Energy
Energy and Thermal Physics

## Energy and exercise

Stories from Physics for 11-14 14-16

• During a marathon, a typical runner transfers around 100 J during each foot strike with the ground, of which around 35 J is transferred to the elastic store of the Achilles tendon. A good running track can return an additional 12 J per step and increase running speeds by approximately 2%. Running tracks are designed to have a natural frequency of around 2 Hz to maximise energy transfer.
• Much of the energetic benefit of swimming for losing weight may be due to thermal transfer from the body rather than the work done in moving the body forward. An estimate of the energy transferred by a 65 kg swimmer in a pool at 27°C concluded that around 2 kJ/min of work is done propelling the swimmer forwards but ten times that amount, about 20 kJ/min, will be thermally conducted from the body. The author of the paper concludes, “This fact can be utilised by overweight persons to burn their extra fats [sic] even by just sitting in the water with their head above the surface.”
• By modelling the human body as a series of segments, a group of students calculated that the energy transferred by the upward motion of a press-up is around 342 J for the average male.

### References

Energy and Exercise
I. P. Herman, Physics of the Human Body, Berlin, Springer, 2007, p. 128
W. A. Sparrow, Energetics of Human Activity, Champaign, IL, Human Kinetics, 2000, p. 150
D. C. Agrawal, Work and heat expenditure during swimming. Physics Education, vol. 34, no. 4, 1999, 220-226, p. 224
O. Youle, K. Raymer, B. Jordan, & T. Morris, Drop and give me ten. Physics Special Topics, vol. 12, no. 1 2013, pp. 1-2

###### Energy
appears in the relation ΔEΔt>ℏ/2 ΔQ=mcΔθ E=hf E ∝ A^2
has the special case Photon Energy
is used in analyses relating to Emission/Absorption Spectra Phase Change