Do shock absorbing insoles in recruits undertaking high levels of physical activity reduce lower limb injury? A randomized controlled trial.

OBJECTIVES: To assess the benefits, if any, of the use of shock absorbing insoles in reducing lower limb injury among Air Force recruits, and to assess the differences, if any, in the efficacy of two commonly available shock absorbing insoles.

DESIGN: Randomized controlled trial.

SETTING: RAF Halton, UK. Site of all basic training for RAF personnel.

PARTICIPANTS: 1205 recruits participating in basic training between 17 September 2003 and 7 April 2004.

INTERVENTIONS: Participants were randomized to receive either standard issue Saran non-shock absorbing insoles, or shock absorbing Sorbothane or Poron insoles, on a 1:1:1 basis.

MAIN OUTCOME MEASURES: The primary outcome measure was withdrawal from training for lower limb injury. The two primary comparisons were shock absorbing insole versus non-shock absorbing insole, and Sorbothane versus Poron (comparison of different shock absorbing insoles). Secondary outcomes were medical withdrawals for reasons other than those qualifying for the primary outcome measure.

RESULTS: When comparing the non-shock absorbing insole to the shock absorbing insoles 72/401 participants (18.0%) allocated to Saran insoles were removed from training because of a qualifying lower limb injury, compared with 149/804 (18.5%) allocated to the shock absorbing insole (Sorbothane or Poron), odds ratio 1.04 (95% CI 0.75 to 1.44; P=0.87). When comparing the two shock absorbing insole 73/421 participants (17.3%) randomized to Sorbothane were removed from training because of a qualifying lower limb injury, compared with 76/383 for Poron (19.8%), odds ratio 0.85 (95% CI 0.58 to 1.23; P=0.37).

CONCLUSIONS: Similar rates of lower limb injuries were observed for all insoles (shock absorbing and non-shock absorbing) in the trial. The trial provides no support for a change in policy to the use of shock absorbing insoles for military recruits.