Energy expenditure of walking on a field tracks versus treadmill 1

Introduction

The physiological demands of walking have not yet been studied in a systematized manner in field situation. At present, almost all studies studied walking in laboratorial simulated situations. The aim of this study was to analyse the energy cost of walking in field compared to walking on a treadmill, for the same speed and gradient.

Methods

The measured variables were: oxygen consumption (VO2), energy expenditure (EE), heart rate (HR), weight (W) and height (H). The sample included 8 healthy male subjects (age 22,57±2,07yr; weight 69,71±7,76Kg; height 1,75±0,10m). The subjects did not practice walking regularly. The subjects completed 3 segments of natural pedestrian mountain paths with gradient and length of, respectively: 0% and 821m; 6% and 618m; 14% and 598m. The segments’ length allowed a VO2 stabilization and the subjects auto-selected their walking speed. The pedestrian paths selected are located in the Natural Park of Serra d’Aire e Candeeiros – Portugal, and are characterized as forest paths. The segments selection respected a gradient variability minor than 1% through all segments’ distance. The planimetry and altimetry was done by a topography technician with a total Sokkia station 130R (Sokkia, Casagiove, Italy). The VO2, HR and EE were taken with direct oximetria using a Cosmed K4b2 (Cosmed S.R.I., Rome, Italy) portable metabolic measurement system, and the W and H with a SECA (SECA, Germany, Hamburg). The laboratory replication of segments’ speed, length and gradient were performed in a treadmill by Technogym RunRace (Tecnogym, Gambottela, Italy).

Results

At 0%, 6% and 14% gradients the field vs treadmill VO2 measures were, respectively, 17,84±2,57 vs 23,43±2,35, 36,80±9,11 vs 33,06±3,83, 39,28±2,78 vs 44,09±2,46 ml.Kg-1.min- 1. Field versus treadmill significant differences (p?0,01) were identified for VO2, in segments with 0% and 14% gradient. The differences were, respectively, -5,59 (95%CI from -6,79 to – 4,40,) and -4,81 (95%IC from -7,9 to -2,53).. The HR was higher on the treadmill than on field walking in all exercise gradients, (101,05±11,11 vs 103,10, 125,38±14,24 vs 118,38±12,60, 137,81±10,74 vs 143,48±12,23 bpm, respectively for 0%, 6% and 14% gradients). No significant differences in HR were found between 0% and 6% gradient in both conditions. The EE was (field vs treadmill) , 6,85±1,98 vs 7,89±1,36, 11,62±2,39 vs 11,14±2,19, 13,35±1,93 vs 14,90±2,44 Kcal.min-1 (for 0%, 6% and 14% gradient, respectively). The EE and speed at 0% gradient during field walking (5,13 ±0,75 MET’s; 1,62 ±0,16 m.s-1) are similar to values found in other field studies (Spelman et al, 1993; Johnson, Benjamin, Silverman, 2002; Ainslie et al, 2002).

Discussion/Conclusion

VO2, FC and EE increase with the increasing of gradient, in both exercise conditions. In all field-walking trials at different gradients the VO2 is according to the ACSM’s recommendations on the intensity of exercise. The difference of mean values of VO2 at 0% and 14% gradient (field vs treadmill), indicates that the EE was higher in the treadmill situation. The VO2 increase in treadmill walking is likely to occur due to a greater increase of a stability control demands. Considering the field versus treadmill comparisons for all variables (VO2, FC, EE), none of the measured values at the 3 gradients indicate that the metabolic responses are identical on the two exercise conditions. For more conclusive results about the behaviour of VO2 at different gradients, a larger sample is recommended.