Get Moving!

Learning Objective (LO):  What are the effects of prolonged inactivity and what are the implications of this on everyday living?

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Main take home messages:

  • being sedentary for long periods of time can increase your risk of developing Type 2 Diabetes (T2D) via decreased skeletal muscle insulin sensitivity, increased visceral fat mass, decreased muscle mass
  • sitting for too long is not the same as not getting enough exercise
  • exercise and regulating food intake may help to negate some of the effects of prolonged sitting but they are not enough, therefore…
  • move more! “moving” can be as simple as:
    • walking up the escalator instead of just standing on it while it brings you up
    • parking a little further from the store so you get to walk a bit more
    • getting up to stretch or walking around during commercial breaks if you’re watching TV

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This was one of our first LOs that we did and I came across some research I found particularly interesting that I was not aware of before. This research implied that perhaps we should have guidelines for not just the minimum amount of regular physical exercise per week but also the maximum time spent sitting per week. There were some other effects of prolonged inactivity (more MSK-related), shown in Table 1, as well but I won’t be discussing them here.

Effects of prolonged inactivity Source(s)
Bone loss (1)
Loss of muscle mass (greater loss with immobilization than bed rest or limb suspension; antigravity muscles most susceptible) (2)
Loss of strength (not just due to loss of muscle mass but also due to neural adaptations) (2)
Decrease in tendon stiffness (2-4)
Potential differences in response to prolonged inactivity in men vs women (2)
Table 1: Some effects of prolonged physical inactivity

There are several models that can be used when studying the effects of prolonged inactivity in humans (5):

  • stopping daily endurance exercise in endurance athletes
  • inducing bed rest
  • increasing sitting time
  • lowering daily ambulatory activity (i.e. # steps taken/day)

Of these models, increasing sitting time and lowering daily ambulatory activity seem most representative of how humans become more inactive in their daily lives and thus are probably more realistic when determining how physical inactivity can affect our health. While inducing bed rest and stopping daily endurance exercises in endurance athletes can have interesting results, the findings would likely overestimate the effects of prolonged physical inactivity. That being said, they can be useful for studying the mechanisms behind the effects (6) so I will be including results from bed rest studies in my discussion.

Thyfault et al. (6) conducted a literature review of the existing evidence that physical inactivity is harmful to health. I’ve summarized the main results found for each model used below as well as the implications of the results:

Model Results of Studies Implications on Everyday Living
Short-term bed rest (9 days)
  • reduced skeletal muscle insulin sensitivity
  • altered expression of more than 4500 genes in mRNA of skeletal muscle after bed rest(1)
  • some of the genes down-regulated included those that are normally found to be suppressed in T2D patients
  • after a 4 week exercise program, the expression of 17% of these genes altered by bed rest had not fully returned to their pre-bed rest levels
  • stimulation with insulin after bed rest resulted in greater up-regulation of gene expression for inflammatory pathways connected to the development of T2D, despite reduced insulin sensitivity
Prolonged inactivity may increase your risk of developing T2D by reducing skeletal muscle insulin sensitivity and up-regulating inflammatory pathways involved with the development of T2D. These changes may take much longer to fully undo than it does for them to occur, implying that this increased susceptibility could take very long to return to normal…so be preventative, not reactive, and get moving!Note: skeletal muscle insulin sensitivity is important because skeletal muscle is a major glucose uptake site after eating a meal (7)
Increased sitting time
  • significant direct association between sedentary time and metabolic risk, regardless of the amount of time spent doing moderate-to-vigorous intensity activity
Consider not just increasing the amount of time you spend exercising, but also the minimizing the amount of time you spend sitting.
Increased sitting time
  • sedentary condition 1: participants who had one highly sedentary day and a positive energy balance (i.e. energy intake > energy expenditure)
  • sedentary condition 2: participants who had one highly sedentary day and a reduction in energy intake so that energy intake = energy expenditure
  • highly physically active condition
  • level of insulin resistance measured for each of these conditions: sedentary condition 1 > sedentary condition 2 > highly physically active condition
If you expect to be sitting all day, eating less will partially, but not fully, help to offset the increase in insulin resistance that will occur (due to sitting all day)
Reducing ambulatory activity (<1500 steps/day for 2 wks)
  • significant decrease in skeletal muscle insulin sensitivity (but not hepatic insulin sensitivity)
  • increase in visceral fat mass
  • decrease in VO2max
  • decrease in leg lean mass
Visceral fat mass has been linked to increased risk of T2D and cardiovascular disease. Loss of peripheral insulin sensitivity, VO2max, and leg lean mass is also important to note as they have been linked to increased morbidity and mortality. Walking more may help to decrease your risk of developing T2D.

