Effects of Running-Specific Strength Training, Endurance Training, and Concurrent Training on Recreational Endurance Athletes' Performance and Selected Anthropometric Parameters

: The present study aimed to verify the effects of running-speci c strength training alone, endurance training alone, and concurrent training on recreational endurance athletes' performance and selected anthropometric parameters. Method: Thirty male recreational endurance runners were randomly assigned using a blocking technique to either a running-speci c strength training group (RSSTG), an endurance training group (ETG), or a concurrent training group (CTG). RSSTG performed three strength-training sessions per week orientated to running, ETG underwent three endurance sessions per week, and CTG underwent a 3-day-per-week concurrent training program performed on non-consecutive days, alternating the strength and endurance training sessions applied to RSSTG and ETG. The training protocol lasted 12 weeks and was designed using the ATR (Accumulation, Transmutation, Realization) block periodization system. The following assessments were conducted before and after the training protocol: body mass (BM), body mass index (BMI), body fat percentage (BFP), lean mass (LM), countermovement jump (CMJ), 1RM (one- repetition maximum) squat, running economy at 12 and 14 km/h (RE12 and RE14), maximum oxygen consumption (VO 2max), and anaerobic threshold (AnT). Results: RSSTG signi cantly improved the

periodization system. The following assessments were conducted before and after the training protocol: body mass (BM), body mass index (BMI), body fat percentage (BFP), lean mass (LM), countermovement jump (CMJ), 1RM (one- repetition maximum) squat, running economy at 12 and 14 km/h (RE12 and RE14), maximum oxygen consumption (VO 2max), and anaerobic threshold (AnT). Results: RSSTG signi cantly improved the results in CMJ, 1RM squat, RE12, and RE14. ETG signi cantly improved in RE12, RE14, VO 2max, and AnT. Finally, CTG, obtained signi cant improvements in BFP, LM, CMJ, 1RM squat, RE12, RE14, VO 2max, and AnT. RSSTG obtained improvements signi cantly higher than ETG in CMJ, 1RM squat, and RE14. ETG results were signi cantly better than those attained by RSSTG in AnT. Moreover, CTG marks were signi cantly higher than those obtained by ETG in CMJ and RE14. Conclusion: Performing a 12-week concurrent training program integrated into the ATR periodization system effectively improves body composition and performance variables that can be obtained with exclusive running-speci c strength and endurance training in recreational runners aged 30 to 40. Running-speci c strength training enhances maximum and explosive strength and RE, whereas exclusive endurance training improves VO 2max, AnT, and RE. Performing concurrent training on non-consecutive days effectively prevents the strength and endurance adaptations attained with single-mode exercise from being attenuated. The ATR periodization system is useful in improving recreational endurance athletes' performance parameters, especially when performing concurrent training programs. Keywords: concurrent training; endurance training; running-speci c strength training; periodization; recreational runner 1. Introduction Several sports require an adequate levels of strength and endurance to perform at optimum level in competitive events. However, successfully combining endurance and strength training represents the highest complexity in exercise prescription [1]. It has often Int. J. Environ. Res. Public Health2022,19, 10773.

Int. J. Environ. Res. Public Health2022,19, 10773 2 of 17 been speculated that concurrent training does not generate the same adaptations as single- mode exercise [1]. Even so, the possible mechanisms whereby concurrent training of both tness components can attenuate strength and endurance adaptations remain unclear [2]. In endurance sports, it has traditionally been thought that cardiovascular capacity is the main limiting factor in sports performance [3]. Therefore, maximum oxygen consump- tion (VO2max) and anaerobic threshold (AnT) have been considered the best indicators to predict athletes' performance [4]. Nevertheless, in reality, endurance athletes with similar VO2max may perform differently in sports competitions. Hence, VO2max could not be the best indicator to predict their racing performance. Nowadays, running economy (RE) and the evaluations that imply assessing the muscular power exerted or the speed reached by an athlete during the VO2max are considered better sports performance indicators [5–7]. In this way, speci c scienti c evidence indicates that combining endurance and strength train- ing generates additional bene ts in terms of athletic performance improvement and injury prevention [8]. These improvements could be related to the following mechanisms [8–13]: (a)Musculotendinous factors: Improved muscle-tendinous stiffness and stretch-shortening cycle properties, conversion of fast-twitch type IIx into more fatigue-resistant type IIa bers, and delayed activation of less-ef cient type II bers. (b)Neuromuscular factors: Improved neuromuscular function and ef ciency, improved intramuscular coordination, motor unit recruitment, and ring frequency. (c)Physical tness components: Improved levels of strength. This allows athletes to apply a lower relative percentage of force, which reduces the contribution of the anaerobic energy system and results in reduced fatigue, maintenance of the required application of strength over a longer period, or appliance of more strength per unit of time. Additionally, peak velocity, speed, maximum aerobic speed, and anaerobic capacity are enhanced. All these enhancements would result in an improved RE. Nevertheless, there are arguments against using concurrent training programs in endurance runners. Vikmoen et al. (2016) and Berryman et al. (2018) [14,15] state that sports requiring high strength levels are opposite in nature to endurance sports in terms of energy metabolism and effort duration. Therefore,

