Preferred walking speed on rough terrain: is it all about energetics?

Area of Science:

• Biomechanics
• Human locomotion
• Energy expenditure

Background:

• Humans typically walk at speeds minimizing metabolic energy expenditure per unit distance (cost of transport, COT).
• Previous studies on preferred walking speeds were mainly conducted on smooth, level surfaces or treadmills.
• The objective function for preferred walking speed may be more complex than solely minimizing COT.

Purpose of the Study:

• To investigate if the objective function for preferred walking speed differs between smooth and rough terrain.
• To compare preferred walking speeds with speeds that minimize COT on both surfaces.
• To determine the influence of terrain complexity on the energy cost of transport and speed preference.

Main Methods:

• Ten healthy men walked on a smooth, level floor and a rough, natural terrain trail.
• Participants completed trials at various speeds relative to their preferred speed on each surface.
• Cost of transport (COT) and preferred walking speeds were measured and analyzed.

Main Results:

• COT values were significantly higher (approx. 115%) on rough terrain compared to smooth terrain.
• On smooth surfaces, preferred speed was not statistically different from the speed minimizing COT.
• On rough terrain, preferred speed was significantly slower than the speed minimizing COT (P=0.02).

Conclusions:

• The objective function for preferred walking speed on rough terrain likely includes factors beyond minimizing COT, such as stability.
• Terrain complexity influences the trade-off between energy efficiency and other locomotor goals.
• Humans adjust their walking strategy on uneven surfaces to balance energy cost and stability.