Abbey C. Hafler, Daniela Rincon Garcia, Erica M. Marshall. Florida Southern College, Lakeland, FL.

BACKGROUND: High-load resistance exercise (HL-RE) prolongs the QT interval, which is associated with increased risk of ventricular arrhythmias. However, the effects of low-load blood flow restriction exercise (LL-BFRE) on the QT interval are unclear. Therefore, the purpose of this study was to compare changes in the QT interval following HL-RE and LL-BFRE. METHODS: Nine individuals (Mean±Standard Deviation (SD): Age: 21±3 years; Men: 7; Women: 2) volunteered to participate. Heart rate (HR) signals from the electrocardiogram (ECG) were used to derive the HR and QT interval using PowerLab data acquisition system and LabChart Pro software (ADInstruments, Sydney, Australia). HR signals were collected at rest, immediately post-exercise (IP), 10-, 30- and 45-minutes post-exercise. HL-RE consisted of 4 sets of 8 repetitions at 70% of the one repetition maximum (1RM). LL-BFRE was performed with a knee wrap (LL-kBFRE) and pneumatic cuff (LL-pBFRE), which consisted of 4 sets of 30, 15, 15, and 15 repetitions at 30% of the 1RM. Prior to analysis, QT interval was rate corrected (QTc) according to Bazzett. Two-Way Repeated Measures ANOVAs were used to examine the effect of condition (HL-RE, LL-kBFRE, LL-pBFRE) across time (Rest, 10, 30 and 45 minutes) on HR and QTc interval. Significant effects were analyzed using pairwise comparisons with a Sidak correction factor. Statistical significance was set a priori at p≤0.05. RESULTS: There were significant condition by time interactions for HR (p=0.006, ηp2 =0.38) and QTc interval (p=0.015, ηp2 =0.38), as well as main effects of time for HR (p≤0.001, ηp2 =0.81) and QTc interval (p≤0.001, ηp2 =0.82). Across all conditions, HR was increased IP (74±12 bpm), and at 10 (68±11 bpm) and 30-minutes (63±8 bpm) compared to Rest (55±8 bpm). However, the HR response was greater following HL-RE (80±17 bpm) compared to LL-pBFRE (69±11 bpm) in the IP period. The QTc interval was also increased across all conditions IP (3970.1±187.5 msec) and at 10 minutes (3851.6±210.2 msec) compared to Rest (3667.6±274.8 msec), but prolongation was greater following HL-RE (4053.3±243.0 msec) compared to LL-pBFRE (3868.1±173.9 msec). CONCLUSIONS: This study suggests that HLRE and LL-BFRE transiently increase the HR and lengthen the QT interval. However, for at least 10 minutes, these changes are augmented following HLRE more so than LL-pBFRE.

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