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By Dr Sarah Shultz.
This World Obesity Day, I think it is important to discuss one of the more commonly recognised aspects of weight management interventions: exercise. Exercising for health is not a new concept, and there are physical activity guidelines available across the globe; typically, an adult should spend 150 minutes each week doing (at the least) moderate intensity activity to maintain and improve health outcomes.
There are also physical activity recommendations if the individual wants to prevent weight gain (150-250 minutes/week) or lose a clinically significant amount of weight (225-420 minutes/week). The amount of physical activity recommended is almost exclusively determined by the cardiovascular and metabolic benefits resulting from exercise, and with good reason. The guidelines promote improvement of obesity-related health risks (heart disease, type 2 diabetes) that can decrease an individual’s lifespan. But what if, in an effort to prescribe exercise that promotes physiological results, health professionals ignore the musculoskeletal system that must function during the activity?
Biomechanics is the study of the interactions between forces and motion, and the implications of those interactions on human (and other biological) life. As a biomechanist, I want to know how additional weight changes the way obese people are able to move and function in life. I realise this topic is fairly narrow, especially compared against the many different factors that are associated with both gaining and losing weight, but I believe that understanding a person’s ability to be physically active will actually play a major part in how physically active they are.
In my opinion, the amount of energy spent during exercise is irrelevant if the person refuses to attempt the exercise because he/she cannot physically complete the task or has joint or muscle pain when exercising. Given that muscle/joint/bone pain has been reported in obese people of all ages, and even as young as two and three years old, the implications for pain and dysfunction as an obstacle to exercise are extremely relevant — and are not given the consideration they are due.
The belief that weight loss will improve musculoskeletal pain and functioning can be easily supported by biomechanics, and Newton’s third law of motion: for every force, there will be an equal and opposite reaction force. If weight is lost then there is less mass and less gravitational force pushing down, which means less reaction forces that the individual must absorb, particularly at the joints. This theory has been scientifically quantified in weight loss: when approximately 0.5kg of body weight is lost, four times less load will be applied to the knee joint.
Benefits can even be seen when weight is lost without exercise: physical function, musculoskeletal pain, and joint range of motion have all improved within six months of bariatric surgery. But surgery is expensive and extreme. Modifiable lifestyle factors like diet and exercise are much more common treatments for weight management. Short and infrequent bouts of exercise can make the pain worse, but routinely participating in exercise can improve pain, perceived and actual physical function, and quality of life.
So if exercise is confirmed to improve musculoskeletal health, along with benefiting the cardiovascular and metabolic systems, then it is not a question of if exercise is prescribed, but rather how exercise is prescribed. The beauty of the guidelines is in their flexibility; like so many aspects of obesity, exercise prescription must be specific to the individual. Aerobic exercise (running, biking, swimming, or any exercise that is continuous and rhythmic) improves the possibility of weight loss and body fat reduction, but the amount of weight-bearing force associated with more traditional activities (running, walking) can impact pain. Resistance training can be completed with minimal pain, and improve strength and stability. Both types of exercise can be modified to accommodate acute pain, as can the duration, frequency, and intensity of the exercise.
The important part is not what exercise is being completed or the amount of energy being expended, but that exercise is not a chore someone has to be bullied into completing. If the “right” exercise is used – one that can be completed, enjoyed and will cause no pain – and the time spent exercising is extended in a reasonable way (no more than a 5-10 per cent increase each week) then it will become part of daily life. And isn’t the point of modifiable lifestyle factors to change and sustain a person’s attitude towards healthy living?
Dr Sarah Shultz is a senior lecturer from Massey University’s School of Sport, Exercise and Nutrition.
Created: 10/10/2017 | Last updated: 10/10/2017
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