100 www.IJSPP-Journal.com ORIGINAL INVESTIGATION International Journal of Sports Physiology and Performance, 2014, 9, 100 -107 http://dx.doi.org/10.1123/IJSPP.2013-0298 © 2014 Human Kinetics, Inc. From Heart-Rate Data to Training Quantification: A Comparison of 3 Methods of Training-Intensity Analysis Øystein Sylta, Espen Tønnessen, and Stephen Seiler Purpose: The authors directly compared 3 frequently used methods of heart-rate-based training-intensity- distribution (TID) quantiication in a large sample of training sessions performed by elite endurance athletes. Methods: Twenty-nine elite cross-country skiers (16 male, 13 female; 25 ± 4 y; 70 ± 11 kg; 76 ± 7 mL · min –1 · kg –1 VO 2max ) conducted 570 training sessions during a ~14-d altitude-training camp. Three analysis methods were used: time in zone (TIZ), session goal (SG), and a hybrid session-goal/time-in-zone (SG/TIZ) approach. The proportion of training in zone 1, zone 2, and zone 3 was quantiied using total training time or frequency of sessions, and simple conversion factors across different methods were calculated. Results: Comparing the TIZ and SG/TIZ methods, 96.1% and 95.5%, respectively, of total training time was spent in zone 1 (P < .001), with 2.9%/3.6% and 1.1%/0.8% in zones 2/3 (P < .001). Using SG, this corresponded to 86.6% zone 1 and 11.1%/2.4% zone 2/3 sessions. Estimated conversion factors from TIZ or SG/TIZ to SG and vice versa were 0.9/1.1, respectively, in the low-intensity training range (zone 1) and 3.0/0.33 in the high-intensity train- ing range (zones 2 and 3). Conclusions: This study provides a direct comparison and practical conversion factors across studies employing different methods of TID quantiication associated with the most common heart-rate-based analysis methods. Keywords: XC skiers, endurance training, intensity distribution, time in zone, session goal Sylta and Seiler are with the Faculty of Health and Sport Sci- ences, University of Agder, Kristiansand, Norway. Tønnessen is with the Norwegian Olympic Federation, Oslo, Norway. The training dose-adaptive response relationship is at the core of sports physiology and performance. However, quantifying training dose remains an area of some confusion. Focusing on endurance athletes, training dose can be measured in terms of external work executed (distance, power, velocity) 1,2 or internal physiological responses elicited by that work (heart rate [HR], blood lactate, VO 2 ). 3–13 Training dose can also be measured by how the stimulus was perceived (session rating of per- ceived exertion [RPE]). 12,14–18 Most high-level endurance athletes maintain a training diary where they report their training. In reality, some combination of all 3 of these basic descriptions of the training dose is usually relected in athlete self-report. 1–3,6–8,10–12,19,20 Three basic approaches are described in the lit- erature for quantifying endurance-training sessions based on the HR response. One approach is time in zone (TIZ). 4,5,9–12 Dedicated software allocates HR registration data to intensity zones deined from cutoffs registered in the software by the athlete or coach. A second method is session goal (SG). 12 This categorical approach assigns the entire session into a single inten- sity zone with the assumption that the “goal portion” of the session primarily determines its impact as an adaptive signal and source of physiological stress. A categorical approach likely gives a realistic picture of the total training-intensity distribution (TID) over the long term and is frequently cited in the literature. 12,14–18 The SG method has also been found to agree well with intensity categorization based on session RPE (sRPE). 12 A third approach is a hybrid combination of SG and TIZ, called the modiied SG approach (SG/TIZ) in the literature. 6–8,13,19 The goal of the session is used to aid in allocating training time to intensity zones, based on a combination of actual HR registration and workloads applied. Figure 1 illustrates the 3 methods by depicting beat-for-beat HR responses to a typical endurance ses- sion lasting ~90 minutes. The elite athlete performed interval training organized as 5 × 8-minute work periods with 2-minute recoveries, in addition to a warm-up and cooldown period. Blood lactate concentrations during the irst, third, and fourth rest periods were 3.5, 4.2, and 5.6 mmol/L, respectively. The session was prescribed as a zone 3 interval session based on the 3-zone model (Table 1). The athlete’s maximal HR is 200. The TIZ method uses the HR curve (solid line) to allocate time in different zones. Thirty-ive minutes are distributed in zone 3, plus 48 minutes in zone 1 and 5 minutes in zone 2. The SG approach categorizes this whole workout as a zone 3 session based on the highest intensity achieved