After reading that review and learning about these negative effects of prolonged physical inactivity, I had a couple more questions:

1. What effect does exercise have to help to offset these negative effects?

  • I suspect that, similar to reducing energy intake, increasing amount of time exercising (or performing “moderate-to-high intensity physical activity”) will help to partially, but not fully, offset the effects
  • Traditional continuous aerobic training, high intensity interval training, and resistance training have all shown to improve insulin sensitivity (8)

2. Does taking breaks over long sedentary periods (e.g. get up once an hour) help to offset these effects?

  • according to Dunstan et al. (9), there are no definitive recommendations on how long people should sit or how frequent their breaks should be
  • however, studies have shown a significant difference in waist circumference when comparing those who took a lot of breaks (top 25% in the ‘break’ distribution) and those who took very few (lowest 25%)

So what does all this research mean?

Personally, I used to think that since I went to the gym a lot, it would be okay to take the elevator instead of the stairs, or to take the bus instead of walk to school. However, I now realize that being healthy is not just about the amount of time you spend exercising, but also the amount of time you spend sitting, as this can greatly influence your risk of developing T2D. Since learning about this, I now take the extra effort to avoid sitting for extended periods of time and to walk whenever possible. Thank goodness I don’t have many long lectures to sit through anymore!

To reiterate the take home messages:

  • being sedentary for long periods of time can increase your risk of developing Type 2 Diabetes (T2D) via decreased skeletal muscle insulin sensitivity, increased visceral fat mass, decreased muscle mass
  • sitting for too long is not the same as not getting enough exercise
  • exercise and regulating food intake may help to negate some of the effects of prolonged sitting but they are not enough, therefore…
  • move more! “moving” can be as simple as:
    • walking up the escalator instead of just standing on it while it brings you up
    • parking a little further from the store so you get to walk a bit more
    • getting up to stretch or walking around during commercial breaks if you’re watching TV

Note: I am not saying that exercise and being aware of what you eat are not important. I am merely highlighting another important factor that contributes to health and is less well-known.

I hope everyone has a happy Thanksgiving and can take some time to get moving! It might even help your waistline ;).

Questions/comments/concerns? Feel free to leave a comment below or send me an email! Feedback is always appreciated :).

References

1.     LeBlanc AD, Spector ER, Evans HJ, Sibonga JD. Skeletal responses to space flight and the bed rest analog: a review. J Musculoskelet Neuronal Interact. 2007 Jan;7(1):33–47.

2.     Clark BC. In vivo alterations in skeletal muscle form and function after disuse atrophy. Med Sci Sports Exerc. 2009 Oct;41(10):1869–75.

3.     Matsumoto F, Trudel G, Uhthoff HK, Backman DS. Mechanical effects of immobilization on the Achilles’ tendon. Arch Phys Med Rehabil. 2003 May;84(5):662–7.

4.     Trudel G, Koike Y, Ramachandran N, Doherty G, Dinh L, Lecompte M, et al. Mechanical alterations of rabbit Achilles’ tendon after immobilization correlate with bone mineral density but not with magnetic resonance or ultrasound imaging. Arch Phys Med Rehabil. 2007 Dec;88(12):1720–6.

5.     Thyfault JP, Krogh-Madsen R. Metabolic disruptions induced by reduced ambulatory activity in free-living humans. J. Appl. Physiol. 2011 Oct;111(4):1218–24.

6.     Thyfault JP, Booth FW. Lack of regular physical exercise or too much inactivity. Curr Opin Clin Nutr Metab Care. 2011 Jul;14(4):374–8.

7.     DeFronzo RA, Tripathy D. Skeletal muscle insulin resistance is the primary defect in type 2 diabetes. Diabetes Care. 2009 Nov;32 Suppl 2:S157–63.