speed, and anaerobic capacity are enhanced. All these enhancements would result in an improved RE. Nevertheless, there are arguments against using concurrent training programs in endurance runners. Vikmoen et al. (2016) and Berryman et al. (2018) [14,15] state that sports requiring high strength levels are opposite in nature to endurance sports in terms of energy metabolism and effort duration. Therefore, developing both tness components simultaneously would result in potential combative adaptations [14–16]. Actually, the main adaptations produced by endurance and strength training are not only different but also opposed: Endurance training adaptations include oxidative enzyme activity increment, mitochondrial and capillary density increment, maintenance or reduction of ber size, and possibly also ber type transformations (Type II into I), modifying the model of recruitment and reducing the muscle contractile capacity [17]. In contrast, strength training is associated with reduced capillary density, oxidative enzymes, and mitochondrial density, reducing the oxidative muscle capacity [10,15]. In this regard, some studies have revealed a certain degree of incompatibility between endurance and strength training [9,18,19]. Thus, maximum voluntary contraction, rate of force development and some adaptations such as maximal strength and VO2max can be attenuated [20]. Similarly, time to exhaustion and mitochondrial density can be reduced [14]. This phenomenon is known as the interference effect or concurrent training effect [11], and the potential interferences can be chronic and acute [2,11]. The reasons why the interference effect occurs are [1,2,11] the mechanism of muscle ber recruitment used, the transformation of fast twitch muscle bers into slow twitch muscle bers, and the functioning of the endocrine system. From the molecular point of view, the simultaneous activation of cellular biomarkers that elicit optimal anabolic and endurance responses is also not possible [11]. Moreover, muscle hypertrophy implies the cross-sectional area increment of muscle bers, which may increase the distance between the capillaries inside the muscle and could negatively impact performance. Even so, in untrained individuals, there is an increase in (or at least a maintenance of) the number of capillaries surrounding each muscle ber, and the capillaries per ber area do not experience modi cations. However, since performing concurrent strength

increment of muscle bers, which may increase the distance between the capillaries inside the muscle and could negatively impact performance. Even so, in untrained individuals, there is an increase in (or at least a maintenance of) the number of capillaries surrounding each muscle ber, and the capillaries per ber area do not experience modi cations. However, since performing concurrent strength and endurance

Int. J. Environ. Res. Public Health2022,19, 10773 3 of 17 training can mitigate the hypertrophic response, and endurance-trained athletes have a greater number of capillaries than untrained athletes, these ndings may not apply to experienced endurance athletes [14]. In line with the existence of arguments for and against the use of concurrent train- ing, some studies have found improvements in sports performance after using strength training in enduranceathletes [6,11] , whereas no bene cial effect was observed in other research [14,21] . The discrepancies between studies may be due to the development of different types of strength, external variables not directly related to the intervention, the use of different training methods [12,22], or the application of training methods lacking scienti c rigor [23]. As a result, it is essential to continue searching for better strategies to improve athletic performance by implementing strength training sessions on endurance training programs and preventing the interference between both tness components [11,16]. Future studies should focus on minimizing the interference effect when concurrent training is applied, and training load organization, type, order, and optimal application are crucial to attain this goal. Further research is also needed to understand better the relationship between strength training, anaerobic metabolism, and endurance sports performance. New studies must be longer in duration, since the greatest increases in RE occur after implementing training protocols of more than 24 sessions, and most of the existing studies are shorter [15]. Moreover, valid strength assessments through a range of different velocities must be used, implementing adequate strength training programs over a long-term intervention period, and using multi-joint strength, explosive-strength, or reactive-strength exercises due to their superior functionally [6]. Future studies must also integrate the intervention design into a suitable periodization system and apply sports training principles to synchronize all training contents [20]. In this respect, to the best of our knowledge, at present, only one investigation has been conducted to verify the effect of strength training on endurance runners by using a periodization system [21]. Additionally, athletes' training programs must be adapted to their personal needs and abilities. Thus, according to the law of

