Does Power Output at Critical Power Intensity Interchange between Cycling and Running?

e differences in power meters and gestures between cycling and running can have an impact on determining Critical Power (CP) intensity in each sport. CP is a concept that has been extensively researched in cycling, but with the advent of power measurement in running, it can now be examined in that discipline as well. The purpose of the present study was to determine whether power output at CP intensity is interchangeable between cycling and running segments measured with their respective discipline-speci c power meters. A group of 18 trained triathletes (age33.0 11.1 years , height 1.75 0.06 m, body mass 71.2 7.1 kg) performed a CP test in cycling (3-min All-Out Test) and running (9/3-min Stryd CP Test). The main results of the present study showed signi cant differences (p< 0.001) between CP in cycling and running. The running CP (301.8 W 41.5 W ) was 20.2% overestimated compared with the cycling CP (251.1 W 37.0 W). Cycling power only explained 26.7% of the running power (R 2 = 0.267;p= 0.284). Therefore, power would not be interchangeable between the cycling and running disciplines at CP intensity. In conclusion, it would be necessary to carry out a speci c test for each discipline to be able to make a correct determination of CP. Keywords: sensors; Stryd; watts; exercise testing;

power only explained 26.7% of the running power (R 2 = 0.267;p= 0.284). Therefore, power would not be interchangeable between the cycling and running disciplines at CP intensity. In conclusion, it would be necessary to carry out a speci c test for each discipline to be able to make a correct determination of CP. Keywords: sensors; Stryd; watts; exercise testing; endurance performance; eld; triathletes; measure 1. Introduction Endurance competitions, which combine two or more sports or disciplines, such as triathlon, are a relatively recent phenomenon that thousands of people participate in, and they are governed by rules and regulations [1]. In particular, the transfer of training effects between the swimming, cycling, and running disciplines has been studied in depth [2], making triathlon a complex sport. Rapid development in recent years has prompted industries to develop novel paradigms that allow coaches to accurately quantify the internal and external loads performed by athletes and help protect them from injury [3]. In brief, drafting is permitted in the swimming segment of the competition, as it is crucial for conserving energy in the following segments [4]. The term drafting is used to describe the tactic of performing a mode of activity in a protected position. In swimming, it has been shown that the metabolic cost of exercise is reduced by 5–10% during swimming in a drafting position, or the maximum speed is increased by 3.2–6% due to a reduction in frontal resistance or drag of 10–26% [5,6]. Considering that triathlon regulations allow any swimming technique to be used to cover the distance of the segment if the feet are not placed on the ground, the crawl technique is the most commonly used, as it is the fastest and most economical. The second and third segments of the triathlon require special attention [7]. Several authors consider the running segment to be the most decisive in achieving victory, given the greater variability of the time of this segment compared to the other two [8,9]. The cycling segment should also be analyzed because power output is the main measure of external load to measure intensity in this

segments of the triathlon require special attention [7]. Several authors consider the running segment to be the most decisive in achieving victory, given the greater variability of the time of this segment compared to the other two [8,9]. The cycling segment should also be analyzed because power output is the main measure of external load to measure intensity in this discipline [10], as well as being studied and compared in Appl. Sci.2023,13, 5511.

Appl. Sci.2023,13, 5511 2 of 9 this investigation with the running segment. This is essential to correctly understand the concept of power in the running segment. It is also important to note that performance in the cycling segment shows the best concordance with overall performance for both elite men and elite women at both sprint distances [11], as performance in the cycling segment shows the best concordance with overall performance as well as at Olympic distances [12]. In cycling, the increasing availability of power meters has led some authors [13] to associate a certain watt value to Functional Threshold Power (FTP) and other concepts such as Critical Power (CP). Currently, with the capability to calculate running power, these concepts have expanded within the sport. Allen and Coggan [13] de ned FTP as the highest power that can be maintained for 1 h. The Running Functional Threshold Power (rFTPw), measured in watts (W), is a measure of power associated with a certain intensity that can be calculated theoretically through a complex calculation model [14]. When using off-the-shelf power meters such as the Stryd Summit Power Meter (Boulder, CO, USA), data can be uploaded from various tests [15] to calculate the rFTPw or CP in the “Power Center” (https://www.stryd.com/powercenter, accessed 10 February 2023), which can be used to predict race times for different distances. However, a study of comparison between different tests to determine rFTPw concluded that it varies depending on the test performed and its duration [16]. The literature has explored the concept of CP from both a physiological and a math- ematical point of view. Mathematically, CP is de ned as the power asymptote of the hyperbolic relationship between power output and time to exhaustion [17]. For longer endurance events, it has been suggested that CP is most relevant to continuous activities lasting around 2 to 30 min [17]. This concept has also been applied to other sports, such as running [18], where the treadmill velocity–endurance time relationship for runs of 2 to 12 min duration conform to a similar hyperbolic function as that described for cycle ergometry [19]. From

