The authors found a difference between W40 and W70 sessions for mean ( standard deviation ) ventilation ( 25.1 % [ 8 % ] and 32.1 % [ 9 % ] of maximal ventilation , respectively ; P = 0.04 ) and a small difference for mean ( standard deviation ) heart rate ( 73 [ 7 ] and 79 [ 8 ] beats/min , respectively ; P < 0.01 ) .