ACTIVITY OF LATISSIMUS-DORSI MUSCLE DURING INSPIRATORY THRESHOLD LOADS

The ability of the latissimus dorsi muscle OLD) to participate as an a ccessory inspiratory muscle has been the subject of controversy, Elect romyographic (EGM) activity of LD was evaluated in 11 healthy subjects (aged 30+/-2 yrs; forced expiratory volume in one second (FEV(1)) 106 +/-5% predicted; maximal inspiratory pressure (PImax), 120+/-6 cmH(2)O ) under different breathing conditions, The ipsilateral biceps brachii was chosen as the control muscle, The EMG was recorded from surface e lectrodes, but needle electrodes were also used for LD evaluation in a subset of three subjects, The EMG signal from both muscles was record ed simultaneously, rectified and integrated, with subtraction of the e lectrocardiographic signal Situations evaluated were: 1) maximal volun tary contraction (MVC); 2) apnoea; and 3) breathing under progressive inspiratory threshold loads (20-100% PImax, at 20% intervals), A close relationship was evident between LD recordings from surface and needl e electrodes (r=0.975), Activity of LD at baseline was 1.8+/-0.4% MVC, and showed a phasic increase during inspiration under loads, This cha nge had a linear tendency and was significant for loads corresponding to 40, 60, 80 and 100% of PImax when compared to the control muscle, A t this latter level, LD activity was equivalent to 32+/-5% MVC (range 11-61%), whereas mean activity of the control muscle was less than 7.5 % MVC. These results demonstrate that LD is progressively recruited in healthy subjects during inspiratory loading, and suggest that LD coul d participate as an accessory muscle for the breathing effort under sp ecific conditions, For these reasons, LD does not appear to be an appr opriate control for studies of the respiratory muscles.