down period (meaning 30 minutes in total) while shorter or longer duration exercise bouts were associated with less of a response. (Chang, et al. 2015) In this study, 'improved cognition' implied both increased arousal and improved scores on a cognitive task assessment. The primary finding from this study showed shorter response time with higher accuracy for a 20 minute moderate-intensity workout (~65% of maximal effort) compared to a 10 minute workout or a 45 minute workout. (Change, et al. 2015) These findings may suggest an optimal 'window of time' where 30 minutes of exercise may be the most beneficial amount of time for improvements in cognition and alertness.
Take-home message:
Exercise of at least 30 minutes/day can improve cognitive function, cardiovascular fitness, and health parameters.
Greater total volume of work (as a weekly average) may be needed to see weight loss and changes in body composition.
Diet and exercise will play a strong synergistic role in changing body composition.
HIIT and MCT show similar effects for body composition and cognitive health, with some differences in cardiovascular and metabolic improvements between the two.
HIIT really is not THAT time-saving, but rather finding exercise that you enjoy and will stick with is going to be the most important factor with long-term adherence and success.
References:
Batacan R, Duncan M, Dalbo V, et al. Effects of high-intensity interval training on cardiometabolic health: a systematic review and meta-analysis of intervention studies. British Journal of Sports Medicine. 2017; 51(6): 494-503. http://bjsm.bmj.com.proxy.lib.fsu.edu/content/51/6/494.long
Chang Y, Chu C, Wang C, et al. Dose-response relation between exercise duration and cognition. Medicine and Science in Sports and Exercise. 2015; 47(1): 159-165. https://insights-ovid-com.proxy.lib.fsu.edu/pubmed?pmid=24870572
Connolly L, Bailey S, Krustrup P, et al. Effects of self-paced interval and continuous training on health markers in women. European Journal of Applied Physiology. 2017; 117(11):2281-2293. https://link-springer-com.proxy.lib.fsu.edu/article/10.1007%2Fs00421-017-3715-9
Jakicic J, Marcus B, Gallagher K. Effect of Exercise Duration and Intensity on Weight Loss in Overweight, Sedentary Women. JAMA. 2003; 290(10):1323-1330. https://jamanetwork.com/journals/jama/fullarticle/197256
Slentz C, Duscha B, Johnson J. Effects of the Amount of Exercise on Body Weight, Body Composition, and Measures of Central Obesity. Archives of Internal Medicine. 2004; 164(1):31-39. https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/216495
Vella C, Taylor K, Drummer D. High-intensity interval and moderate-intensity continuous training elicit similar enjoyment and adherence levels in overweight and obese adults. European Journal of Sports Science. 2017; 17(9): 1203-1211. http://www.tandfonline.com.proxy.lib.fsu.edu/doi/full/10.1080/17461391.2017.1359679