OBJECTIVES
During walking, ground irregularities and surface hardness can alter gait characteristics and increase walking energy demands. According to prior research, a surface that is more irregular and softer increases stride variability and energy expenditure. Walking on sand requires between 1.6 and 2.5 times more mechanical work (foot movement) and 2.1 to 2.7 times more energy than walking on a hard surface. Moreover, sand has specific properties that the hardness of sandy surfaces can vary depending on their moisture content such as wet sand at the beach. Despite these characteristics of sand, it is unknown to what extent the energy metabolism, including energy expenditure and energy system distribution, differs during walking based on the moisture content of the sand. Therefore, we aimed to determine alteration in energy metabolism during walking on three distinct types of terrain (sidewalk, dry-, and wet sand) in obese and overweight individuals.
METHODS
This study was designed as a crossover randomized controlled trial. A total of 16 males (eight overweight and eight obese; mean age: 24.9 ± 2.3 years, mean body mass index: 28.1 ± 5.3 kg/m2) were recruited for this study. Using the body mass index for Asian-Pacific individuals, we classified overweight (≥ 23 kg/m2 and < 25 kg/m2) and obese (≥ 25 kg/m2) individuals. On the first visit to the laboratory, participants performed the resting metabolic rate test for 10 minutes. All participants performed three sessions of 25-min walking test (walking for 15 minutes and recovery for 10 minutes) with different types of terrain (sidewalk, dry, and wet sand). For the walking test, we measured oxygen consumption (VO2) with a portable gas-exchange analyzer and muscle oxygen saturation (SmO2) of the vastus lateralis with a wireless near-infrared spectroscopy device. In addition, we monitored the heart rate in real-time using the chest heart rate monitor. Before and after the walking tests, blood lactate concentration was also measured. Then, we calculated the energy expenditure and percentages of three energy systems: aerobic, anaerobic lactic, and anaerobic alactic.
RESULTS
Walking on dry sand showed higher relative oxygen consumption (Relative VO2, ml/kg/min) and heart rate compared to walking on a sidewalk. The total energy expenditure was also higher on dry sand than on the sidewalk. In addition, dry sand walking showed a higher percentage of the aerobic energy system. The comparison of muscle oxygen saturation between sidewalk walking and dry sand walking is ongoing. The data during the wet sand walking are still being collected.
CONCLUSIONS
A higher amount of energy was expended during the dry sand walking test, with a greater contribution from the aerobic energy system. These findings suggest that even low-intensity exercises in sand, such as walking, can contribute to increased energy expenditure and metabolism in obese individuals. Additionally, exercising in sand may be advantageous in the development of exercise programs aimed at improving metabolic health and increasing energy expenditure in individuals with obesity.