The present study examined the activity profile, heart rate and metabolic response of small-sided football games for untrained males (UM, n=26) and females (UF, n=21) and investigated the influence of the number of players (UM: 1v1, 3v3, 7v7; UF: 2v2, 4v4 and 7v7). Moreover, heart rate response to small-sided games was studied for children aged 9 and 12 years (C9+C12, n=75), as well as homeless (HM, n=15), middle-aged (MM, n=9) and elderly (EM, n=11) men. During 7v7, muscle glycogen decreased more for UM than UF (28 +/- 6 vs 11 +/- 5%; P<0.05) and lactate increased more (18.4 +/- 3.6 vs 10.8 +/- 2.1 mmol kg(-1) d.w.; P<0.05). For UM, glycogen decreased in all fiber types and blood lactate, glucose and plasma FFA was elevated (P<0.05). The mean heart rate (HR(mean)) and time >90% of HR(max) ranged from 147 +/- 4 (EM) to 162 +/- 2 (UM) b.p.m. and 10.8 +/- 1.5 (UF) to 47.8 +/- 5.8% (EM). Time >90% of HR(max) (UM: 16-17%; UF: 8-13%) and time spent with high speed running (4.1-5.1%) was similar for training with 2-14 players, but more high-intensity runs were performed with few players (UM 1v1: 140 +/- 17; UM 7v7: 97 +/- 5; P<0.05): Small-sided games were shown to elucidate high heart rates for all player groups, independently of age, sex, social background and number of players, and a high number of intense actions both for men and women. Thus, small-sided football games appear to have the potential to create physiological adaptations and improve performance with regular training for a variety of study groups.