training principles to synchronize all training contents [20]. In this respect, to the best of our knowledge, at present, only one investigation has been conducted to verify the effect of strength training on endurance runners by using a periodization system [21]. Additionally, athletes' training programs must be adapted to their personal needs and abilities. Thus, according to the law of diminishing returns, individuals' ability to attain speci c adaptations will depend on their training level. Less-trained subjects are likely to obtain greater adaptations since they have a greater adaptation reserve. In contrast, well-trained individuals need more demanding training stimuli to attain improvements throughout the training process [22]. Importantly, most existing studies related to concurrent training have focused on verifying the compatibility of simultaneous strength and endurance training. However, very few of them have examined the in uence of strength, and particularly of running- speci c strength training, on endurance performance [24]. Most studies examined the interference of endurance on maximal strength and hypertrophy, but not the opposite [11]. In this context, the utility of strength training remains to be clari ed for endurance athletes, and research ndings are often inconclusive [22]. For this reason, it is necessary to continue investigating this topic [17]. In fact, sports scientists have studied new ways to enhance biomechanics, technique, energy production, sports equipment, injury prevention, and recovery. However, concurrent training and the effect of strength training in endurance athletes is a very complex phenomenon that requires new research. 2. Objective The main objective of the present study was to verify the effect of running-speci c strength training, endurance training alone, and concurrent training on physiological performance and selected anthropometric variables in recreational runners. We also aimed to ascertain if 3-day-per-week concurrent training performed on non-consecutive days attenuates the strength, endurance, and anthropometric adaptations compared to strength and endurance training in isolation.

Int. J. Environ. Res. Public Health2022,19, 10773 4 of 17 3. Materials and Methods A quasi-experimental randomized study was conducted. 3.1. Subjects Thirty male recreational endurance runners participated in the present research. They were assigned into three different groups: a running-speci c strength training group (RSSTG) [age: 34.7 (2.36); height: 1.77 (0.04); weight: 67.05 (5.37); BMI: 21.27 (1.87)], an endurance training group (ETG) [age: 35.1 (2.77); height: 1.78 (0.05); weight: 65.80 (4.38); BMI: 20.68 (1.31)], or a concurrent training group (CTG) [age: 34.3 (2.37); height: 1.76 (0.03); weight: 66.96 (4.48); BMI: 21.48 (1.03)]. RSSTG performed thrice-per-week strength training program orientated to running on non-consecutive days. ETG performed thrice-per-week endurance training on non-consecutive days. Finally, CTG underwent 3-days-per-week concurrent training performed on non-consecutive days. CTG alternated the running- speci c strength training sessions performed by RSSTG and the endurance training sessions underwent by ETG. The inclusion criteria were (a) be an active recreational runner; (b) able to run one km in less than 4:30 min; (c) have practiced running at a recreational level for at least the past ve years before participating in the current research; (d) perform endurance training regularly, with a weekly frequency of not less than three times a week, but no more than ve times a week; (e) have not performed endurance or strength systematic training for the last year leading up to the research's commencement; (f) non-smoker; (g) do not use nutritional supplementation; (h) do not suffer from chronic diseases or ongoing injuries; (i) aged between 30 and 40 years old. Participants were asked not to modify their dietary habits or lifestyle during the intervention process, and attendance was recorded. Subjects were required to attend at least 90% of the training sessions to be included in the study. Similarly, participants were informed that they could voluntarily withdraw from the study at any time. The research was conducted according to the ethical principles of the Declaration of Helsinki. It was approved by the Ethics Commission of Prešov University (Prešov, Slovakia) (ethical clearance number: 2/2021). Similarly, all subjects who participated in this study were required to submit written

