Influence of Biomechanical Parameters on Performance in Elite Triathletes along 29 Weeks of Training

he purpose of the study was to assess how the modi cation of biomechanical parameters in uences the performance of elite triathletes. Four elite international triathletes participated in this study. The anthropometric method ISAK was used to estimate the triathlete's body composition. For the physiological and biomechanical parameters, a running test (RT) was performed on an outdoor track, with the participants wearing the Stryd Summit Footpod (Stryd, Boulder, CO, USA). The pre-test took place in the last week of an adaptation mesocycle; then, after 29 weeks of training, the triathletes performed the post-test. A within-subject repeated measures design was used to assess changes in the anthropometric, physiological and biomechanical parameters. Pearson correlations (r) were applied to determine the relationship between the performance at different intensities (VT1, VT2 and MAS) and the biomechanical parameters. Concerning the anthropometric characteristics, signi cant differences were found in the summation (S) of skinfold (8.1 cm); as a consequence, the % fat mass was reduced (1.2%). Signi cant differences were found in the physiological values (VO 2and % VO 2max), speed and biomechanical parameters, such as step length normalized, to the speci c physiological intensity of the short-distance triathlon, the VT2. Therefore, performance improvement in the running segment could not only be explained by

(8.1 cm); as a consequence, the % fat mass was reduced (1.2%). Signi cant differences were found in the physiological values (VO 2and % VO 2max), speed and biomechanical parameters, such as step length normalized, to the speci c physiological intensity of the short-distance triathlon, the VT2. Therefore, performance improvement in the running segment could not only be explained by physiological changes, but also by biomechanical parameters changes. Keywords:Stryd; eld; training; spatiotemporal parameters; physiology; anthropometry 1. Introduction Triathlon is an endurance sport that comprises a sequential swim, swim-to-cycle transition, cycle, cycle-to-run transition, and run over a variety of long or short distances [1]. Standard races are stipulated by the International Triathlon Union (ITU), including sprint distance (750 m swimming, 20 km cycling and 5 km running) and Olympic distance (1.5 km swimming, 40 km cycling and 10 km running). Although the in uence of the segments on the overcome result has been widely studied [2–6], the running segment has been the most studied. In the running segment was found the greatest variation in times for all male world championship triathletes [7]. Previous ndings also have shown that running performance is the primary determinant of success in high-level short-distance triathlon races [8]. Other authors concluded that strategies to improve time in the running segment should be the main focus in the preparation of the short-distance triathlon [4]. However, to date, the physiological [9] and biomechanical changes in the performance of the world's best elite triathletes in short-distance triathlons have not been widely investigated. Concerning the triathlon performance factors, some authors differentiate between an ergogenic analysis for the determination of the internal load and an analytical analysis for the determination of the technical and tactical physical conditioning factors [10]. Internal load values have been previously studied in elite triathletes [10]—for example, for prescribing the heart rate (HR) zones for training from cycling to running [11]—to determine their signi cant maximum oxygen uptake (VO2max) [12–14]. Nevertheless, Appl. Sci.2021,11, 1050.

have been previously studied in elite triathletes [10]—for example, for prescribing the heart rate (HR) zones for training from cycling to running [11]—to determine their signi cant maximum oxygen uptake (VO2max) [12–14]. Nevertheless, Appl. Sci.2021,11, 1050.

Appl. Sci.2021,11, 1050 2 of 12 performance in triathlon has been associated with the capability of the triathlete to exercise at a lower percentage of VO2max, which is in uenced by different factors such as aerobic power, economy of movement and ventilatory threshold 2 (VT2) [15]. The in uence of biomechanical factors on performance has also been widely studied. Moore [16] classi ed them as spatiotemporal, kinematics, kinetics and neuromuscular, although running speed is mainly de ned by spatiotemporal parameters, such as step frequency (SF) and step length (SL), which are mutually dependent. Although from a physiological and training point of view running performance has been widely studied, the possible in uence of spatiotemporal variables on performance is still an issue of discussion [17]. Even more in elite triathletes due to the lack of analytical analysis of the running segment [10], unlike trained and novice runners [17–19]. To understand the in uence of biomechanical parameters on performance, anthropometric characteristics must be considered because some of them in uence the running success in triathlon [20]. In the last few years, there is a tendency to produce low-cost, portable gait analysis equipment, which has a great advantage over previous methods of analysis that have generally required well-equipped research laboratories [21]. Higginson et al. [22] point out that, from a practical point of view, through accelerometry it is possible to measure the participants in a more natural environment instead of an arti cial laboratory. This is important for interpreting the data, taking into account the speci city of the sport because some biomechanical variables, such as leg stiffness, have been shown to in uence perfor- mance [23,24] while running in speci c situations rather than in non-speci c situations, such as vertical jumps [18,19]. Currently, Stryd (Stryd Summit Model, Boulder, CO, USA) is a practical portable device that is reliable for measuring running metrics, classi ed as adequate for running assessment [25]. The concurrent validity of Stryd as compared to OptoGait was low–moderate for contact time (CT) and ying time (FT) and excellent for step length (SL) and step frequency (SF) [25]. This

