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

Abstract

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 O(2) uptake ([Formula: see text]), 2 min] was repeated three times (IE(1st), IE(2nd) and IE(3rd)) 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 [Formula: see text]), and a further resting recovery for 40-60 min. Blood pH during IE and subsequent 20-min recovery was significantly higher in the IE(3rd) than in the IE(1st) (P < 0.05). Effort sense of legs during IE was significantly higher in the IE(3rd) than in the IE(1st) and IE(2nd). Integrated EMG (IEMG) measured in the vastus lateralis during IE was significantly lower in the IE(3rd) than in the IE(1st). In contrast, mean power frequency of the EMG was significantly higher in the IE(2nd) and the IE(3rd) than in the IE(1st). Ventilation ([Formula: see text]) in the IE(3rd) was significantly higher than that in the IE(1st) 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.

The effect of glycogen reduction on cardiorespiratory and metabolic responses during downhill running

“…Decreased RER and decreased blood glucose concentration during the RED downhill run is indicative of greater fat oxidation. For a given concentric workload, increased fat metabolism in type I fibres elevates O , to a greater degree than carbohydrate metabolism (Vøllestad et al 1984; Yamanaka et al 2012 Whether this is true for eccentric exercise remains to be seen, yet lower RER provides an indirect measure of our glycogen reduction protocol, as fat oxidation rate is determined by carbohydrate availability (Holloszy et al 1998 ).…”

Relationship between motor corticospinal excitability and ventilatory response during intense exercise

“…This hyperventilatory response is considered to be respiratory compensation to minimize a decrease in blood pH (Kowalchuk et al 1988;Rausch et al 1991;Ward 2007;Wasserman et al 1986;Yunoki et al 1999), and the decrease in blood pH per se has been regarded as an important factor enhancing ventilation during exercise above the lactate threshold (Stringer et al 1992;Wasserman et al 1975). However, by using a glycogen-reduction procedure (Gollnick et al 1974;Heigenhauser et al 1983; Sabapathy et al 2006), which can manipulate the degree of metabolic acidosis, we found that hyperventilatory response to IE is not dependent on blood pH but is associated with effort sense of exercising muscle (Yamanaka et al 2011;Yamanaka et al 2012). …”

“…In this kind of situation, there is a possibility that activation of upstream regions of the motor cortex might be involved in the generation of a greater effort sense and consequently an increase in ventilation in order to maintain a required power output during IE (Amann et al 2013). Therefore, in the present study, using the glycogen-reduction procedure adopted in our previous study (Yamanaka et al 2012), we examined the relationship between effort-mediated ventilatory response and corticospinal excitability of lower limb muscle during IE. It has been shown that moderate-intensity exercise decreased muscle glycogen content to half of the pre-exercise level in about 45 min (Gollnick et al 1974).…”

“…However, it has been confirmed that during IE performed after muscle glycogen reduction, integrated electromyogram (iEMG) activity recorded in exercising muscle, which reflects central motor command (Amann et al 2006;Amann and Dempsey 2008), does not increase while ventilation is elevated (Osborne and Schneider 2006;Perrey et al 2003;Yamanaka et al 2012). These findings indicate the possibility that although ventilatory response to IE is related to effort sense, an increase in motor drive from the motor cortex to exercising muscles, which may produce effort sense via efference copy/corollary discharge mechanisms (Marcora 2009;Sperry 1950;Von Holst 1954), is not always required for the augmented ventilatory response to IE (Yamanaka et al 5 5 2012;Yunoki 2012).…”

“…Pedaling frequency during the two IEs and a submaximal exercise was averaged over a 30-s interval. A further resting recovery was provided for 60 min before the start of the second IE trial (IE 2nd ) in order to restore the disturbance of physiological parameters (i.e., blood acid-base parameters, muscle temperature, and cardiopulmonary parameters) (Yamanaka et al 2012). The subjects were permitted to drink only water ad libitum during the 45-min submaximal exercise and subsequent 60-min resting recovery.…”