the study. Similarly, participants were informed that they could voluntarily withdraw from the study at any time. The research was conducted according to the ethical principles of the Declaration of Helsinki. It was approved by the Ethics Commission of Prešov University (Prešov, Slovakia) (ethical clearance number: 2/2021). Similarly, all subjects who participated in this study were required to submit written informed consent. Previously, they received a verbal and written explanation about the experimental design and the potential risks and bene ts of participating in this research. 3.2. Randomization A blocking design was used to avoid any possible bias when the subjects were allocated into three different experimental groups and to ensure the trial's proper randomization. The blocking factor was the VO2max value obtained through the incremental load test. According to the results obtained in this test, participants were allocated to one of the ten blocks created. Athletes who obtained the best three marks were assigned to block one. Athletes who obtained the fourth, fth, and sixth-best marks were assigned to block two, and so on. Afterward, each block's three members were randomly assigned to one of the three different experimental groups. Therefore, there was one member of each block in each experimental group. 3.3. Training Protocol The intervention lasted 12 weeks, and study participants performed three sessions per week on non-consecutive days. The training protocol was designed using the ATR block periodization system. The training intervention was divided into three mesocycles: accumulation ( rst six weeks), transmutation (from week seven to week 10), and realization (weeks 11 and 12). The duration of the training protocol was the minimum necessary to attain the planned adaptations in accordance with the abilities developed in each mesocycle, the sports discipline, and the characteristics of the athletes. The training methods applied to RSSTG are shown in Table, and the training methods that ETG underwent are shown in Table.

Int. J. Environ. Res. Public Health2022,19, 10773 5 of 17 Table 1.Training methodology that will be used with RSSTG. Week Training Parameters 1 I: 64% 1RM; S: 4; R: 14; RT: 2”; Ex: Squat, leg curl, calf raise 2 I: 69% 1RM; S: 4; R: 12; RT: 2 0 ; Ex: Squat, leg curl, calf raise 3 I: 69% 1RM; S: 5; R: 12; RTS: 2 0 ; Ex: Squat, leg curl, calf raise 4 I: 69%–69%–75%–75%–80% 1RM; S: 5; R: 12-12-10-10-8; RTS: 3 0 ; Ex: Squat, leg curl, calf raise 5 I: 69%–75%–80%–85% 1RM; S: 4; R: 12-10-8-6; RTS: 3 0 ; Ex: Squat, leg curl, calf raise 6 I: 80% 1RM; S: 4; R: 8; RTS: 3 0 ; Ex: Squat, leg curl, calf raise 7 6S of: Squat (6R at 80% 1RM) + hurdle hops (10R) + 2 0 30 00 running at 100% of MAS; RTS: 5 0 8 6S of: Squat (5R at 82% 1RM) + hurdle hops (10R) + 2 0 30 00 running at 100% of MAS; RTS: 5 0 9 6S of: Squat (4R at 84% 1RM) + extended bounds (cover 50 m alternating legs by doing the lowest possible number of strides) + 2 0 15 00 running at 105% of MAS; RTS: 5 0 10 6S of: = Squat (3R at 86% 1RM) + extended bounds (cover 50 m alternating legs by doing the lowest possible number of strides) + 2 0 running at 110% of MAS; RTS: 5 0 11 Uphill running. Di: 200 m; I: 115% of MAS; Incl: 6%; S: 3; R: 5; RTR: 3 0 ; RTS: 10 0 12 Uphill running. Di: 200 m; I: 120% of MAS; Incl: 6%; S: 2; R: 5; RTR: 3 0 ; RTS: 10 0 I: intensity; S: sets; R: repetitions; RTS: resting time between sets; RTR: resting time between reps; 1RM: one- repetition maximum; MAS: maximum aerobic speed; Di: distance; Incl: inclination. Table 2.Training methodology that will be used with ETG. Week Training Parameters 1 Fartlek training. Du: 50 0 ; I: 117–162 b.p.m. 2 Fartlek training.

