Extra! Extra! Read all about it! The list is getting its edge back!
> Bingo! > > You're balancing heat production, which is proportional to body mass, > against heat dissipation, which is proportional to surface area. Since mass > (volume) increases with the cube of the radius, and surface area only > increases with the square of the radius, it should be clear that weight (and > heat production) will increase faster than the heat dissipation properties > afforded by surface area. > > malmo > > http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui > ds=11211124&dopt=Abstract > > Advantages of smaller body mass during distance running in warm, humid > environments. > > Marino FE, Mbambo Z, Kortekaas E, Wilson G, Lambert MI, Noakes TD, Dennis > SC. > > Human Movement Studies Unit, Charles Sturt University, Bathurst, NSW, > Australia. [EMAIL PROTECTED] > > The purpose of this study was to examine the extent to which lighter runners > might be more advantaged than larger, heavier runners during prolonged > running in warm humid conditions. Sixteen highly trained runners with a > range of body masses (55-90 kg) ran on a motorised treadmill on three > separate occasions at 15, 25 or 35 degrees C, 60% relative humidity and 15 > km x h(-1) wind speed. The protocol consisted of a 30-min run at 70% peak > treadmill running speed (sub-max) followed by a self-paced 8-km performance > run. At the end of the submax and 8-km run, rectal temperature was higher at > 35 degrees C (39.5+/-0.4 degrees C, P<0.05) compared with 15 degrees C > (38.6+/-0.4 degrees C) and 25 degrees C (39.1+/-0.4 degrees C) conditions. > Time to complete the 8-km run at 35 degrees C was 30.4+/-2.9 min (P<0.05) > compared with 27.0+/-1.5 min at 15 degrees C and 27.4+/-1.5 min at 25 > degrees C. Heat storage determined from rectal and mean skin temperatures > was positively correlated with body mass (r=0.74, P<0.0008) at 35 degrees C > but only moderately correlated at 25 degrees C (r=0.50, P<0.04), whereas no > correlation was evident at 15 degrees C. Potential evaporation estimated > from sweat rates was positively associated with body mass (r=0.71, P<0.002) > at 35 degrees C. In addition, the decreased rate of heat production and mean > running speed during the 8-km performance run were significantly correlated > with body mass (r=-0.61, P<0.02 and r=-0.77, P<0.0004, respectively). It is > concluded that, compared to heavier runners, those with a lower body mass > have a distinct thermal advantage when running in conditions in which > heat-dissipation mechanisms are at their limit. Lighter runners produce and > store less heat at the same running speed; hence they can run faster or > further before reaching a limiting rectal temperature. > > PMID: 11211124 [PubMed - indexed for MEDLINE] > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Arthur Snoke > Sent: Thursday, August 26, 2004 12:19 PM > To: [EMAIL PROTECTED] > Subject: RE: t-and-f:the bigger they are, the harder they cool > > Yes, the mechanical work expended is proportional to the weight, so a > heavier runner expends more energy to run up a hill than does a lighter > runner. But that does not explain why the same runner, running at the same > pace on the same course (and with the same air resiatance and > friction) will suffer more if he/she is heavier when the temperature is 90F > compared to 40F. > > One reason is that weight is proportional to volume while heat loss is more > related to the surface area. Although body shape does not exactly scale > with weight, it is probably reasonable to say that in general heavier people > have relatively less surface area than lighter people so they cannot > dissipate heat as well. As the temperature increases, neat loss by both > conduction and by radiation is less efficient, then, for heavier people so > they are more likely to overheat. > > >
