Exercise for Both Endurance AND Intensity

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    For maximum health benefits, you should work for both endurance and intensity in your exercise program. We have lots of evidence that exercise prolongs lives by reducing risks for chronic diseases such as high blood pressure, heart attacks and diabetes (PLoS Medicine, January 12, 2021), and adding intensity to a workout increases its health benefits (Brit Med J, Oct 7, 2020;371).

    A recent study from the University of Guelph in Ontario, Canada suggests that you will gain more health benefits by trying to exercise intensely on some days and doing slower recovery exercise on the other days (Med Sci Sports Exerc, June 2021;53(6):1194-1205). In this study, 23 overweight participants were divided into two groups that exercised on stationary bicycles for six weeks:
    Endurance Group: Five days a week, 30–40 minutes of continuous exercise at about 60 percent of maximal effort
    Intense Intervals Group: Three days a week, 4-6 intervals with each lasting for 30 seconds at almost all-out intensity, with a two-minute recovery between each interval.

    The researchers found that both the endurance group and the intense intervals group had increased heart-lung fitness and ability to control blood sugar levels after eating a meal, but only the endurance group had lower blood pressure, decreased body fat, and ability to control blood fat levels after eating a high-fat meal. This shows us that short bouts of intense exercise alone are not enough; your exercise program should include both some endurance work (time and distance in your activity) and some short bursts of intensity (increased effort).

    Stress and Recover
    I recommend that exercisers at all levels should follow a stress and recovery exercise program. Competitive athletes need to exercise every day to gain maximum strength, and they know that they have to exercise intensely to improve in their sport. They quickly learn that exercising intensely damages muscles to cause delayed onset muscle soreness (DOMS) and they need to follow each intense workout with less intense recovery workouts.

    You will become more fit by taking a hard workout and then going at low intensity for a day or two than you will by exercising at the same leisurely pace every day. You have to damage muscles to gain strength and enlarge muscles. Every muscle is made up of thousands of fibers like a rope is made of many strands. Every fiber is made up of blocks called sarcomeres that fit end to end like a row of bricks. Sarcomeres butt upon each other, end-to-end, at Z-lines (Diagram). Muscles contract only at each Z-line. When you exercise vigorously, you damage these Z-lines and when they heal, the muscle fibers are stronger, so all knowledgeable athletes take some intense workouts to damage their muscles at the Z-lines. On the next day their muscles are sore and damaged and they exercise at a relaxed pace. When the muscles are healed and the soreness lessens, they take their next intense workout. If athletes exercise at low intensity during the healing phase of the Z-lines, their muscle fibers will become stronger than if they rest. If they exercise vigorously when their muscles are sore, they are likely to tear them and become injured.

    Non-Athletes Also Should Exercise Every Day
    Forty percent of North Americans die of heart attacks. One of the most common causes of the arterial damage that precedes heart attacks is a high rise in blood sugar after meals. Resting muscles remove no sugar from the bloodstream, but contracting muscles remove sugar rapidly from the bloodstream without even needing insulin. This effect is strongest during exercise and diminishes to no benefit about 17 hours after you finish exercising. If you want to use exercise to help control blood sugar, you need to do it every day.

    An Exercise Program for Everyone
    CAUTION: Because a person with blocked arteries leading to the heart could suffer a heart attack during exercise, please check with your doctor before starting a new exercise program or increasing the intensity of your existing program. Whatever activity you choose, try to exercise every day. If you are just starting out, spend about six weeks at a slow pace until you are comfortable in your activity for thirty minutes or more. Then you are ready to alternate more intense days with easier workouts.

    Intense Days: Stress refers to intensity, not the length of your workout. You can gauge the severity of the stress by how hard you breathe and by the amount of burning you feel in your muscles during exercise. Interval training means that you start out slowly, pick up the pace, slow down immediately when your muscles start to burn, recover by going very slowly for as long as you want, and then pick up the pace again.
    • On your hard days, warm up by going very slowly for five to 10 minutes. Going slowly at the start of a workout warms up muscles to help make them resistant to injury. If your muscles still feel tired or heavy, do not try interval training. Exercising with tired or sore muscles can cause serious injuries.
    • After you warm up, pick up the pace gradually until you feel burning in your muscles and immediately slow down. Then go at a very slow pace until the soreness goes away, your breathing returns to normal and you feel recovered. How long it takes to recover is irrelevant. You take your next faster pick up when you feel that you have recovered, not from any preset time. Then pick up the pace until you feel burning again.
    • If you are not planning to compete, you do not ever need to go at 100 percent intensity. People who are just starting to do interval workouts should pick up the pace only slightly and not become short of breath. Slow down and get out of the burn as soon as you feel it. As soon as the burning and fatigue go away, and you are not breathing hard, try to pick up the pace again. In early workouts, you may only be able to do one hard pickup. Do not start your next pick up until your legs feel fresh. As soon as your legs start to feel heavy, stop the workout. Trying to increase the pace when your muscles feel sore, or trying to work through heavy or tired muslces invites injury.

    Easy Days: The day after your hard workout, your muscles will probably feel sore and you should take an easy workout. If the discomfort does not go away after you warm up, is worse on one side of your body, or increases as you exercise, stop exercising immediately and cool down. You could be injured and continuing to exercise will delay healing. If you feel better as you exercise casually, continue to exercise until you feel any discomfort or heaviness. Always stop every workout when your muscles hurt or feel heavy. Keep on taking easy days where you exercise at low intensity until you feel fresh again.

    My Recommendations
    I believe that every healthy person should try to exercise every day. You will gain a much higher level of fitness by “stressing and recovering.” Exercise more intensely on one day and go slowly on the next day or days. Only when your muscles feel fresh should you try to pick up the pace again.