Background: The present study was undertaken to determine the effect of different uphill and downhill gradients on cardiorespiratory and metabolic responses of soldiers while carrying heavy military loads in two different modes.Methods: Eight physically fit male soldiers with a mean age 32.0±2.0 years

a mean height of 169.5±4.9 cm

and a mean weight of 63.8±8.4 kg volunteered for this study. Each volunteer completed treadmill walking trials at a speed of 3.5 km/h while carrying no external load

31.4 kg load in a distributed mode（existing load carriage ensembles） and compact mode（new back pack） over 5 different downhill and uphill gradients（–5%

–10%

0%

5%

10%） for 6 min at each gradient. During the walking trials

heart rate（HR）

oxygen uptake（VO

2

）

respiratory frequency（RF） and energy expenditure（EE） were determined by the process of breath-by-breath gas analysis using a K4 b2 system. The average of the last 2 min data from each 6 min walking trial for each individual was subjected to statistical analysis.Results: All parameters（HR

VO

2

RF

and EE） gradually increased with the change in gradient from downhill to level to uphill. The distributed mode showed higher values compared to compact mode for all gradients

e.g.

for VO

2

there was a 10.7

7.4

5.1

28.2 and 18.7% increase in the distributed mode across the 5 different gradients.Conclusions: It can be concluded from the present study that the compact mode of load carriage is more beneficial than the distributed mode in terms of cardiorespiratory responses while walking on downhill and uphill surfaces with a 31.4 kg load.