To discourage us from eating the wrong foods we are often told what exercise would be required to burn the food item off. We have been told that if we eat that chocolate bar we will have to go to the gym and work for at least an hour at high intensity to pay the price. Conversely we are also told that working out at the gym or in the park at high intensity is the best method for weight reduction.
It makes sense that the harder you work the more kilojoules you will burn, and it has to be correct because we see it on television!!
The question is how do we measure these claims?
The American College of Sports Medicine (ACSM) is one of the most revered professional colleges on the planet. They have led the exercise science revolution for the past 60 years. In recent years they have promoted a series of calculations to measure your energy expenditure and to answer these questions.
I would like to present a case study to you with calculations and numbers that might help us answer these questions and frighten us with the answers.
Just because I mentioned calculations and numbers PLEASE don’t leave me now as we are just getting to best part….. work with me!!
Say Hi to Peter
I would like to introduce you to my friend Peter.
Peter is a 45 years old high-powered executive who has body fat percentage of 37%. He weighs 110 kilograms and is 173 cm tall and has a BMI is 34 kg.m-2 which classifies him as obese. Peter has increased his body weight over the past three years mainly due to his sedentary lifestyle. Peter does no exercise at all and eats at restaurants for lunch on most days. Peter has been diagnosed with early osteoarthritis in both knees and has been experiencing acute low back pain.
Peter has been told by his physician to lose weight.
Upon examination of the lifestyle and health risk questionnaire that Peter completed during his profile appraisal, it was noted that he was classified as moderately at risk. This was decided upon by the two risk factors of obesity and sedentary lifestyle that he demonstrated.
Peter’s fitness appraisal reported a resting heart rate of 80 beats per minute and maximum heart rate of 175 beats per minute. A submaximum VO2 max cycle test indicated his aerobic capacity to be 30 ml.kg.min-1.
The initial realistic goal that Peter should strive for is a reduction in body fat to 30%.
To determine Peter’s goal weight we can use the following equation:
Goal weight = (current weight) x (1- current % fat)
(1- desired % fat)
Goal weight = (110 kg) x (1-.37)
Goal weight = 110 kg x (.63)
Peter’s Goal weight = 99 kg
When developing Peter’s exercise prescription it is important to note his osteoarithitic knees by encouraging him in non-weight bearing exercise. Peter has a background in cycling and has decided that his focal exercise mode will be cycling in the cardio theatre environment.
This exercise session performed 5 days per week is the main weight loss intervention that Peter will be prescribed.
Peter’s initial level of aerobic fitness is quite low (30 ml.kg.min-1) and as such he should exercise at an intensity within a heart rate range of between 60% – 70% HRR.
Peter’s target heart rate during his exercise session will be:
Target heart rate (lower level) = (intensity fraction) x (HR max- HR rest) + HR rest
Target Heart rate (lower level) = (.60) x (175-80) + 80
Target heart rate (lower level = .60 x 95 + 80
Peter’s target heart rate (lower level) = 137 beats
Target heart rate (upper level) = (.70) x (175-80) + 80
Target heart rate (upper level) = .70 x 95 + 80
Peter’s target heart rate (upper level) = 147
Peter’s target heart rate range = 137 – 147 beats per minute
For Peter to maintain his heart rate between 137 – 147 beats per minute, he must pedal on the bike at 90 watts or 540 kg.m.min-1 (one watt is approximately equal to 6 kg.m.min-1).
What is Peter’s oxygen consumption?
We can determine this by using the following calculation:
VO2 = 7 + 1.8 x (work rate in kg.m.min-1)
VO2 = 7 + 1.8 x (540 kg.m.min-1)
VO2 = 7+ 972
VO2 = 979
VO2 = 8.9 ml.kg.min-1
This indicates that when Peter cycles on the stationary cycle at a heart rate between 137-147 beats per minute at 90 watts he will consume 8.9 ml.kg.min-1.
Convert 8.9 ml.kg.min-1 to litres of oxygen per minute
= (8.9 ml.kg.min-1) x (110 kg) = .98 litres of oxygen per minute
To calculate the number of kilocalories expended per minute multiply litres per minute by 5 Kilocalories expended (20.9 kJ) = .98 x 5 = 4.9 kilocalories per minute (20.5 kJ)
If Peter exercises on his stationary cycle for 60 minutes per session he will expend (4.9 kilocalories per minute x 60 minutes) = 294 kilocalories per exercise session (1230 kJ).
Peter currently weighs 110 kg and has a goal weight of 99 kg for a total weight loss of 11 kg.
If Peter exercises 5 days per week for 60 minutes at a heart rate range of 137–147 beats per minute he will expend 294 kilocalories per 60 minute session x 5 sessions per week = 1470 kilocalories per week (6,154 kJ)
In order for Peter to lose I kg of body weight he would need to expend 7,700 kilocalories.
Peter ‘s goal is to lose 11 kilograms or expend 84,700 kilocalories (354,638 kJ).
How long will it take Peter to reach his goal body weight?
If Peter expends 1470 kilocalories per week it will take him (84,770) = 57 weeks to lose 11 kilograms if he maintained his present eating habits.
This tells us that the one hour per day five days per week that Peter is exercising at the gym is not producing the rapid weight loss that we have been told exercise will create. If Peter does not supplement his exercise program with additional daily movement there is a possibility that if all things do not remain equal he could put weight back on.
It is becoming much clearer that weight loss is a long process that requires a behavioural change as well as change in mind set where we are required to move at light to moderate intensity throughout our day at home, at work, during leisure times and while transporting. We can never underestimate the importance of what we eat and how much we eat!
Simply by adding daily active lifestyle movements Peter could potentially expend another 500 Kcals of energy expenditure per day, which is over 200 Kcals more than the formal exercise session produced.
If Peter (classified as obese) was exposed to a high intensity exercise session before he was prepared for it, he would still only expend less than 500 Kcals per session. He would also then be potentially exposed to joint and muscle injuries, over production of free radicals, inhibition of nitric oxide in the blood vessels and other overuse or overtraining symptoms.
What do you think the answer is?
Dr Paul Batman is Director Education at Australian College. Australian College is one of Australia’s leading accredited online colleges.