[18,19]. Currently, Stryd (Stryd Summit Model, Boulder, CO, USA) is a practical portable device that is reliable for measuring running metrics, classi ed as adequate for running assessment [25]. The concurrent validity of Stryd as compared to OptoGait was low–moderate for contact time (CT) and ying time (FT) and excellent for step length (SL) and step frequency (SF) [25]. This device also has been used in other investigations, showing signi cant correlations between run mechanics such as contact time, vertical oscillation (VO), step frequency and metabolic demand (VO2/speed) [26]. For this reason, a current systematic review concludes that this device could be a valid tool for measuring temporal parameters [27]. Thus, the main purpose of this study was to analyze the changes in biomechanical parameters in elite triathletes throughout an elite triathlon season. Anthropometric and physiological variables also were analyzed to jointly interpret changes in the running biomechanics. A previous hypothesis re ects that the physiological and anthropomet- ric values will improve and that the spatiotemporal parameters could have a different interpretation than for novice or untrained triathletes measured in a laboratory. 2. Materials and Methods 2.1. Sample Only 44 triathletes out of 100 participants nished the Spanish Olympic Elite Triathlon Championship in 2019; the remaining 66 participants were lapped or did not nish (DNF) the race. Elite international men triathletes (n = 4), who represent 9% of the elite Spanish triathletes, belonging to the same training group and team, participated in the study (age range: 19–24 years; age: 22.5 1.9 years; height: 1.84 4.1 m (mean SD)). All triathletes provided written informed consent to take part in this study, which was previously ap- proved by the Research Ethics Committee of the University of Alicante (UA-2019-05-13). A summary of the training history and racing during the 29 weeks for these subjects is presented in Figure.

Appl. Sci.2021,11, 1050 3 of 12Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 12 Figure 1. Historical objective load scale (ECOs) training load in the disciplines of swimming, cycling and running per- formed by the triathletes during the season. Besides, the triathletes also carried out a resistance programme throughout the sea- son, with different objectives in each mesocycle, according to the assessment of strength and power in resistance training of Naclerio [28,29]. In the first period of the season (gen- eral preparatory period), three weekly sessions were performed during two mesocycles (8 weeks) of endurance strength with low weights (2–4 sets of 8–16 repetitions at 30–40% of 1RM). In the second period of the season (specific preparatory period), two sessions per week were performed during two mesocycles (8 weeks) of explosive strength (2–4 sets of 6–8 repetitions at 50–60% of 1RM). Later, and also during the specific preparatory period, they performed two sessions per week during 1 strength mesocycle (4 weeks) at high ex- ecution speeds during the concentric phase (2–4 sets of 2–4 repetitions at 80% of 1RM), including plyometrics exercises. Finally, during the third period of the season (competi- tive period), they performed two sessions per week of another mesocycle (4 weeks) of explosive strength (2–4 sets of 6–8 repetitions at 50–60% of 1RM), except in competition weeks where no strength session was done. For the rest of the season (last five weeks), they only performed one day of explosive strength. Concerning the training session, two exercises were done in each workout, one for the upper body (pull-up or bench press) and another for the lower body (squat, deadlift or hip thrust). Mobility exercises were also included in the warm-up for the swimming and re- sistance sessions, and also for the running sessions (only when intense sessions were car- ried out at or above the second ventilatory threshold). 2.2. Procedures 2.2.1. Study Protocol Before starting the elite national triathlon season, the triathletes rested for two full weeks between the previous and current season. During the first month, all triathletes took part in a mesocycle of adaptation

