RETROGRADE TRAINING

TABLE 2: SUMMARY OF INCREASE IN MUSCLE ACTIVITY DURING BACKWARD GAIT AS A % OF FORWARD WALKING (2)

Gluteus maximus Rectus femoris Vastus medialis Vastus lateralis Biceps femoris Semitendinosis Gastrocnemius

(lateral head) Tibialis anterior

94% 220% 245%

135-181% 107-170% 94% 40%

154%

was different from forward walking. They reported that backward walking was asso- ciated with an increased cadence and decreased stride length when compared with forward walking, however the relative times were similar to forward walking. These authors also observed that the joint kinematics involved in backward walking were substantially different to forward walking.

A more extensive investigation by Grasso (2) looked at the motor patterns for back- ward versus forward locomotion. The study concluded that the relationship among gait cycle, step length and speed have the same shape irrespective of gait direction at a given speed greater than 2.5km/h, although the cadence of backward gait tends to be faster and the step length tends to be shorter than forward gait.

This research shows us that although there may be some differences between the two forms of walking that from a kinematic point of view BW is a simple reversal of FW. Therefore it is important to look at other parameters to determine where the proposed benefits of BW come from.

Electromyography The electromyographic (EMG) activity mean of selected lower extremity muscle groups during forward and backward gait has been investigated in various studies (3,4,7,8,9). Findings have shown that muscle activity increases exponentially with speed in both backward and forward walking gait. At each given speed however, EMG activity generally tends to be higher in backward walking gait than forward walking gait.

The tables 2 and 3 summarise muscle activ- ity during backward gait on a level surface and inclined surface as a percentage of muscle activity during forward walking.

Clearly muscle activity is different between forwards and backwards walking. However insufficient research of a rigorous standard has been carried out to confi- dently determine the relationship between muscles in FW and BW, or the magnitude of this difference.

Vertical ground reaction forces Another aspect of the research that is important is the joint loading, as propo- nents of BW suggest that one of the main reasons that it is beneficial in a wide range of rehabilitation is reduced loading of the lower limb. Threlkeld (10) carried out a study which investigated both vertical ground reaction forces and vertical impulse (the area under the vertical ground reaction force time curve between foot strike and the onset of the peak force) during forward and backward run- ning. The forward running group had a mean vertical ground reaction force maxi- mum of 2.695 ± 0.189 times bodyweight. The backward running group had a mean vertical ground reaction force maximum of 2.545 ± 0.155 times bodyweight. The for- ward running group had a mean vertical impulse of 0.206 ± 0.016 bodyweight/

TABLE 3: EMG ACTIVITY DURING STANCE PHASE OF GAIT AS A % OF FORWARD WALKING (9)

Speed (mph) Muscle Rectus femoris Biceps femoris

Incline 0% 5%

10% 0% 5%

10% www.sportex.net Incline (%)

Initial contact 164% 152% 163% 71% 64% 62%

Sets

STANCE PHASE OF GAIT Mid-stance 26% 29% 31% 44% 31% 29%

second, however the backward running group had a mean vertical impulse of 0.157 ± 0.015 bodyweight/second. Both the vertical ground reaction force maxi- mum and vertical impulse were significant- ly less during backward running than for- ward running.

Cardiovascular demands One of the challenges that face clinicians is to maintain a patient’s fitness while allowing injured tissues to heal. However recognised safe forms of exercise such as cycling do not always produce sufficient cardiovascular demands to maintain com- petitive levels of fitness.

Chaloupka (11) compared FW versus BW and found that: 1) At a given elevation, backward walking elicited greater cardiorespiratory, metabol- ic, and perceptual responses than forward walking

2) Backward walking at 5% elevation could provide a sufficient stimulus to maintain cardiorespiratory fitness

Flynn et al (12) carried out a similar study and their results showed that VO2, HR, and blood lactate were significantly higher during backward walking and running than during forward walking and running. Therefore they concluded that for a given speed, backward locomotion elicits a greater metabolic demand and cardiopul- monary response than forward locomotion.

In general, these studies suggest that while undergoing rehabilitation, an injured athlete may continue to exercise using backward walking/running at an intensity sufficient enough to maintain cardiovascular fitness levels.

Rest (secs)

Heel-off 31% 31% 40% 84% 84% 78%

IMPLICATIONS Although some of the research presented above is not entirely conclusive, it is pos- sible to apply some of the findings to clin- ical practice in terms of management of specific conditions and management at certain stages.

Patellofemoral pain syndrome It is well known that one common treat- ment approach in the management of patellofemoral pain syndrome is to decrease patellofemoral joint forces so that load-elicited pain and damage to car- tilage are minimised. One study has been reported in which attempts have been

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