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Let us assume that we have two people. The first person starts exercising at 20 years old and continues to do so for the rest of his life. The second person doesn't exercise in his 20's, but when he is 30, begins exercising and continues to do so for his life. Assuming both people survive to 60 years old, will the first person have any advantages over the second, for example improved life expectancy or better metabolism etc?

If possible can you please provide references to back up your claims.

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I don't think that this question is a good fit for our Q&A Format. You should only ask practical, answerable questions based on actual problems that you face. Chatty, open-ended questions diminish the usefulness of our site. Please check the FAQ. –  Baarn Nov 15 '12 at 7:07
Agree, the question needs a bit more work to be answerable. One way of would be to relate more to your specific situation, perhaps something in line with "I am xy years old, haven't exercised, how should I plan to get better at <..>/lose weight ../... and sustain this over more than a decade without <...> side effects of injuries, overtraining.. –  FredrikD Nov 15 '12 at 8:05
@vPeric, I think there are some research, e.g. see the search on Google Scholar for "life long physical training" in this question fitness.stackexchange.com/q/7258/3778 –  FredrikD Nov 15 '12 at 10:46
Here is one reference that shows that training over longer time is good for you, see europepmc.org/abstract/MED/318008/… However, that is hardly a surprise.. –  FredrikD Nov 15 '12 at 10:53
If anyone wants to generalize or otherwise edit the question that's fine, but this is a fine question, perfectly answerable, with specific research and terminology for this in the literature. –  Dave Liepmann Nov 15 '12 at 13:27
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2 Answers

up vote 15 down vote accepted

There are two concerns I see with the person who waits an extra ten years before becoming active.

Sensitive Ages for Athletic Attributes

In his book Science of Sports Training, Tom Kurz goes into several pages of detail on how to maximize the potential of an athlete by matching their age-related susceptibility to certain kinds of development with the appropriate training. As he describes on pages 303 to 304:

At different ages children and youth are most receptive to different stimuli developing different movement abilities. These are so-called "sensitive ages" for a given physical ability (endurance, speed, strength, flexibility, components of coordination). The consequence of not developing a given ability during its sensitive age is reduced fitness and athletic potential lost forever (Drabik 1996).

Specifically, this will determine each individual's ability to realize their maximum lifetime potential in specific types of athletics. From page 305:

In gymnastics, figure skating, and swimming, [the age of maximum realization of the athlete's potential] is between 14 and 20 years. In weightlifting, track-and-field throws, and long-distance running it is between 21 and 30 years. In other sports this age is between 18 and 26 years. These ages are relatively stable, determined by regularities of human growth and maturing, and are not influenced much by the time of starting sports nor by the system of training.

So regardless of other factors, the person who starts working out in their 20s will have the chance to reach their maximum potential, whereas the person who waits will have missed the boat on some specific avenues of maximum athletic potential.

Long-Term Effects of Being Sedentary

There are thousands of studies going into the long-term effects of being inactive. Rippetoe and Kilgore put it best on page 2 of Starting Strength:

Humans are not physically normal in the absence of hard physical effort.

Without running games, carrying and climbing things, random play, contests and sport, people wither. They atrophy in a number of ways too great to detail here. They roll the dice with cancer and heart disease. Their body becomes used to inactivity in its metabolism and its mind, making changes later in life to diet and exercise habits harder.

I could cite studies that talk about the occlusion of arteries and the long-term effects of sitting, but I think we're all clear that there are real health consequences to being inactive for ten years. Perhaps one can mitigate those negative effects by turning their habits around, but it's like smoking: you do immediate good by quitting, but reversing the damage takes a long time. Sometimes it takes longer than you have left.

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Thanks for your answer, and references Dave. I found your section on "Sensitive Ages" particularly interesting. –  Mew Nov 18 '12 at 13:30
@Chris Thanks. I was pretty floored when I read it the first time. Makes sense, but it's not obvious, and has broad-spanning implications. –  Dave Liepmann Nov 21 '12 at 20:02
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It is beneficial to delay the weight increase you would otherwise get with aging, since the set point weight would increase.

For instance, if you are 75kg at age 20 and that is a "good" weight, if you increase to obese 85kg at age 30, you are in a worse position than if you had exercised more and only increased to 80kg.

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