Why do the NHS guidelines recommend doing muscle-strengthening activity twice a week?
Well, as with the other recommendations, there is quite a bit of evidence that seems to show that muscle strengthening activity has a number of health benefits, which we will try and demonstrate in this video.
Firstly, research has shown that certain types of muscle-strengthening activity have numerous effects on the bones and the muscles which improve health. In this video, we will go over this in more detail, focusing on the bones and will focus more on the muscles in the next video, even though they are both related when it comes to muscle-strengthening activity, it is easier to just focus on one at a time.
What is muscle-strengthening activity?
Well as the NHS guidelines say, it is any activity that makes your muscles work harder than usual.
There are many other names for it though and many types of sports or methods of exercise would fall into the strength training category including: resistance training, weight training/bodybuilding, some forms of Pilates/yoga among others.
This is easier to understand when you consider that muscle –strengthening activity is usually any activity where you are working against a moderate-heavy load to move it (this can also include your own body).
What effects does muscle –strengthening activity have on the skeletal system (bones)?
It’s important to realise that during muscle-strengthening activity, the bones and the muscles work together to move objects (be it a weight, your own body etc. from A to B).
For example take the biceps muscle, which attaches on the scapulae and inserts on the lower arm bone (the radius) as you can see in the diagram in our video. As it contracts, this causes movement of the bones. (So the muscles create the power, and the bones provide the structural support for the muscles to apply this power).
So imagine this muscle is moving a moderately heavy weight, this stress is transferred through the muscle into the tendons which attach the muscle to the bone, and therefore that stress is also applied into the bone. Obviously, if this kind of activity is repeated on a regular basis, this will have some effects on the bone itself (and of course the muscle, but we will cover that later!)
To understand these effects, it’s important to understand what bone is actually made of. Bones are a living tissue so are constantly building and re-building as time passes
The bone is made up of sponge-like inners/marrow (trabecular bone) and a harder, semi-flexible outer shell (cortical). (Again, have a look at the diagrams in our video)
The cells responsible for increasing the density of bones are called osteoblasts and these react to increased stress on the skeleton and hormonal changes by producing more bone cells (Kawao and Kaji, 2015).
This means that as you exercise more and increase your muscular strength, the bones become stronger and less likely to break.
Who benefits most from muscle strengthening exercise?
Everybody can benefit from taking part in muscle strengthening activity which is why it is recommended for adults.
People under the age of 16 CAN take part in muscle strengthening activity but should avoid certain forms of resistance training (such as high impact activities,-unless they are supervised by a qualified coach).
However, there is one group of people that muscle strengthening activity is extremely important for- and that is women.
We will explain why this is in more detail now, but basically it has to do with the hormonal changes that happen during the menopause, when the amount of oestrogen produced by the body drastically drops.
In both men and women, up until the age of 30 people naturally produce more bone than they lose, then by about the age of 35, this gradually reverses until bone loss then becomes more advanced than bone production (Svejme et al., 2014, Mori et al., 2014) (i.e. bone mineral density BMD decreases).
So as we age, the holes in the spongey portions of our bones gradually become larger, thus making the bones more hollow and weak, and once they reach a certain point, they are classed as having the disease called osteoporosis- which is basically bone that is so weak and low in BMD that it is at high risk of fracture even with a light i.
But women are 4 times more likely to develop osteoporosis than men are. One reason for this is they naturally have lighter more delicate skeletons than men in the first place (lower BMD) But a big factor in this is the role oestrogen plays in bone production-and the sudden reduction of this hormone during and following the menopause (Finkelstein et al., 2008).
So since our bones are constantly working to keep our structure, they are also constantly needing to be re-built and patched over throughout our lives, even though we might never have a noticeable fracture or injury, tiny cells in our skeleton are constantly working to maintain our bones. These cells are known as osteoblasts and osteoclasts, and work together by the osteoclasts first breaking down old bone, before the osteoblasts build new bone to replace it.
Basically, this lack of oestrogen has a knock-on effect on the signalling hormones which regulate bone growth.
The normal interaction between the osteoblasts which build bone, and the osteoclasts which break down bone, making the osteoclasts more active than the osteoblasts meaning bone breakdown happens much faster than bone formation-and this is on top of the already reduced rate of bone production naturally experienced due to ageing.
A growing amount of scientific evidence is showing us that if women take part in regular resistance training such as weight lifting, they can significantly reduce their risk of developing osteoporosis in later life when compared to women who don’t do this. The term “weight-bearing activity” is often use to describe the types of physical activity that are good for protecting against osteoporosis development. This basically describes any exercise where the body must bear weight as the name suggests (whether this be your own bodyweight, or additional weight such as gym equipment). Examples of this include running (your legs and hips are bearing the additional weight created by the force of your feet contacting the ground at speed), lifting weights, dancing, football/tennis. Although these activities are not necessarily resistance training, because your bones are required to deal with fairly high impact forces due to jumping, running and changing direction, good changes to your BMD are likely to take place to accommodate these types of activity (Zhao et al., 2014).
So are there any exercises that don’t help improve BMD?
Unfortunately, some perfectly good forms of physical activity are not as effective at protecting against osteoporosis as others, simply due to the fact that they do not require the same amount of weight-bearing activity required to allow the bones to adapt and increase BMD. For example, there is some scientific evidence that shows cycling is not as effective at preserving BMD as other activities such as the ones previously mentioned (Nagle and Brooks, 2011). This is because when you are cycling, you are not putting enough stress on your skeleton since- 1, you are usually sitting down and 2, the action of pedalling a bike is smooth and doesn’t include impacts which stress the bones enough to cause increases in BMD. This is not to say that cycling is bad for you-cycling is an excellent form of exercise and has many benefits to the cardiovascular and muscular system, as well as some positive effects on bone health. But if you cycle, make sure you are doing other activities to strengthen your bones too.
We hope you have learned something from this blog, look out for our next episode of the Evidence Exercise next week!
Resources:
FINKELSTEIN, J. S., BROCKWELL, S. E., MEHTA, V., GREENDALE, G. A., SOWERS, M. R., ETTINGER, B., LO, J. C., JOHNSTON, J. M., CAULEY, J. A. & DANIELSON, M. E. 2008. Bone mineral density changes during the menopause transition in a multiethnic cohort of women. The Journal of Clinical Endocrinology & Metabolism, 93, 861-868.
KAWAO, N. & KAJI, H. 2015. Interactions between muscle tissues and bone metabolism. Journal of cellular biochemistry, 116, 687-695.
MORI, T., ISHII, S., GREENDALE, G. A., CAULEY, J. A., STERNFELD, B., CRANDALL, C. J., HAN, W. & KARLAMANGLA, A. S. 2014. Physical activity as determinant of femoral neck strength relative to load in adult women: findings from the hip strength across the menopause transition study. Osteoporosis international, 25, 265-272.
NAGLE, K. B. & BROOKS, M. A. 2011. A systematic review of bone health in cyclists. Sports Health: A Multidisciplinary Approach, 1941738111398857.
SVEJME, O., AHLBORG, H. & KARLSSON, M. 2014. Physical activity reduces bone loss in the distal forearm in post‐menopausal women–a 25‐year prospective study. Scandinavian journal of medicine & science in sports, 24, 159-165.
ZHAO, R., ZHAO, M. & ZHANG, L. 2014. Efficiency of jumping exercise in improving bone mineral density among premenopausal women: a meta-analysis. Sports medicine, 44, 1393-1402.
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“The Evidence Exercise” is a nine-part series focusing on the research and evidence for including physical activity in our lives.
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