title: Heart rate deflection point as a strategy to defend stroke volume during incremental exercise.
abstract: 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 O(2) uptake (Vo(2 max)) in the HRDP group, whereas it increased until 94.4 +/- 8.6% of the power associated with Vo(2 max) in six other subjects (no-HRDP group, P = 0.004). Neither SV(max) (ml/beat or ml.beat(-1).m(-2)) nor Vo(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.
authors.affiliation: LEPHE, Department of STAPS, University of Evry Val d'Essonne, Sport Medicine Center of the CCAS, 2 Ave. Richerand, Paris F-75010, France. lepretre.pierre-marie@wanadoo.fr
authors.forename: Pierre-Marie
authors.initials: PM
authors.lastname: Lepretre
authors.forename: Carl
authors.initials: C
authors.lastname: Foster
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Koralsztein
authors.forename: Veronique L
authors.initials: VL
authors.lastname: Billat
mesh_terms: D000328:Adult; D001784:Blood Gas Analysis / Q000379:methods; D005080:Exercise Test / Q000379:methods; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D005082:Physical Exertion / Q000502:physiology*; D013318:Stroke Volume / Q000502:physiology*; D013997:Time Factors