The group of age of 21 - 30 has the maximal mean strength of 12.6 pounds, group 31 - 40: 12, 6 pounds, group 41 - 50: 12 pounds, group 51 - 60: 11.7 pound; group 61 - 70: 10.1 pounds; 71 years old and more: 7.9 pounds.