Ma Be asked in USMA 18535: >On Sat, 02 Mar 2002 22:05:44 > Barbara and/or Bill Hooper wrote: >... >>Similarly, 55 kW means you use 55 kJ each second, so if you use energy at >>that rate for 15 minutes (which is 900 s), you find you have used >>55 000 kJ (or 55 MJ) of energy. That value can be related to the heat energy >>produced (measured in joules) or mechanical energy produced (in joules) or.. > >I'm glad Bill brought this up. I'd like someone here to help me >understand the relationship between the figure that treadmills/bicycle >exercising machines give us in W with energy we used (which, >unfortunately, is invariably reported in calories). > >Something simply is not making any sense to me. Yesterday I was >monitoring how my wife was doing in the bike machine and I'd say she was >spending an average of 120 W+ in her exercise routine. Upon checking the >calorie reading it was stating that she spent about 260 calories during >her 30-min session! Am I missing something here?... > >Note: Doing the calcs would give us the following: >120 W x 30 min x 60 s = 216 kJ =~ 52 Cal >This is intriguing because I know I usually spend about 2 MJ of energy per >half-hour of running I do on my treadmill at ~12.5 km/h speed.
Two factors come to me. 1) The meter on the bike machine was flattering. 2) Your figure of 120 W only took account of the mechanical power required, but neglected the heat power produced. Joseph B.Reid 17 Glebe Road West Toronto M5P 1C8 TEL. 416-486-6071