it has been suggested that CP is most relevant to continuous activities lasting around 2 to 30 min [17]. This concept has also been applied to other sports, such as running [18], where the treadmill velocity–endurance time relationship for runs of 2 to 12 min duration conform to a similar hyperbolic function as that described for cycle ergometry [19]. From a physiological standpoint, CP represents the boundary between the steady state and a nonsteady state. As a result, it may offer a more signi cant performance indicator compared to other established benchmarks of aerobic tness, such as maximal O2uptake and the lactate threshold [17]. The CP concept has been used to distinguish the boundary between the heavy and severe exercise domains, which can be sustained for a duration of 15–40 min before exhaustion sets in or before the power output needs to be lowered to continue exercising [18]. Regardless of the approach taken, the ability to analyze mechanical power during running introduces a new paradigm in the scienti c literature of this eld. Currently, researchers have determined CP intensity in relation to ventilatory thresholds and maximum oxygen uptake [20]. The main purpose of this study was to investigate whether power output at CP in- tensity could be used interchangeably between cycling and running segments that were measured using their respective discipline-speci c power meters and trained triathletes. The previous hypothesis established was that the power output between cycling and run- ning would not be interchangeable at CP intensity because both the sport-speci c gestures (pedaling and stride) and the power meters are different between the two disciplines. 2. Materials and Methods 2.1. Participants A group of 18 trained triathletes participated in this study, all of whom were members of a local triathlon club. All triathletes ful lled the following criteria to be selected as trained triathletes [21]: (1) local-level representation, (2) regularly training more than 3 times per week, (3) identifying with the sport of triathlon speci cally, and (4) training with a purpose to compete. All participants read and signed an informed consent document in which they were informed

local triathlon club. All triathletes ful lled the following criteria to be selected as trained triathletes [21]: (1) local-level representation, (2) regularly training more than 3 times per week, (3) identifying with the sport of triathlon speci cally, and (4) training with a purpose to compete. All participants read and signed an informed consent document in which they were informed of the characteristics of this study and the strictly scienti c use of the data obtained, as speci ed in the Declaration of Helsinki of the World Medical Association (WMA); Ethical Principles for Medical Research Involving Human Subjects of 1975 (revised in Fortaleza, Brazil in 2013). This study has also been approved by the ethics committee of

Appl. Sci.2023,13, 5511 3 of 9 the University of Alicante (UA-2023-02-04). Descriptive data for the participants are shown in Table. Table 1.Anthropometric characteristics of the triathletes. Mean SD. Mean (M) Standard Deviation (SD) Age (years) 33.0 11.1 Body Mass (kg) 71.2 7.1 Body Height (m) 1.75 0.06 å8 skinfolds (mm) 71.9 22.9 Muscle Mass (kg) [22] 32.2 2.8 Fat Mass (kg) [23] 7.56 3.16 Fat Mass (%) [23] 10.5 3.4 2.2. Procedure An observational study design was employed to assess the possibility of exchanging power output at CP intensity between the cycling and running disciplines. This study was conducted in three test sessions. The initial session involved the anthropometric characteristics of the participants. In the second test session, the 9/3-minute Stryd CP test was performed. Following a rest period of at least 24 h, the 3-min All-Out test was carried out. Both the running and cycling tests were performed outdoors, in an identical weather environment and under the same weather conditions. The experimental procedure can be seen in Figure. Figure 1.Experimental procedure. 2.3. Anthropometry The body compositions of the triathletes were estimated using an anthropometric method, with all measurements taken by the same anthropometrist, who had achieved Level 1 of the International Society for the Advancement of Kinanthropometry (ISAK). The measurements were taken three times for each participant, following the Ross and Marfell-Jones [24] protocol. A Holtain skinfold caliper (Holtain Ltd., Crymych, UK), a Holtain bone-breadth caliper (Holtain Ltd., Crymych, UK), scales, a stadiometer, and anthropometric tape (SECA Ltd., Hamburg, Germany) were used as equipment. The physical characteristics of age, body mass, and height were measured in the following order: the biepycondilar-humerus, bistyloid, and biepicondylar-femur breadths; the relaxed-, exed-, and tensed-arm, waist, hip, and calf girths; and the tricep, subscapular, bicep, iliac-crest, supraspinal, abdominal, thigh, and calf skinfolds. Muscle mass was estimated using the Lee equation [22] and fat mass using the Withers equation [23]. 2.4. Running: Stryd CP Test To determine CP in running, the 9/3-min Stryd CP test proposed by the Stryd group was performed following protocol applied in previous investigations [20]. In this case, the test was

