Ground reaction forces and osteogenic index of the sport of cyclocross

Abstract

Weight-bearing activity has been shown to increase bone mineral density. Our purpose was to measure vertical ground reaction forces (GRFs) during cyclocross-specific activities and compute their osteogenic index (OI). Twenty-five healthy cyclocross athletes participated. GRF was measured using pressure-sensitive insoles during seated and standing cycling and four cyclocross-specific activities: barrier flat, barrier uphill, uphill run-up, downhill run-up. Peak and mean GRF values, according to bodyweight, were determined for each activity. OI was computed using peak GRF and number of loading cycles. GRF and OI were compared across activities using repeated-measures ANOVA. Number of loading cycles per activity was 6(1) for barrier flat, 8(1) barrier uphill, 7(1) uphill run-up, 12(3) downhill run-up. All activities had significantly (P < 0.01) higher peak GRF, mean GRF values and OI when compared to both seated and standing cycling. The barrier flat condition (P < 0.01) had highest peak (2.9 times bodyweight) and mean GRF values (2.3 times bodyweight). Downhill run-up (P < 0.01) had the highest OI (6.5). GRF generated during the barrier flat activity is similar in magnitude to reported GRFs during running and hopping. Because cyclocross involves weight bearing components, it may be more beneficial to bone health than seated road cycling.

Keywords: bone health; cycling; loading cycles; osteogenic; physical activity.

Figure 1

Cyclocross racer completing a barrier flat activity, which involves dismounting on flat ground, jumping over two barriers, then remounting the bike.

Figure 2

Graphical depiction of loading cycles and accompanying forces generated during a representative barrier flat trial. The relatively stationary force indicates the time when the rider is preparing for dismount, followed by a distinctive absence of force prior to the first impact as the rider dismounts the bicycle. The rider then performs a series of loading cycles followed by remounting and resumption of seated cycling.

Figure 3

A comparison of peak vertical GRF values for seated cycling, standing sprint cycling and cyclocross-specific activities with data from literature-derived values. Note: ^★ From Groothausen et al. (1997) and Weeks and Beck (2008).

Figure 4

A comparison of the calculated OI of cyclocross activities with the calculated OI of other repetitive and weight-bearing activities. Notes: ¹120 rpm, GRF 1.6 BW. ²15 barrier flat activities. ³Lower extremity exercises, 3 sets of 3–12 reps against variable resistance, Lester et al. (2009). ⁴90 rpm, GRF 0.8 BW, Weeks and Beck (2008). ⁵80 steps/min (40 per leg), GRF 1.1 BW, Turner and Robling (2003). ⁶2 sets of 10 jumps against 80% BW resistance, Erickson and Vukovich (2010). ⁷Bailey and Brooke-Wavell (2008). ⁸Santos-Rocha et al. (2006). ⁹Against body weight only, GRF 3 BW, Turner and Robling (2003). ¹⁰160 steps/min (80 per leg), GRF 2.6 BW, Weeks and Beck (2008).