Identifying the integrated electromyographic threshold using different muscles during incremental cycling exercise.

BACKGROUND The purpose of this study was to identify the IEMG threshold in the vastus lateralis (VL) and rectus femoris (RF) muscles during progressive, incremental exercise and to relate these thresholds to the ventilatory threshold (Tvent). METHODS Ten men (age: 23.40 +/- 3.13 yrs, mass 76.64 +/- 8.13 kg, % fat: 8.81 +/- 2.32, VO2peak: 66.37 +/- 10.61 ml.kg.min-1) with cycling experience completed a graded exercise test on a cycle ergometer by cycling at 90 rpm using 45 watt increments at two minute intervals. Oxygen uptake was measured continuously and the IEMG activity of the VL and RF was calculated during the last 5 s of each minute. The mean for the IEMG of 6 to 7 complete pedal revolutions was used as the final value. Tvent was visually identified using the VE/VO2 and V-slope methods. The IEMG threshold for VL and RF was visually identified at the inflection point where a non-linear increase in IEMG occurred. Comparisons between Tvent and IEMG thresholds were made using dependent means "t"-tests. RESULTS Results showed that an IEMG threshold was identified in all 10 subjects for the RF, but in only 5 of 10 subjects for the VL. However, when identified, the IEMG threshold for VL was similar to RF.VO2 at IEMG threshold for RF (3.53 +/- 0.36 L.min-1) was not significantly different from Tvent (3.36 +/- 0.42 L.min-1). CONCLUSIONS These results show that the IEMG threshold is more consistently detected in the RF compared to VL during incremental cycling exercise. In addition, the IEMG threshold for RF was closely related to Tvent and provides an alternative means to assess the ventilatory threshold.