8.     Roberts CK, Little JP, Thyfault JP. Modification of insulin sensitivity and glycemic control by activity and exercise. Med Sci Sports Exerc. 2013 Oct;45(10):1868–77.

9.     Dunstan DW, Thorp AA, Healy GN. Prolonged sitting: is it a distinct coronary heart disease risk factor? Curr. Opin. Cardiol. 2011 Sep;26(5):412–9.

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10 comments to this article

  1. Going Here

    on October 13, 2013 at 4:10 pm - Reply

    Incredibly informative….looking forwards to visiting again.

    • veewong

      on October 14, 2013 at 12:01 pm - Reply

      Thanks! I’m glad it was useful 🙂

  2. Dan Ogborn

    on October 13, 2013 at 6:14 pm - Reply

    Wow, are all your notes this organized? Nice work. Very important point that there is a distinction between what constitutes physical activity and sedentary behaviours. You may want to check out the systematic review by Thorp et al (2011) that indicates that increasing physical activity time may not offset the effects of increased sedentary behaviours (sitting time, TV-viewing time) on mortality among other effects.

    • veewong

      on October 14, 2013 at 11:52 am - Reply

      Thanks for the reference, I’ll check it out!

    • VeeWong

      on October 21, 2013 at 8:48 pm - Reply

      Hmm so I just read the review and it says that, “there is insufficient evidence to conclude that a longitudinal relationship exists between sedentary behavior, markers of cardiometabolic health, and metabolic syndromes” (including insulin resistance). Quite different from what Thyfault et al (5, 6) say! I’m confused. Oh actually, I guess what Thyfault et al are saying is that an acute increase in sedentary time leads acute physiological changes that are also commonly observed in Type 2 Diabetics; therefore, chronic sedentary behaviour could potentially lead to Type 2 Diabetes. However, according to Thorp et al, this has yet to be shown in the evidence.

  3. Shawn

    on October 15, 2013 at 10:57 pm - Reply

    Very interesting and well presented!

    I am curious to know what kinds of physical activity are most effective at offsetting long periods of sitting.

    • VeeWong

      on October 20, 2013 at 8:49 pm - Reply

      Good question! In Roberts et al. (8), they discuss a theory for why high intensity interval training can be more effective at increasing insulin sensitivity than low/moderate intensity exercise (typical continuous aerobic training):

      “As mentioned previously, it is well known that skeletal muscle plays a major role in whole-body glucose disposal, and insulin resistance in skeletal muscle is recognized as a key contributor to impaired glucose control in T2D (23). As such, there is theoretical rationale for why high-intensity exercise may have greater benefits for im- proving insulin sensitivity and subsequent glucose control. High-intensity exercise requires a greater degree of muscle fiber recruitment and more rapidly depletes muscle glycogen stores in all types of muscle fibers (75). These combined effects would be hypothesized to result in a more robust stimulation of postexercise muscle glucose uptake and glycogen resynthesis when compared with low- or moderate-intensity exercise.”

      That being said, I don’t know of any studies directly comparing different types of physical activity and their effectiveness at offsetting changes in insulin resistance…but it’s definitely something to look out for!

  4. Frances

    on October 17, 2013 at 2:28 pm - Reply

    Moving more keeps you healthy – this is quite true.
    I know for a fact that when I am more physically active during the day – walk more, gardening, line dance, house cleaning – I sleep better and more deeply.

  5. Kathy

    on October 20, 2013 at 8:49 pm - Reply

    Great article!

    I think the largest group at risk are the 9-5 office workers. I converted to a stand-up table at work, and I was surprised that most people found it strange that I was standing, and no one mentioned that they heard how bad sitting is for you.

    It’ll probably take time for companies to pick up on this, but it would be good to see more stand-up desks incorporated into the traditional office setting, or even just a greater emphasis on spreading the message to move every so often. Companies could install the applications that remind people to take moving/standing breaks after a set time.

    • VeeWong

      on October 20, 2013 at 8:59 pm - Reply

      Haha yea! Install an application that doesn’t let you use the computer for 2 minutes so you’re forced to get up and do something else for that time :p. I suppose one problem with that is that it would interrupt people’s concentration, especially if they’re in a state of “flow”, and that might impact productivity…?

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