Humans walk when going slowly and run to go fast, and switch between the gaits to use the one that is most efficient for the speed at which they are moving. In a bid to improve our efficiency even further, engineers have designed a range of different assistive devices worn around the legs – so-called exosuits, which take advantage of springs, clutches or electric motors – to reduce the energy required to walk or run. But usually, these assistive suits only benefit a single gait type, because the muscles in our legs activate in different patterns depending on whether we are walking or running. To overcome this limitation, a research team from Conor Walsh's lab at Harvard University, USA, set out to produce an assistive exosuit that could reduce energy expenditure during both walking and running by sensing the gait type that wearers used.
The team built a 5 kg suit to fit around a person's hips with cables running down the thighs from an electrical motor on the lower back. The motor shortens the cables to assist the hip muscles, such as the hamstrings and glutes, but responds differently depending on whether sensors embedded in the fabric detect the body is moving up–down – indicating walking – or down–up, when running. In a series of experiments, the team tested whether athletes save energy when wearing the suit, whether the suit can detect when athletes walk or run and whether the suit is versatile enough to provide energy savings across a wide range of walking and running conditions.
To test the effectiveness of the suit, the team recruited nine athletes to walk on a treadmill at 1.5 m s–1 and run at 2.5 m s–1 while measuring their energy use from their oxygen consumption. The suit reduced the energy cost of walking by 9.4% during assisted walking and by 4.0% while running – savings that should translate into improved athletic performance.
To show that the suit accurately detects when the person wearing it is walking or running, the team performed a series of tests involving treadmill walking and running, from speeds of 0.5 to 4.0 m s−1 while climbing up and down slopes, ranging from –10% downhill to 20% uphill. The suit did extremely well in almost all cases, correctly identifying the type of gait type used by the athlete on 99.98% of occasions. In addition, it was able to produce energy savings of up to 22.8% when the athletes were running at speeds ranging from 2.5 to 3.0 m s−1 on the flat and when walking uphill. The team also tested how well the suited volunteers coped when walking and running across different terrains, from normal ground to muddy tracks and snowy landscapes; the results indicate that the suit could benefit people in a wide range of challenging situations, such as firefighters and search-and-rescue teams, who often need to move fast while carrying heavy loads. The team also suggests that the suit may benefit patients, such as stroke victims, who require some support when struggling to walk during recovery.