bicep, iliac-crest, supraspinal, abdominal, thigh, and calf skinfolds. Muscle mass was estimated using the Lee equation [22] and fat mass using the Withers equation [23]. 2.4. Running: Stryd CP Test To determine CP in running, the 9/3-min Stryd CP test proposed by the Stryd group was performed following protocol applied in previous investigations [20]. In this case, the test was conducted in the eld instead of with a treadmill in the laboratory. The test was carried out on an approved 400 m athletics track. All tests were conducted under normal weather conditions of temperature, wind, and no rain. For the warm-up, the triathletes performed for 10 min at low moderate intensity and then 2 to 3 high-intensity 1-min short bouts with 2 min of active rest. Following that, the running-power meter (Stryd Summit Power Meter) was fastened onto the laces of the right shoe. The main part of the exercise involved two maximum efforts of 9 and 3 min, respectively, with a 30-min active recovery

Appl. Sci.2023,13, 5511 4 of 9 break between the two efforts [20]. A researcher marked the starts and ends of the two maximum efforts by blowing a Fox 40 Classic whistle (Fox 40 International, Hamilton, Ontario, Canada) [25]. Athletes had immediate feedback on their wristwatch, of both the running pace (min/km) and the time remaining for each of the maximal efforts. The power output in absolute values (W) and relative to body mass (W/kg) in the 9- and 3-minute trials was entered into the Stryd CP calculator (https://www.stryd.com/ powercenter, accessed 10 February 2023). 2.5. Cycling: 3-min All-Out Test To determine CP in cycling, the 3-min All-Out test was performed following the proto- col applied in previous investigations [26,27]. The cycling test was conducted outdoors, with identical weather conditions to the running test. All participants used their own bicycles. The rear wheel of each bicycle was removed and attached to a direct drive Tacx Flow Ergotrainer (Technische Industrie Tacx BV, Oegstgeest, Netherlands) with 11 speeds (11–28 tooth). Triathletes rst performed a warm-up at 100 W, followed by 5 min of rest. The test started with 3 min of unloaded baseline pedaling at each subject's preferred cadence, followed by an all-out 3-min effort. Subjects were asked to increase their cadence to approx- imately 110 rpm during the last 5 s of the baseline period. Strong verbal encouragement was provided throughout the test, although the subjects were not informed of the elapsed time, to prevent pacing. To ensure all-out effort, subjects were instructed to maintain their cadence to be as high as possible at all times throughout the test. CP was calculated as the average power output during the nal 30 s [26,27]. For the cycling test to be valid, the maximum peak power had to be re ected within the rst 5 s of the start of the test. This was checked using the publicly available software Golden Cheetah (v 3.5, Cycling Power Analysis Software) and Microsoft Excel 2022 (Redmond, WA, USA). 2.6. Statistical Analysis All data are presented as mean SD. The Shapiro–Wilk test was used to study the normality of

