I’ve gotten involved with the Global Corporate Challenge at work and the basic premise is that you wear a pedometer around everywhere and monitor how many steps you take on a daily basis. The benchmark figure is 10,000 steps per day. Teams are formed and there’s some kind of website thing and I don’t really have the time to go into it all… The point is, it’s a thing and I’m in it.
My problem is that I lift weights for 3 hours after work on Monday, Tuesday and Friday, after which I go home, eat and sleep. Spending 4 hours at Tafe on Thursdays doesn’t leave much time then, either. My step count is obviously extremely low. I’ve decided to calculate how much energy I’m expending in each training session since I record everything I do on my program, in order to convert into steps so I won’t hold my teammates back so much. Here’s my process:
Using a 75kg snatch as a sample calculation, I need to know what amount of potential energy I put into the bar, as well as my own body. So I split the movement into parts.
Movement 1 is pulling the weight from the floor to the top of the “second” pull. Using my competition photo, I can see that in a full snatch, I’ll pull the bar from the floor (Olympic plates are 450mm in diameter, so bar centre is at 225mm) to about nipple height, which is about 1450mm. This gives a change from 1225mm. At 75kg, this is Ep=mgh=75 kg * 9.81 ms^-2 * 1.225 m=901 Joules.
I ignore the energy I expend buy jumping under the bar. Movement 2 for a full snatch is overhead squatting from rock bottom snatch position to the finish position. This is a height change from 1140mm to 1880mm, a delta of 740mm. Calculating in the same fashion as above, I get an energy input of 544 Joules.
This is not the total amount of energy in the lift. I haven’t accounted for the effort required to raise my own bodyweight. In order to do this, I needed to calculate the rough position of my own centre of gravity. I did this by finding my balance point on a chair with a highly complicated and technical procedure I like to call “supermanning.” With my hands by my side, my COG is about ass-height. With my arms overhead, it raises up to about the small of my back.
Calculating the energy input for movement 1 and 2 of a full snatch as above, but with modified height changes, the energy inputs are 418 Joules and 539 Joules. This can all be added together to arrive at a sum energy input of 2403 Joules for a 75kg full snatch, assuming the snatcher to weigh 82kg. A clean and jerk can be calculated the same as above, except there’s an extra movement- the jerk. Assistance exercises are mostly just part of the above calculations.
Entering all this into a spreadsheet, I found my last workout to have been about 127 KiloJoules of work done. This is
a fairly an extremely conservative estimate, as it only considers actual work input into the bar- 100% efficiency. According to EXTERNAL, INTERNAL AND TOTAL WORK IN HUMAN LOCOMOTION by P. A. WILLEMS, G. A. CAVAGNA AND N. C. HEGLUND, 16 September 1994, as well as a few other random sources on the internet, the efficiency of human muscle is generally about 25%, so I can safely multiply out the energy by a factor of 4 to get energy input, rather than output. Further, as mentioned by a scientist and weightlifter in the comments below, I should look into the energy required to hold the weight as well as lift it… I’ll look into this later after I’ve spoken to him in-depth.
All that remains now is to go for a walk tomorrow for a predetermined distance in order to find how many steps I take per kilometer travelled. Then I’ll convert this 127 KiloJoules into X “Effective Steps” based on how much energy an average male expends walking one kilometer.
Update: I’ve done this using google maps and my pedometer. My stride is about 0.787 metres on average. At the moment, I have a conservative estimate that my last workout was worth about 3,000 steps. At the moment, I think this is still far too conservative, as I went for a 6,000 step walk today and feel normal, whereas after training, I’m tired, weak and lethargic. I expect the number to significantly increase as I refine the way I calculate this. Hopefully I’ll stumble upon some research based numbers, which would be far superior to potential energy calculations…