A recent study shows that people who use high-intensity interval training (HIIT) are far more likely to become injured than people who use less intense exercise and that the highest injury rate from interval training is in men at ages 20 to 39, the ages when they are at their highest potential to be at their best competitive level to become champion athletes (J Sports Medicine and Physical Fitness, Feb. 12, 2019).
Almost all competitive athletes use some form of interval training because shorter bursts of very intense exercise are far more effective than more casual exercise to make you stronger and have greater endurance. Intense interval training has also been shown to be more effective in maintaining fitness and preventing diseases such as heart attacks than casual exercise, because intense interval training strengthens the heart more, widens blood vessels more and increases maximum circulation (Cell Metabolism, Mar 7, 2017;25:581-592). Interval training also takes far less time than continuous training for these exercise benefits (J of Physiology, March 2010).
Most Non-Athletes Prefer Less Intensity
People who exercise just for fitness, weight control and health tend to prefer longer, more moderate-intensity, continuous exercise workouts that burn the same number of calories compared to short but very intense interval training (J Sport & Exercise Psychology, April 2016). Athletes need to use intense interval training to be competitive, but the average non-athlete may be happier in a less intense program, even if it takes an hour to gain the same benefits as they would gain from a few all-out intense intervals lasting only a minute or two. However, the amount time it takes to exercise is very important to some people, so they may prefer to suffer in order to gain the benefit of saved time.
Rules for Preventing Injuries During Intense Exercise
Note: These tips for preventing injuries are the same for competitive athletes working at very high intensity and non-athletes doing my modified interval workouts (see below).
• Before every intense workout, warm up by going slowly until your muscles feel fresh. When your training includes intense workouts, your muscles will often feel sore when you start to exercise, but they usually feel better after you warm up for several minutes.
• Do not even start an interval workout when your muscles still feel sore after you warm up for 5-10 minutes or if you feel sick.
• Do not try to do interval workouts on consecutive days or more than two or three times a week. Each time you do interval training, you will probably develop a soreness 6-24 hours after you finish exercising. Physiologists call this Delayed Onset Muscle Soreness (DOMS). If you exercise intensely when you feel DOMS, you are at increased risk for injuring yourself. Skip a planned interval workout if your legs feel heavy or hurt from a previous workout.
• Cooling down means that after you exercise intensely, you slow down and exercise at low intensity for a while before you stop exercising for that session. The scientific literature is controversial on whether cooling down helps to reduce next-day muscle soreness to help muscles to recover faster. I believe that cooling down may help you to heal faster from muscle soreness after intense exercise, which allows you to recover faster from intense workouts. There is some evidence that cooling down augments your immune system response to help muscle fibers heal faster from the Z-line damage caused by hard exercise (Sports Med, July 2018;48(7):1575-1595; Nat Rev Immunol, 2011;11:607-615).
• After each intense workout, get off your feet and do as little walking as possible.
• Try to sleep within a few hours after your intense workout as you may recover faster by sleeping than remaining awake (South African J Research in Sport, Physical Education and Recreation, Jan 2012;34(1):167 – 184). Loss of sleep can impair exercise performance (European Journal of Applied Physiology, April 2017;117(4):699-712).
• Drink fluids for a faster recovery, particularly on hot days (Journal of Sports Sciences, January 2004).
• Add salt on hot days, if your muscles feel excessively fatigued or if you develop cramps (Can J Appl Physiol, 2001;26 Suppl:S236-45).
• Eat as soon as you finish your intense workout (J Sports Sci Med, 2004 Sep; 3(3): 131-138). It doesn't matter what you eat in your post-intense-workout meal, as long as it contains protein and carbohydrates (Am J Clin Nutr, Jan 2017; Med Sci Sports Exerc, Oct 2008;40(10):1789-94). In one study, fast foods such as French fries, hash browns and hamburgers helped athletes recover just as quickly from hard workouts as sports nutrition products such as Gatorade, PowerBars and Clif Bars (International Journal of Sport Nutrition and Exercise Metabolism, March 26, 2015).
• Do not take non-steroidal anti-inflammatory drugs (NSAIDs) to relieve muscle soreness. NSAIDs can block gains in strength and endurance (PNAS, June 27, 2017;114(26):6675-6684; Med & Sci in Sports & Ex, April 2017;49(4):633-640).
Easier Intervals for Non-Competitive Exercisers
A typical interval workout for non-competitive exercisers would be a session of jogging, walking or cycling in which you:
• Warm up by moving slowly for 5 to 10 minutes
• Pick up the pace until you feel a slight burning in your muscles (this usually takes 10-20 seconds)
• Slow down as soon as you feel this muscle burning, and go slowly until the burning is gone and breathing is back to normal
• Alternate picking up the pace for 10-20 seconds and slowing down until you have recovered, and then stopping the workout when your legs start to feel heavy or stiff
If you have not been exercising regularly, spend several weeks exercising at a casual pace. Try to exercise every day and exercise until your legs start to feel heavy or hurt and then stop for the day. You may be able to exercise for five minutes on one day, and then have to take the next day off because your muscles feel sore. You may have a progression of five minutes on one day, then zero on the next day, then 10 minutes, then three minutes and so forth. Gradually you should be able to work up to exercising for 30 minutes every day and not feel sore. Then you should be able to start your interval workouts.
Caution:People with blocked arteries leading to the heart can get a heart attack from intense exercise. Check with your doctor before starting a new exercise program or making a sudden change in the intensity or duration of your program.