A new study by Dutch researchers has stated that there is a metabolic threshold that occurs in young adulthood, at which long-term daily physical activity becomes deleterious for lumbar bone mineral density (LBMD) after peak bone mass is reached. The researchers, over a 10-year period, investigated the longitudinal relationship between daily physical activity and LBMD in 225 men and 241 women. They assessed LMBD, habitual daily physical activity, total body weight and calcium intake at the mean ages of 27, 32 and/or 36 years. Mechanical and metabolic components of physical activity were analysed. The mechanical aspect covered the sum of all ground reaction forces in physical exercise (MECHPA). The metabolic aspect involved a weighted metabolic score for intensity, frequency and duration of physical exercise (METPA). The researchers found that the metabolic aspects of physical activity became ineffective for LBMD at the threshold point. However, physical activity causing mechanical loading on the skeleton had a small positive influence on LMBD in males aged from 27 to 36 years old. The researchers concluded that MECHPA was a significant positive linear predictor of LMBD for men but not for women.