sessions, and also for the running sessions (only when intense sessions were car- ried out at or above the second ventilatory threshold). 2.2. Procedures 2.2.1. Study Protocol Before starting the elite national triathlon season, the triathletes rested for two full weeks between the previous and current season. During the first month, all triathletes took part in a mesocycle of adaptation according to the principles of progression and su- per-compensation training (three weeks of training load and one week of recovery). Dur- ing this adaptation mesocycle, the triathletes performed four microcycles of 15%, 20%, 25% and 15% of the peak load microcycle of the season along the first, second, third and fourth week, respectively. The running pre-test took place in the last week of this adapta- tion mesocycle. After 29 weeks of training, the running post-test was performed. Three 0 100 200 300 400 500 600 700 800 Training Load (ECOs) Historical Training Load (ECOs) ECOs Swimming ECOS Cycling ECOs Running Figure 1. Historical objective load scale (ECOs) training load in the disciplines of swimming, cycling and running performed by the triathletes during the season. Besides, the triathletes also carried out a resistance programme throughout the season, with different objectives in each mesocycle, according to the assessment of strength and power in resistance training of Naclerio [28,29]. In the rst period of the season (gen- eral preparatory period), three weekly sessions were performed during two mesocycles (8 weeks) of endurance strength with low weights (2–4 sets of 8–16 repetitions at 30–40% of 1RM). In the second period of the season (speci c preparatory period), two sessions per week were performed during two mesocycles (8 weeks) of explosive strength (2–4 sets of 6–8 repetitions at 50–60% of 1RM). Later, and also during the speci c preparatory period, they performed two sessions per week during 1 strength mesocycle (4 weeks) at high execution speeds during the concentric phase (2–4 sets of 2–4 repetitions at 80% of 1RM), including plyometrics exercises. Finally, during the third period of the season (competitive period), they performed two sessions per week of another mesocycle (4 weeks) of explo-

the speci c preparatory period, they performed two sessions per week during 1 strength mesocycle (4 weeks) at high execution speeds during the concentric phase (2–4 sets of 2–4 repetitions at 80% of 1RM), including plyometrics exercises. Finally, during the third period of the season (competitive period), they performed two sessions per week of another mesocycle (4 weeks) of explo- sive strength (2–4 sets of 6–8 repetitions at 50–60% of 1RM), except in competition weeks where no strength session was done. For the rest of the season (last ve weeks), they only performed one day of explosive strength. Concerning the training session, two exercises were done in each workout, one for the upper body (pull-up or bench press) and another for the lower body (squat, deadlift or hip thrust). Mobility exercises were also included in the warm-up for the swimming and resistance sessions, and also for the running sessions (only when intense sessions were carried out at or above the second ventilatory threshold). 2.2. Procedures 2.2.1. Study Protocol Before starting the elite national triathlon season, the triathletes rested for two full weeks between the previous and current season. During the rst month, all triathletes took part in a mesocycle of adaptation according to the principles of progression and super- compensation training (three weeks of training load and one week of recovery). During this adaptation mesocycle, the triathletes performed four microcycles of 15%, 20%, 25% and 15% of the peak load microcycle of the season along the rst, second, third and fourth week, respectively. The running pre-test took place in the last week of this adaptation mesocycle. After 29 weeks of training, the running post-test was performed. Three main training intensities were de ned according to the three main training zones de ned for this study: ventilatory threshold 1 (VT1) (zone 2), ventilatory threshold 2 (VT2) (zone 4)

Appl. Sci.2021,11, 1050 4 of 12 and maximal aerobic speed (MAS) (zone 6) [30]. These training zones were subdivided into further training zones for daily training. All participants trained with eight individual training zones [31] to be more precise in some workouts and to use the “objective load scale” (ECOs) to control the training load. The ECOs were calculated by multiplying the duration (in minutes) of a training session with a scoring value between 1 and 50, depending on the heart-rate-based training zone (1–8) and by a factor of 1.0, 0.75 or 0.5 for running, swimming or cycling, respectively [31]. Indeed, to quantify the individual training load for each triathlete, a speci c test for each discipline was carried out for the swimming and cycling segment. The cycling test was performed in the laboratory; a ramp protocol until exhaustion was used, starting at 50 watts and increasing 5 watts every 12 s [32]. Participants used their own bike; the rear wheel was removed and attached to a Hammer direct drive trainer (CycleOps, Madison, WI, USA). For the cycling test, the same gas-exchange analyzer was used as for the running test (Cosmed ® K4b 2, Rome, Italy). The swimming test was carried out in a 25 m pool performing incremental steps in pace every 200 m using the protocol of 7 200 each 5 min [33]. The determination of training zones was interpreted using lactate samples of each step. Similar to the running test, VT1, VT2 and VO2max were subdivided into further training zones for daily workouts in swimming and cycling disciplines. 2.2.2. Anthropometry An anthropometric method was applied to estimate the body composition of the triathletes. All measurements were taken by the same anthropometrist, Level 3 of the International Society for the Advancement of Kinanthropometry (ISAK) and in the same tent (ambient temperature 22 1 C). The Ross and Marfell-Jones [34] protocol was followed and the measures were taken three times for each subject. The equipment used included a Holtain skinfold calliper (Holtain Ltd., Crymych, UK), a Holtain bone breadth calliper (Holtain Ltd., Crymych, UK), scales, a stadiometer and anthropometric

