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Heart rate deflection point as a strategy to defend stroke volume during incremental exercise

¹Laboratoire d'Etude de la Physiologie de l'Exercice, Department of Sciences and Technology in Sports and Physical Activities, University of Evry Val d'Essonne, Evry, France ²University of Wisconsin-La Crosse, La Crosse, Wisconsin; and ³Sport Medicine Center of the Caisse Centrale d'Activités Sociales, Paris, France

Submitted 4 August 2004 ; accepted in final form 29 November 2004

The purpose of this study was to examine whether the heart rate (HR) deflection point (HRDP) in the HR-power relationship is concomitant with the maximal stroke volume (SV_max) value achievement in endurance-trained subjects. Twenty-two international male cyclists (30.3 ± 7.3 yr, 179.7 ± 7.2 cm, 71.3 ± 5.5 kg) undertook a graded cycling exercise (50 W every 3 min) in the upright position. Thoracic impedance was used to measure continuously the HR and stroke volume (SV) values. The HRDP was estimated by the third-order curvilinear regression method. As a result, 72.7% of the subjects (HRDP group, n = 16) presented a break point in their HR-work rate curve at 89.9 ± 2.8% of their maximal HR value. The SV value increased until 78.0 ± 9.3% of the power associated with maximal O₂ uptake (O_{2 max}) in the HRDP group, whereas it increased until 94.4 ± 8.6% of the power associated with O_{2 max} in six other subjects (no-HRDP group, P = 0.004). Neither SV_max (ml/beat or ml·beat^–1·m^–2) nor O_{2 max} (ml/min or ml·kg^–1·min^–1) were different between both groups. However, SV significantly decreased before exhaustion in the HRDP group (153 ± 44 vs. 144 ± 40 ml/beat, P = 0.005). In the HRDP group, 62% of the variance in the power associated with the SV_max could also be predicted by the power output at which HRDP appeared. In conclusion, in well-trained subjects, the power associated with the SV_max-HRDP relationship supposed that the HR deflection coincided with the optimal cardiac work for which SV_max was attained.

physical work curve break point; left ventricular ejection fraction; cycling graded test

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