Processing metadata

The aerobic adaptations of sprint interval training (SIT) and anaerobic adaptations of plyometric training (PT) are well documented in the literature. Bidirectional SIT (including forward and backward “all-out” runs with change of direction) is a new approach to target aerobic and anaerobic traits in football players. Objective: This study intended to evaluate and compare the efficacy of bidirectional SIT versus PT on aerobic parameters, anaerobic parameters and sport-specific skill in university-level football players. Methods: In this two-arm randomized clinical trial, 26 university-level male football players (age 20.88 ± 1.69 years, height 173.70 ± 6.17 cm, mass 66.41 ± 7.60 kg, body mass index 22.04 ± 2.62 kg/m 2 ) were divided into two groups, bidirectional SIT (n = 13) and PT (n = 13, dropout of 1 subject during intervention) groups, respectively. Lower limb power (vertical jump height), sport-specific skill (wall volley), speed, agility, maximum oxygen consumption and running economy at 8, 10, and 12 km/h were analysed before and after four weeks of training. Results: The result revealed that the time effect was significant for all the parameters, while time × group interaction was significant for all variables except running economy, speed and wall volley. However, there is no significant group effect for all variables. Conclusions: Findings suggest that four weeks of bidirectional SIT results in significant improvement in aerobic as well as anaerobic parameters in football players. Therefore, bidirectional SIT can be used as a substitute for PT for anaerobic adaptations with added aerobic benefits in football players. Keywords: maximal oxygen consumption, running economy, agility, vertical jump height, speed, wall volley ACTA GYMNICA, 2025, Volume

Findings suggest that four weeks of bidirectional SIT results in significant improvement in aerobic as well as anaerobic parameters in football players. Therefore, bidirectional SIT can be used as a substitute for PT for anaerobic adaptations with added aerobic benefits in football players. Keywords: maximal oxygen consumption, running economy, agility, vertical jump height, speed, wall volley ACTA GYMNICA, 2025, Volume 55, Article e2025.006 https://doi.org/10.5507/ag.2025.006 Introduction Football is one of the world’s most popular team sports. It is a complex, intermittent and long-duration sport which requires low and high intensity activities intermit- tently during a match as the football players are required to repeatedly and intermittently perform strides, turns, sprints and jumps, which places considerably high aero- bic and anaerobic demands on their body (Bangsbo et al., 2006). Strength, power and their derivatives (acceleration and velocity) required for turning, sprinting and jump- ing make an important contribution to the performance potential and success of football players (Stølen et al., 2005). Footballers also require high aerobic fitness or high endurance for prolonged energy production throughout the game (Hoff & Helgerud, 2004). High aerobic fitness helps in recovery during high-intensity intermittent activi- ties (Helgerud et al., 2001). Apart from the anaerobic and aerobic traits, a footballer also requires sport-specific skills to succeed (Stølen et al., 2005). Sprint interval training (SIT), defined as “all-out” short-duration sprints with long, almost complete recov- ery in between, is a form of maximal or supramaximal OPEN ACCESS

2A. Saif et al. Acta Gymnica, 2025, 55, e2025.006 context of this paper is defined as running in a reverse direction where movement is accomplished via a single leg of support throughout foot–ground contact and both feet simultaneously in the air between contralateral foot strikes. During backward running, an athlete must rely on alterna- tive sensory information due to a lack of visual guidance, which can in turn lead to better performance (Uthoff, Oli- ver, Cronin, Harrison, & Winwood, 2018). Plyometric training (PT) is a form of explosive strength training using explosive movements to develop power involving stretch-shortening cycle (SSC; Markovic et al., 2007). PT contributes to improvement in vertical jump performance, acceleration, agility, leg strength, muscular power, an increase in joint awareness and overall sport-spe- cific skills (Wang & Zhang, 2016). However, although PT has been shown to increase performance variables in many sports, little scientific information is currently available to determine whether PT actually enhances skill performance in football players, considering that football is an extremely demanding sport (Wang & Zhang, 2016). Plyometric training does not always necessarily show improvement in VO 2max . Still, some studies show that plyometric training led to the improvement of endurance performance that could be attributed to the improved RE, which is a result of improved musculotendinous stiffness (Sedano et al., 2013). SIT is explosive, involves SSC and has shown similar neuromuscular adaptations as PT (Lum et al., 2019), while in combination with COD and backward running, the authors expected it to be more efficient in providing the anaerobic adaptation along with the aerobic adaptations. Though literature exists regarding the comparison between the PT and intermittent sprint training on the endurance performance (Lum et al., 2019), no study empirically compares bidirectional SIT against PT on various aerobic parameters, anaerobic parameters and sport-specific skills in football players. Therefore, the study proposes a per- formance-based analysis of the effect of bidirectional SIT and PT on aerobic parameters, anaerobic parameters and sport-specific skills in university football players after four weeks of training. The authors hypothesized that there will be a statistically significant difference between the

