The answer to the question depends on the type of exercise.
A few years back Laurence participated in the New York City Triathlon. He did well but didn’t win his age group. Three years later, he finished 24th overall in the New York City Triathlon overall and finished first in his age group, 45 to 49. He beat his nearest competitor by over five minutes.
He attributed a large part of his success to HIIT, high intensity interval training, a strength/cardio workout taken to a deep fatigue. He had been doing it four years along with his usual swimming, running, biking, and kayaking. His times in triathlon events came down. The strength training program enabled him to spend less time on his bike and in the pool. More time for recovery resulted in continuing improvement.
I am stronger, recover faster and only devote 30 minutes a week to weightlifting. It is like discovering the fountain of youth. It really does work.
Ted was a gifted runner. In his late forties his knees began to aggravate him, and they got worse each year. At age 54 his doctor advised him to stop running. He started strength training with the aim of getting back to running.
We worked around his condition for a while and slowly incorporated leg exercises into the routine - leg curl, calf raises, leg press, adduction, abduction, squats, and occasionally partial leg extensions.
Ted wanted to start running again. He did and the next day his was limping again. I told him, “You are able to lift 450 pounds on the leg press to a very deep fatigue to the point where your legs are unable to move, and the next day you have not a hint of pain.” For Ted with adequate rest after strength training he came back stronger each week. With running there was no recovery or improvement, only injury.
I once asked a trainer what he was trying to accomplish with his clients. He said, “I'm there to get them stronger and to improve their health.” I told him I didn't need him for that. I can buy running shoes and head out the door. I can go to gym and pick up weights. He countered that he was there to teach clients how to exercise correctly. I came back with the fact that anyone can go to the bookstore and buy any number of books on how to do it correctly.
I don't know what the role of a trainer is in other systems or gyms. There are several ways of approaching it. My thoughts on the subject have been shaped by my interactions with clients. A client once told me I come here to get a workout I could not get on my own. She said, “If I can do it on my own I don't need you anymore”. That really stuck with me.
I had another client whom I told, “You know you could figure this out on your own”. She replied, “I have two businesses and three kids. I pay you to figure it out for me”.
I think both are correct.
From this article in the International Journal of Obesity, High-intensity intermittent exercise attenuates ad-libitum energy intake comes this conclusion:
“High-intensity intermittent exercise suppresses subsequent ad-libitum energy intake in overweight inactive men. This format of exercise was found to be well tolerated in an overweight population.”
The study compared a group of over-weight men who did moderate exercise to another over-weight group who did high intensity interval exercise (HIIT). Seventy minutes after they exercised the HIT group consumed fewer calories and also consumed fewer calories the next day.
From this article, Short workouts: Will exercising for 15 minutes once a week get you fit? are some quotes and responses after the quotes.
“It sounds too good to be true”
If something is too be good to be true then it follows that it really is too good to be true. The truth is the workouts are very demanding, but they won’t take a lot of your week. Anyone with proper instruction can do it though: you build up to it slowly. Our oldest client was 95 years old.
“Over the past decade, many trainers have begun advocating for shorter, less-frequent workout regimens – claiming that they are much more efficient for weight loss and muscle building.”
High intensity of aerobic exercise lowers blood pressure more that low intensity aerobic exercise. That has definitely been my experience. From this study,
“This study indicates that the blood pressure reducing effect of exercise in essential hypertension is intensity dependent. Aerobic interval training is an effective method to lower blood pressure and improve other cardiovascular risk factors.”
From this article Short workouts: Will exercising for 15 minutes once a week get you fit?
“The key to the short workout’s success revolves around a concept known as high-intensity interval training (HIIT). HIIT is a heightened form of interval training that involves alternating between periods of short, intense physical activity and fixed periods of low activity or rest. Intervals can include anything from fast squats and pushups to weight lifting and powerful cardio.”
The goal in exercise is expose the body to more than it is used to handling. If given enough time for recovery the body as a form of self-protection will come back stronger, more enduring, and more able to withstand the stresses previously placed on it. That can take one hour or two, or it can take less than ½ an hour. Regardless of the time period at the end the session you want to come out spent.
Exercises are performed in all sorts of ways. Expose your body to more work that it is used to handling, allow rest and recovery and the body will make a positive adaptation as a form of self protection. You can put in more time – do more reps, do more sets, run a little further, engage in whatever the activity is a little longer – and as long as you don’t overdo it the body will come back improved.
You can work a little harder – more weight on the bar, a steeper hill at the same pace, sprinting instead of jogging - and again as long as you don’t overdo it the body will come back improved. If you exercise in this way the workouts cannot be very long but they can be very effective. Just one benefit is fat loss.
From this study, High-Intensity Intermittent Exercise and Fat Loss this quote:
From this article this quote: Exercise: The News You Don't Want to Hear
“A much better and more efficient way to exercise -- and one that research is clearly showing works a lot better -- is to do high-intensity circuit training. Put the beauty bells down and lift some iron. Shorten your rest periods. If you're doing "aerobics," do some interval training where you sprint for a while then jog to catch your breath.
And by the way, forget about "toning." It doesn't exist. You're either building muscle, maintaining the muscle you already have, or your muscles are slowly shrinking. The first two are accomplished with weight that's heavy to lift. The third is accomplished by doing nothing.