RTR: 3 0 ; RTS: 10 0 I: intensity; S: sets; R: repetitions; RTS: resting time between sets; RTR: resting time between reps; 1RM: one- repetition maximum; MAS: maximum aerobic speed; Di: distance; Incl: inclination. Table 2.Training methodology that will be used with ETG. Week Training Parameters 1 Fartlek training. Du: 50 0 ; I: 117–162 b.p.m. 2 Fartlek training. Du: 55 0 ; I: 117–162 b.p.m. 3 Fartlek training. Du: 60 0 ; I: 117–162 b.p.m. 4 Continuous training; Du: 55 0 ; I: 135–139 b.p.m. 5 Continuous training; Du: 50 0 ; I: 139–144 b.p.m. 6 Continuous training; Du: 45 0 ; I: 144–149 b.p.m. 7 Extensive interval training (long intervals); I: 159–162 b.p.m.; 10S of 3 0 ; RT: 2 0 8 Extensive interval training (long intervals); I: 162–165 b.p.m.; 10S of 2 0 30 00 ; RT: 2 0 9 Extensive interval training (medium intervals). I: 165–168 b.p.m.; 14S of 1 0 30 00 ; RT: 2 0 10 Extensive interval training (medium intervals). I: 168–171 b.p.m.; 16S of 1 0 ; RT: 2 0 11 Repetition training. I: 180 b.p.m.; 5R of 3 0 . RT: 8 0 12 Competition method. I: 100% of competition running pace; 1R; Di: 3.5 km Du: duration; I: intensity; R: repetitions; RT: resting time; b.p.m.: beats per minute; Di: distance. Likewise, CTG underwent 3-day-per-week concurrent training performed on non- consecutive days, alternating the strength and endurance sessions carried out by RSSTG and ETG. All training sessions were supervised by the same researcher: a One Physical Education Bachelor's Degree holder, expert in sports training, and with more than 20 years of working experience in the sports eld. Likewise, all training sessions were conducted in the same tness center to minimize external variables' in uence avoid compromising the results' validity and.

Int. J. Environ. Res. Public Health2022,19, 10773 6 of 17 3.4. Assessments Physiological and selected anthropometric parameters were measured before (pre- test) and after (post-test) applying the 12-week training protocol. The assessments were conducted after a rest period of 48 h, between 5:00 p.m. and 7:00 p.m. The study participants were asked to refrain from ingesting food or beverages three hours before testing. To avoid the learning effect, a theoretical–practical training session was conducted one week before the pre-test. The main researcher explained the testing protocols in detail. Thereupon, the participants practiced the proper technique of execution of all tests to verify the correct functioning of the equipment and procedures used in the assessment. The following two-phasewarm-up was performed before conducting the physical and physiological tests: General warm-up: 10 min running at 60% of their theoretical maximum heart rate plus ve minutes of joint mobilization exercises. Speci c warm-up: 2 10 vertical jumps, three sets of squats (10 reps at 50% of their estimated 1RM, ve reps at their estimated 70% 1RM, and three reps at their estimated 80% 1RM), and one set of 20 m acceleration. The theoretical 1RM was estimated based on the information collected during the theoretical–practical training session conducted one week before the pre-test. In addition, the subject's BM, age, and strength training experience were also taken into account. Assessments included in the pre-test and post-test are detailed below: Body mass (BM) and body mass index (BMI): Both were measured using a Seca digital column scale, model 769 (Hamburg, Germany). Height was measured to the nearest 0.1 cm and body mass to the nearest 0.1 kg. Body mass and body mass index were assessed by the same investigator, and the subjects were in bare feet. Body fat percentage (BFP): BFP was obtained through the following equation [25]: BFP = [(Sof abdominal, subscapular, triceps, suprailiac, abdominal, thigh, calf)0.143] + 4.56. The plicometer used to measure the fat folds was a Harpenden Skinfold Caliper, model FG1056 (Sussex, UK). Lean mass (LM): LM was calculated by using the following formula: LM =Body Mass (kg) (Fat Mass (Kg) BFP). Countermovement

This research investigates the impact of various training regimens on athletic performance.