Relationship between effort sense and ventilatory response to intense exercise performed with reduced muscle glycogen

The purpose of the present study was to examine the effects of muscle glycogen reduction on surface electromyogram (EMG) activity and effort sense and ventilatory responses to intense exercise (IE). Eight subjects performed an IE test in which IE [100–105% of peak O2 uptake (\( \dot{V}{\text{O}}_{{2{\text{peak}}}} \)), 2 min] was repeated three times (IE1st, IE2nd and IE3rd) at 100–120-min intervals. Each interval consisted of 20-min passive recovery, 40-min submaximal exercise at ventilatory threshold intensity (51.5 ± 2.7% of \( \dot{V}{\text{O}}_{{2{\text{peak}}}} \)), and a further resting recovery for 40–60 min. Blood pH during IE and subsequent 20-min recovery was significantly higher in the IE3rd than in the IE1st (P < 0.05). Effort sense of legs during IE was significantly higher in the IE3rd than in the IE1st and IE2nd. Integrated EMG (IEMG) measured in the vastus lateralis during IE was significantly lower in the IE3rd than in the IE1st. In contrast, mean power frequency of the EMG was significantly higher in the IE2nd and the IE3rd than in the IE1st. Ventilation (\( \dot{V}{\text{E}} \)) in the IE3rd was significantly higher than that in the IE1st during IE and the first 60 s after the end of IE. These results suggest that ventilatory response to IE is independent of metabolic acidosis and at least partly associated with effort sense elicited by recruitment of type II fibers.