Running economy of elite surf iron men and male runners, on soft dry beach sand and grass.

The primary aim of this study was to measure the energetics of six elite surf iron men (who participate in regular sand running training), performing steady-state running trials on grass in shoes at 8, 11 and 14 km x h(-1), and on sand bare foot and in shoes, at both 8 and 11 km x h(-1). The net total energy cost (EC, J x kg(-1) x m(-1)) was determined from the net steady-state oxygen consumption and respiratory exchange ratio (net aerobic EC) plus net lactate accumulation (net anaerobic EC). For the sand barefoot and sand in shoes running trials at 8 and 11 km x h(-1), net aerobic EC and total net EC (but not anaerobic EC) were significantly greater (P < 0.001) than the grass running trial values. No differences (P > 0.05) existed between the sand barefoot and sand in shoes trials. These measures were compared with data obtained from eight well-trained male recreational runners who performed the same protocol in a previous study, but who were not accustomed to running on sand. Comparisons of net aerobic EC between the two groups for the surface conditions were not significantly different (P > 0.05). For net anaerobic EC, the iron man values were significantly less (P < 0.02) than the recreational runner values. For net total EC, the iron man values were less than the recreational runner values, but the differences were only significant when both groups ran on sand barefoot (P < 0.03: on grass P = 0.158; on sand in shoes P = 0.103). The lower lactate accumulation values recorded for the iron men on both grass and sand may indicate that running on sand potentially reduces metabolic fatigue when running on firm or soft surfaces.