Holding 5 lb weights in each hand while on treadmill

If you're relying on the treadmill to calculate calories burned, make sure the starting weight is 10 pounds higher?

I think it is ankle weights that are the issue while walking, but I would have to look into it to be sure.

On the cal question, the best way to figure the difference in cals burned would be to use a HRM with the weights one day then without another.
You could also look for cals burned on line entering in your info (hieght, weight etc) then enter the same exercise with you weighing 10lbs more. This will not be accurate but will at least give you some extra cals for doing this. I would assume that you would burn a little more as you will be moving the weights but this is better than nothing.

If you're relying on a HR monitor, remember that (as far as I know) the only HR monitor that currently calculates calories based on your actual (real time, during exercise) calories burned based on your HR is the Garmin 310XT. All of the other ones are based on a logorhythm that estimates the calorie burned based on age/sex/weight.

If you want to really calculate it (Yep, I'm a geek!), here is how we trainers do it. Note: (1) "Net Calorie Burn" measures calories burned, MINUS basal metabolism. (2) The walking formulas apply to speeds of 3 to 4 mph. (3) At 5 mph and faster, walking burns more calories than running (because walking THAT fast is more work than jogging the same speed ... and looks pretty interesting too! LOL).

RUNNING
Your Total Calorie Burn/Mile: .75 x your weight (in lbs.)
Your Net Calorie Burn/Mile: .63 x your weight

WALKING
Total Calorie burn/mile: .53 x your weight
NET calorie burn/mile: .30 x your weight

EXAMPLE CALCULATION of walking with and without 10 pounds in additional weight (randomly chosen 180 pound weight):
.3 x 180 = 54 calories per mile
.3 x 190 = 57 calories per mile

EXAMPLE CALCULATION of running with and without 10 pounds in additional weight (randomly chosen 180 pound weight):
.63 x 180 = 113.4 calories per mile
.63 x 190 = 119.7 calories per mile

I used NET calories because the other (total) incorporates how many calories your body is burning (non exercise related). Adding in those extra non-exercise calories would double count since your basic daily rate does consider the basic body's calorie needs for a 24 hour period. Whoa .. hope that didn't complicate things!

If I didn't explain this well, let me know and I'll try again!

Long story short, it makes a difference due to your basically supporting a heavier weight during exercise (the extra 10 pounds), but the extent to which it makes a difference, depends upon the level of exertion (e.g., walking versus running).

Holding weights while walking has little effect--on either cardio training or strength. Studies done on this subject have shown that a vigorous arm swing can have a significant effect.

Adding weight to the arm swing increased the effect somewhat, but, percentage-wise, not as much as the arm swing itself (unless you went up to 10lb dumbbells, which is not practical).

Carrying hand weights---don't bother, doesn't really do anything.

Swinging arms---can improve exertion/calorie expenditure by a notable amount; amplitude of swing must reach shoulder height in front to have effect.

Swinging arms w/weights (1-5lb): Adds incrementally to effect of swinging arms unweighted (obviously, 1lb effect is marginal, 5lb effect more substantial, but still most of the effect comes from the arm swing itself, not the weight).

Okay, so I wanted hold 5 lb weights in each hand while on the treadmill, and before I got on I wanted to see how many more calories this would burn rather than just the treadmill without the weights. I can't figure out how to log this in to the exercise log. Does anyone know how I would log this in and how many more calories it would burn if I were to jog at 4.5mph with the weights for 30 mins?

Well, you're actually "carrying" an extra 10lbs of weight on your body so you may just want to bump the speed up 1 mile.