COMPARISON OF LACTATE AND ELECTROMYOGRAPHICAL THRESHOLDS AFTER AN EXERCISE BOUT RONALD L. SNARR, 1 MICHAEL R. ESCO, 2 DANILO V. TOLUSSO, 2 ASHLEIGH V. HALLMARK, 2 RYAN L. EARLEY, 3 JOHN C. HIGGINBOTHAM, 4 MICHAEL V. FEDEWA, 2 AND PHILIP BISHOP 2 1 Department of Health Sciences & Kinesiology, School of Health and Kinesiology, Georgia Southern University, Statesboro, Georgia; Departments of 2 Kinesiology; 3 Biological Sciences; and 4 Community Medicine and Population Health, The University of Alabama, Tuscaloosa, Alabama ABSTRACT Snarr, RL, Esco, MR, Tolusso, DV, Hallmark, AV, Earley, RL, Higginbotham, JC, Fedewa, MV, and Bishop, P. Comparison of lactate and electromyographical thresholds after an exercise bout. J Strength Cond Res 33(12): 3322–3331, 2019—The electromyographical threshold (EMG T ) has been previously val- idated as a means to predict the work rate at which lactate threshold (LT) occurs. The reliability of these measures has yet to be examined after a bout of exercise. The purpose was to determine the agreement between electromyography (EMG) and LT after a 30-minute bout of steady-state aerobic exercise. Participants completed 2 graded exercise tests (GXT) on a cycle ergometer separated by 30 minutes of steady-state exercise. Blood lactate was measured the last 45 seconds of each stage during both GXTs, whereas EMG of the vastus lateralis was monitored continuously. Individual agreement demonstrated that pre-exercise and post-exercise LT occurred at the same work rate in 2 of 10 participants, whereas EMG T occurred at the same work rate in 6 of 10 participants. Results showed no mean difference between work rates for LT or EMG threshold for the pre-exercise GXT, but LT was significantly lower (p , 0.01) than EMG T during the post-exercise GXT. Post-GXT LT work rates were also determined to be signifi- cantly lower than pre-GXT LT (p = 0.034), whereas no differ- ences existed in EMG thresholds. Although both LT and EMG T testing may display similar properties, they are not interchange- able. The physiological responses to increasing exercise inten- sity between La and EMG signaling seem to be associated, and their interaction may not be cause-effect. Because of poor individual agreement, caution should be used when determin- ing LT through the use of EMG. Further research is needed to determine the ability of these 2 metrics to prescribe training intensities. KEY WORDS lactate threshold, training, electromyography, cycling, aerobic training INTRODUCTION L actate threshold (LT) training is a form of cardio- vascular endurance training that consists of per- forming sustained aerobic activity at the speed, power output, or percentage of V _ O 2 max at which blood lactate concentration ([La]) begins a rapid increase above baseline (25,31). Training at an intensity equal to or above the LTcan result in favorable performance adaptations such as improved aerobic power and lactate clearance (25,10,14). In addition, steady-state training below LT for an extended period can be especially important for periph- eral adaptations such as increased capillary and mitochon- drial densities (26). Although most investigations focus on the importance of threshold-based programming in trained and elite endurance competitors, LT testing may also have important implications for baseline measures, monitoring progress, as well as exercise prescription, among untrained participants. Previous investigations using surface electromyography (EMG) have demonstrated increases in motor unit recruit- ment patterns with an increase in work rate, particularly during graded exercise testing (GXT) (16,21,29). This increase in motor unit recruitment at an exponential rate has been identified as the electromyographical threshold (EMG T ) (20). Because this increase in EMG amplitude also occurs near the LT, the EMG T has been suggested as a non- invasive surrogate to blood lactate testing (7,12). Traditional LTand EMG T testing begins with an individ- ual in a rested state (i.e., La value under 1.0 mmol$L 21 ) and shows small increases in [La] and EMG amplitude over time until a threshold point is reached. Lactate threshold and EMG T values indicate work rates (i.e., Watts, percentage Address correspondence to Dr. Ronald L. Snarr, rsnarr@ georgiasouthern.edu. 33(12)/3322–3331 Journal of Strength and Conditioning Research Ó 2019 National Strength and Conditioning Association 3322 Journal of Strength and Conditioning Research the TM Copyright © 2019 National Strength and Conditioning Association. Unauthorized reproduction of this article is prohibited.