Effect of an Unstable Shoe Construction on Lower Extremity Gait Characteristics Nigg, Benno M. Ferber, Reed Gormley Tim Human Performance Laboratory University of Calgary Calgary Canada

Theoretical Concept Strengthening muscles close to the movement axis substantially reduces joint loading Reduced joint loading reduces lower extremity pain

Methods 8 subjects (5 male,3 female) Age years Mass kg Height cm All free from lower extremity injury or pain None had used MBT previously

Testing Procedure Test 1 Three trials of 30 seconds each to determine the centre of pressure and the corresponding muscle activation during quiet standing Three trials of 30 seconds each to determine the centre of pressure and the corresponding muscle activation during quiet standing In the control shoe ( Adidas Supernova) mass 358g and the black casual MBT mass 650g

Test 2 10 walking trials on a treadmill initially in the Adidas then in the MBT Walking speed km/h Measured parameters were ;lower leg kinematics and kinetics,selected soft tissue vibrations and selected EMG data (tibialis anterior,medial gastrocnemius,biceps femoris,vastus medialis and gluteus medius)

Test 2 B Subjects then wore the MBTs for hours per day for the next two weeks and then had Test 2 repeated, the same parameters being measured. Oxygen consumption testing was also carried out at this stage

Kinematic and Kinetic Data Kinematic data – 8 high speed video camera system (MAC) Kinetic data collected simultaneously using a Kistler force plate Peak joint angle,peak GRF values and rotational impulse to each joint determined for the first and second half of the stance phase for each condition and trial

EMG data Bipolar surface electrodes placed midway between motor end plate and the distal myotendinous junction Frequency bands set to correspond to slow and fast motor unit activation Total,low and high intensities were averaged over the 30 second quiet standing period Total, low and high intensities were averaged over the pre-heel strike(100ms before heel strike) and post-heel strike(100ms after heel strike) interval in the walking tests

Soft tissue vibration Soft tissue vibrations were measured from the muscle bellies of the rectus femoris,long head of biceps femoris and lateral gastrocnemius. Using skin mounted tri-axial accelerometers

Oxygen consumption Testing After the 2 week accomodation period. same time of day Walking speed 5.0km/h Four 5 minute walks with a 3 minute rest interval in between each walk to change shoes Repeated on day 2 2 protocols used U-C-C-U or C-U-U-C Each participant followed both protocols

STUDY RESULTS GO TO ADOBE DOCUMENT!

Discussion …………. Sample size WAS sufficient for this study Centre of pressure excursions larger for the MBT than the Adidas in quiet standing Muscle activity to provide this stability changed between Test1 and Test2 In MBTs initially both an ankle and a hip strategy were incorporated to maintain quiet standing ………………….

In the restest there was less activation of gluteus medius and more activation of medial gastocnemius,biceps femoris and vastus medialis. Indicating recruitment of other ankle and knee stabilisers during quiet standing.In effect the MBT CAN BE EFFECTIVELY USED FOR STABILITY TRAINING

If the skeleton has a preferred movement path for a given movement task then it follows that joint moments and or muscle activity should be altered to maintain that preferred movement path. If a shoe attempts to produce a movement that counteracts this preferred movement path then muscle activity or joint moments are increased. If however the muscle activity or joint moments are decreased then one can assume that the shoe approaches the preferred movement path of the joint more closely

In the knee there was a decrease in all three moments measured and in the hip there was a decrease in two of the three moments measured. Thus it can be concluded that THE MBT SHOE PRODUCED A MOVEMENT FOR THE HIP AND KNEE JOINT WHICH WAS CLOSER TO THE PREFFERED MOVEMENT PATH THEN THE ADIDAS SHOE. THIS CORRESPONDS TO A REDUCTION OF HIP AND KNEE LOADING DURING WALKING

Nigg et al have proposed that muscles are tuned to minimise soft tissue vibrations. This is achieved by keeping the vibration amplitude constant and changing the vibration frequency if necessary. This was the case with MBT shoes especially in the biceps femoris and gastrocnemius muscle groups.

Walking in MBT footwear required a 2.5% increase in oxygen consumption with an unchanged heart rate. In walking muscle activity did not change significantly other than a reduction in the tib. Ant and biceps femoris activity The difference in oxygen consumption was primarily thought to be due to the mass difference of the shoes- 292 g. Subjects using the MBT shoe will therefore use more energy in their exercise programmes