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A STUDY OF IMPACT SHOCK DURING JOGGING
A comparison between conventional running shoes and Kangoo Jumps. (This is only a summary of the whole study)

Swiss Federation Institute of Technology

Clinical Department of Orthopedic & Traumatology, Division of Sports Medicin
G. Gremion, P.F. Leyvraz, E. Mercier, K. Aminian.

ABSTRACT
Impact force experienced during running has been recognized as a source of injury. Much less is known about impact injury during the use of Kangoo Jumps, a revolution in shoe design, which includes a leaf spring attached to the sole of the shoe.

The purpose of this study was to investigate the impact characteristics for Kangoo Jumps and to test the hypothesis that there is lower impact shock while using Kangoo Jumps than running in conventional athletic shoes. Eleven (11) athletes, six (6) males and five (5) female subjects participated in the study. Each completed two different trials with low-mass accelerometers attached to the proximal tibia and to the lumbar spine (L5). Each performed three trials of vertical jumping and a trial of running for 20 seconds at a self-pace, wearing his or her normal training shoes and then Kangoo Jumps.

Our results showed that using Kangoo Jumps exhibited a significant reduction of impact force during running. We observed an acceleration of 7g at the tibia and 2.5g at the lumbar spine with conventional training shoes. With Kangoo Jumps the acceleration impact force was only 3.5g at the tibia and 1.9g at the lumbar spine.

This study concluded that using Kangoo Jumps while running results in less impact shock to the body with each foot contact and may be a useful exercise modality for rehabilitation of sports related injuries due to the reduced impact shock.

INTRODUCTION
Walking and running are well known exercises that can improve cardiovascular endurance, strengthen muscles and reduce body fat. Under normal circumstances of running or jumping, the elastic compliance of the internal structure of the foot, such as the internal arch and tendons, reduce impact forces and provide only about 40% to 60% energy return.

One aspect of running which has been well-documented is the impact shock transmitted through the body when the foot makes contact with the ground. This event occurs about 6,000 times in a race of 10 km. The shock wave is transmitted across the structures of the lower extremity and upward through the spine to the head.

One positive aspect of the shock is to stimulate the bone mass density of the lower extremities. However repetitive landings and impacts have also been implicated in degenerative diseases for the knees and the hips.

With injuries, it seems to be important to restore the full ability to compete using different methods which diminish joint loading without diminishing the capacity to improve the cardiovascular endurance.

Recently, there has been a fitness shoe system developed, providing an enjoyable method of highly effective exercise that would appear to significantly reduce the impact of high acceleration forces. The shoe, Kangoo Jumps, is constructed in a similar fashion to that of an inline roller skate with the exception of wheels. Under the shoe is an elliptical arch stretching from the toe to the heel of the shoe that is bisected with a removable band. At each step, we observe a depression of the arch that works like a leaf spring, returning to its previous form.

The purpose of this study was to examine impact shock and the attenuation characteristics during the use of Kangoo Jumps while running. To that end, we have measured impact force at the tibia and lumbar spine during the use of Kangoo Jumps while running and then we compared these results with data collected from the same subjects while running with conventional running or training shoes.

METHODS
Eleven healthy subjects (mean +/- SD age 31 +/- 7 yr; height 176+/- 11 cm; mass: 64.6 =/- 9 kg.), 6 males and 5 females volunteered to take part in the study. They were sport teachers in fitness centers and none reported any significant musculo-skeletal disorder. All subjects were previously trained in the correct use of Kangoo Jumps.

The time domain variables output for statistical analysis were PA tibia and PA lumbar spine. The main effect of condition for these dependent variables was tested using a subject, repeated-measures ANOVA.

RESULTS
During running we observed a significantly lower peak impact for Kangoo Jumps (P=0.001). Mean PA tibia value for the Kangoo running condition was 4 G, the mean spine value, 2.5 G whereas running with normal training shoes showed higher values of force acceleration: 7.8 G PA tibial and 2.3 PA spine.

The length of the step measured by the time in air is greater with Kangoo Jumps: 143 cm with Kangoo Jumps, 123 with training shoes.

Exemplar timer series of tibial and lumbar spine acceleration signals during stance phase of running and Kangoo jumping. PA indicates peak acceleration just after foot contact.

DISCUSSION
The purpose of this study was to investigate the peak acceleration force characteristics when jogging in a pair of Kangoo Jumps compared to normal training shoes. The results clearly show that the Kangoo Jumps result in considerably less impact forces being transferred to the lower limbs compared to normal training shoes. In particular, the impulse during first initial contact with the ground is reduced some 50% . Furthermore, the length of the step measured by the time in the air is greater with Kangoo jumps than with training shoes. This is a valuable contribution to attenuate the frequencies of impacts of the lower limb with the ground for the same intensity of the physical work.

The frequency analysis of tibial and lumbar spine acceleration showed that using Kangoo Jumps demonstrated less impact acceleration, with lower values than running with training shoes for peak and median frequency.

The frequency range is associated with the collision of the foot to the ground and this frequency band may be implicated in musculo-skeletal injuries. Some have suggested that removal of higher frequencies may reduce the likelihood of degenerative joint diseases. Kangoo Jumps may, therefore, prove to be an aerobic exercise workout that is less harmful to the joints in terms of repetitive impacts of the foot and ground.

The results of the frequency analysis for the running trials agree with other studies. The running condition with training shoes displayed peaks between 6 and 10 g at the tibia level as found in previous studies. With Kangoo Jumps acceleration is 50% lower. The reduction of the force impact is significant.

The curves below demonstrate the force of impact on the legs, hips and spine while running, as measured with a piezoresistive accelerometer.