for the Advancement of Kinanthropometry (ISAK) and in the same tent (ambient temperature 22 1 C). The Ross and Marfell-Jones [34] protocol was followed and the measures were taken three times for each subject. The equipment used included a Holtain skinfold calliper (Holtain Ltd., Crymych, UK), a Holtain bone breadth calliper (Holtain Ltd., Crymych, UK), scales, a stadiometer and anthropometric tape (SECA Ltd., Hamburg, Germany). The physical characteristics of age, weight and stature were measured in that order: age, weight and stature. The biepycondilar humerus, bi-styloid and biepicondylar femur breadths; arm relaxed, arm exed and tense; mid-thigh and calf girths; sub-scapular, biceps, triceps, suprailiac, supraspinal, front thigh and medial calf; and abdominal skinfold measurements were taken. Muscle mass was calculated using the Lee equation [35]. Fat mass was calculated using the Withers equation [36]. Bone mass was calculated using the Döbeln equation, modi ed by Rocha [37]. Somatoype was calculated using the Heath–Carter equations [38]. 2.2.3. Running Test (RT) The incremental running test to volitional exhaustion protocol was used to determine the intensities in running. The running test was performed on a 400-m certi ed track. Participants started at 10 km/h and increased 0.3 km/h every 200 m [39]. The test was conducted using a gas-exchange analyzer (Cosmed ® K4b 2, Rome, Italy). All runners performed the maximal test with running shoes between 250 and 300 g weight for each shoe. Participants used the Stryd Summit Footpod (Stryd, Boulder, CO, USA) attached to the runner's right shoelace equidistant from the participant's malleolus and the toe of their shoe; the device was connected to a Garmin Fenix 3 hr watch and recorded data each second. The following variables were measured during the tests: oxygen uptake (VO2), ventilation (VE), ventilatory equivalents for oxygen (VE VO2 1) and carbon dioxide (VE VCO2 1), as well as the end-tidal partial pressure of oxygen (PETO2) and carbon dioxide (PETCO2). Maximal oxygen uptake (VO2max) was recorded as the highest VO2value obtained for any continuous 1-min period. VT1 was determined based on the criteria of an increase in both (VE VO2 1) and (PETO2) with no increase

oxygen (VE VO2 1) and carbon dioxide (VE VCO2 1), as well as the end-tidal partial pressure of oxygen (PETO2) and carbon dioxide (PETCO2). Maximal oxygen uptake (VO2max) was recorded as the highest VO2value obtained for any continuous 1-min period. VT1 was determined based on the criteria of an increase in both (VE VO2 1) and (PETO2) with no increase in (VE VCO2 1); whereas VT2 was determined using the criteria of an increase in both (VE VO2 1) and (VE VCO2 1), and a decrease in (PET CO2). Two independents observers identi ed VT1 and VT2 and in case

Appl. Sci.2021,11, 1050 5 of 12 of disagreement, the opinion of a third researcher was sought [40]. Heart rate (HR) was continuously monitored during the test using radiotelemetry (Polar Electro ® , Kempele, Finland). The maximal aerobic speed (MAS) was determined as the speed associated with the VO2max during the test, as well as the velocity and power linked with the ventilatory thresholds. The same procedure was used to determine the biomechanical parameters linked to the MAS and ventilatory thresholds. The following spatial variables were analyzed through the Stryd “Power Center” on the Stryd application: stiffness, measured in kilonewtons per meter (kn/m); contact time (CT), measured in milliseconds (ms); vertical oscillation (VO), measured in centimetres (cm); and cadence, measured in steps per minute (spm). The values of the spatiotemporal parameters were averaged over the steps of the same test speed, for at least 30 s. From the recorded contact and ight times was obtained the variable “duty factor”, which is the quotient between the contact time and the total step time [18]. In the same way as in previous investigations, to compare subjects of a different stature, the step amplitude was normalized, dividing it by the height of the trochanter [18]. For ying time (FT), measured in seconds (s), and step length (SL), measured in meters, the same procedure of Garc½a Pinillos et al. [25] was used, as follows: FT (s) = step time (s) CT (s) where step time is the time from the beginning of the step cycle (take-off) to the end (previous frame to take-off). Step time (s) = 60/SF (steps/min). SL (m) = running velocity (m min 1 )/SF (steps/min) 2.3. Statistical Analyses Data are presented as the mean and SD. Normality tests were used to study all the dependent variables (Shapiro–Wilk). After the parametricity of the sample was con rmed, a within-subject repeated measures design was used to assess the changes in anthropometric, physiological and biomechanical parameters. Signi cance was established atp< 0.05. The magnitude of differences or effect sizes (ESs) were calculated according to Cohen's d [41] and interpreted as small (0.2 < ES

This study analyzes biomechanical changes in elite triathletes over 29 weeks of training.