power had to be re ected within the rst 5 s of the start of the test. This was checked using the publicly available software Golden Cheetah (v 3.5, Cycling Power Analysis Software) and Microsoft Excel 2022 (Redmond, WA, USA). 2.6. Statistical Analysis All data are presented as mean SD. The Shapiro–Wilk test was used to study the normality of the data. Student'st-test for independent samples was applied to determine the possible signi cant differences between the power outputs of the cycling and running tests both in absolute values and relative to body mass. Signi cance was established atp< 0.05. Levene's test for homogeneity of variance indicated that there was an equal distribution of variance. The magnitudes of differences and effect sizes (ESs) were calculated according to Cohen'sd[28] and interpreted as trivial, (ES < 0.2), small (0.2 ES < 0.4), moderate (0.4 ES < 0.8), or large (ES 0.8). The linear regression model and the coef cient of determination (R 2 ) [29] were used to determine the degree to which cycling power output explained variations in running power output. All data were analyzed using the SPSS 28.0 statistical package (SPSS Inc., Chicago, IL, USA). 3. Results Table (W/kg) of the triathletes during the 9/3 Stryd CP test of running. The absolute and relative power values were higher in the 3-min effort than in the 9-min effort, these efforts being performed at 110.11 13.36% CP and 104.01% CP, respectively. The determination of CP in the triathletes was carried out at 301.8 41.5 W and 4.23 0.51 W/kg. Table 2.Critical Power in running, determined with the 9/3 Stryd Test. Mean SD. 9-Min Effort 3-Min Effort Distance (km) 2.52 0.21 0.93 0.08 Absolute Power (W) 313.9 35.5 332.3 40.3 Relative Power (W/kg) 4.40 0.40 4.66 0.52 % Critical Power 104.01 11.75 110.11 13.36 Critical Power (W) 301.8 41.5 Critical Power (W/kg) 4.23 0.51

Appl. Sci.2023,13, 5511 5 of 9 The absolute (W) and relative to body mass (W/kg) power values of the triathletes during the 9/3 Stryd CP test in running are shown in Figure. In the 3-min effort, the triathletes achieved the highest absolute (332.3 40.3) and relative power (4.66 0.52) records. In the 9-min effort, the absolute (313.9 35.5) and relative power (4.40 0.40) records were lower. The CP values obtained from the Stryd CP calculator were lower than both the 3-min and 9-min values. Figure 2. Power records during the 9/3 Stryd CP test. Columns shown in black for absolute power and gray for power relative to body mass. Figure disciplines. There are signi cant differences and large ESs between the cycling and running CP in both absolute watts (W) (p< 0.001; ES = 1.29) and watts relative to body mass (W/kg) (p< 0.001; ES = 1.25). The running CP (301.8 W 41.5 W) was 20.2% overestimated compared with the cycling CP (251.1 W 37.0 W). Linear regression analysis showed that cycling power output explains only 26.7% of the running power output (R 2 = 0.267; p= 0.284). Figure 3. Critical Power records between the cycling and running disciplines. Columns shown in black for absolute power and gray for power relative to body mass. *p< 0.001. 4. Discussion The main purpose of the present study was to determine whether power output at CP intensity could be interchangeable between cycling and running segments. Although both the power meters and the sport-speci c gestures in each of these disciplines are different,

Appl. Sci.2023,13, 5511 6 of 9 triathletes could be ideal participants for this type of study due to their previous familiarity with both technical gestures, pedaling and stride, respectively. To the best of our knowledge, this study provides the rst comparison of CP values between cycling and running. While a theoretical basis for power application exists in cycling [10,13,30–34], a more detailed examination of running power is necessary. Firstly, it is important to note that the available information on running power is limited [35]. However, the concept of power in running has been systematically re- viewed [36,37]. The validity and reliability of one of the main devices for measuring power output [38], the Stryd running-power meter (Stryd Summit Power Meter, Boulder, CO, USA) has been studied at different running speeds [39], as well as in other modalities such as walking [40] and trail walking [41]. Additionally, data training metrics have been analyzed with this device [42–44]. The CP concept has been investigated from a physi- ological perspective, including its relationship to ventilatory thresholds and maximum oxygen uptake [20] as well as its association with physiological variables such as oxygen consumption [45] and changes in power as functions of different intervals [46]. One of the main advantages of the Stryd running-power meter is its practical applications for data collection in both training and competition settings, in contrast to laboratory-based devices [47]. Secondly, in relation to running power, it is worth highlighting a study by Ruiz- Alias et al. [20], in which CP was determined with respect to ventilatory thresholds and maximum oxygen uptake using the same 9/3-minute Stryd CP test proposed by the Stryd group. In that study, conducted on 15 high-caliber athletes, higher values of CP were observed (4.67 0.42 W/kg ) compared with those found in our trained triathletes (4.23 0.51 W/kg ). Similarly, higher values were observed for the 15 high-caliber athletes in the two efforts performed in the running test to determine the CP, in the maximum efforts of both 9 min (4.91 0.42 W/kg vs. 4.40 0.40 W/kg) and 3 min (5.39 0.44 W/kg vs. 4.66

This study investigates the interchangeability of power output at critical power intensity between cycling and running.