against PT on various aerobic parameters, anaerobic parameters and sport-specific skills in football players. Therefore, the study proposes a per- formance-based analysis of the effect of bidirectional SIT and PT on aerobic parameters, anaerobic parameters and sport-specific skills in university football players after four weeks of training. The authors hypothesized that there will be a statistically significant difference between the effect of bidirectional SIT and PT on aerobic parameters, anaerobic parameters and sport-specific skills. Methods Participants The numbers of participants were determined using G*Power (Version 3.1.9.2; https://www.psychologie.hhu. de/arbeitsgruppen/allgemeine-psychologie-und-arbe- itspsychologie/gpower) based on the data representing the changes in running economy following PT in the study of Lum et al. (2019). Thirteen participants per group (includ- ing 10% drop out) were shown to be necessary based on the given effect size of 0.3, α level of .05 and power (1 – β) of .80. A sample of 26 male collegiate university-level football players (age 20.88 ± 1.69 years, height 173.70 ± 6.17 cm, mass 66.41 ± 7.60 kg, body mass index 22.04 ± 2.62 kg/m 2 ) with VO 2max more than 45 ml/kg/min were recruited. Players (aged 18–28 years) with a background of two or more years of systematic football training (> 11 hours per week) and competitive experience and fulfilling basic criteria for lower extremity plyometric pre-training requirements (Davies et al., 2015) with no musculoskeletal injury in the lower limb within six months were included in the study. Exclusion criteria included Physical Activity Readiness Questionnaire Plus score of more than 1, bidi- rectional SIT or PT experience in the previous six months, participation in other competitive sport activity aside from football during the intervention period, history of lower limb or spine surgery and/or systemic or inflammatory dis- eases, acute systematic infection, concussion, head trauma or spine injury. Research procedures in the present study were per- formed in conformity with the Declaration of Helsinki, 1964 and its later amendments. Participants were explained the purpose, methodology, and possible risks of the study, and they were given and signed the informed consent form explaining their rights as research participants. The study is also

infection, concussion, head trauma or spine injury. Research procedures in the present study were per- formed in conformity with the Declaration of Helsinki, 1964 and its later amendments. Participants were explained the purpose, methodology, and possible risks of the study, and they were given and signed the informed consent form explaining their rights as research participants. The study is also approved by the Institutional Ethics Commit- tee of Jamia Millia Islamia (proposal no. 31/10/187/JMI/ IEC/2018). Protocol For this, two-arm comparative randomized clinical trial, the authors examined and compared the effects of four weeks of bidirectional SIT and PT in university-level foot- ball players, as there are only healthy participants and the effects of PT and directional SIT are well documented in literature, each group served as a comparative control for the other. This design allowed for a direct evaluation of the relative effects of each intervention. The participants were randomly assigned into two groups, bidirectional SIT (n = 13) and PT (n = 13), using computer-generated block num- bers, and the participants were trained 2–3 times weekly. There was a total of 10 exercise sessions performed under supervision with at least a 36–48 hour gap between two consecutive sessions. The aerobic performance parameters (running economy and VO 2max ), the anaerobic performance parameters (vertical jump height, speed, agility) and sport- specific skills (wall volley) were investigated in both groups at baseline and after four weeks of training. One participant dropped out of the PT group due to noncompliance with no study-related reason, whereas all the SIT group partici- pants completed the study. All tests were done at the same time of the day to give participants time to rest properly and recover. The study was performed at the human perfor- mance laboratory and the university sports complex. Outcome measures Running Economy RE was evaluated at 8, 10, and 12 km/h. Participants per- formed a standardized warm-up, consisting of 5 min of running at 8 km/h followed by a 5 min passive recovery. RE was recorded and measured breath by breath via an open circuit metabolic system (PowerLab/8M Metabolic System, ADInstruments,

mance laboratory and the university sports complex. Outcome measures Running Economy RE was evaluated at 8, 10, and 12 km/h. Participants per- formed a standardized warm-up, consisting of 5 min of running at 8 km/h followed by a 5 min passive recovery. RE was recorded and measured breath by breath via an open circuit metabolic system (PowerLab/8M Metabolic System, ADInstruments, Dunegin, New Zealand) with an incremental graded treadmill-based test. The responses

3A. Saif et al. Acta Gymnica, 2025, 55, e2025.006 were recorded continuously using Lab Chart (Version 8; ADInstruments, Dunegin, New Zealand)m sampling at 1000 Hz. They were later analysed as 10-s averages at 8, 10, and 12 km/h for 3 min each, in order to measure the RE. RE was defined by averaging the oxygen uptake values during the last 30 s. Maximal oxygen consumption Maximal oxygen consumption was evaluated with two methods, directly via breath by breath via an open-circuit metabolic system (Powerlab/8M Metabolic System, ADIn- struments Pty Ltd, Castle Hill, Australia) with an incre- mental graded treadmill-based test and indirectly derived by Yo-Yo I Recovery Test 1 (YYIR1). The values derived from YYIR1 are used for analysis, as they include the inter- mittent performance aspect of football. The total distance covered during the YYIR1 (including the last incomplete shuttle) was considered as the test score, and this distance was utilized to estimate VO 2max by the equation proposed by Bangsbo et al. (2008): VO 2max (ml/kg/min) = YYIR1 distance (m) * 0.0084 + 36.4. Vertical jump height and peak power Participants were instructed to jump upright from a 90° knee flexion and perform a vertical jump with arm swing as high as possible. The height of the jump (VJH) was deter- mined using a measuring tape attached to a graph paper on which the ink prints of the middle finger during the jump were recorded. Each subject performed three jumps, and the best score was used to analyse the VJH. This test is considered reliable with intra-class correlation coefficient of .97 (Christou et al., 2006). Peak power was determined by the formula proposed by Lara et al. (2006) using the VJH and body mass of each athlete: Peak power (W) = (62.5 * VJH (cm)) + (50.3 * body mass (kg)) – 2184. Sprint time Two 30-m trials were conducted by the participants, with a 3-min recovery period between them, and the best attempt was used for analysis. The player assumes a staggered stance with the front knee bent at 90°, weight shifted forward, arms positioned oppositely to

power (W) = (62.5 * VJH (cm)) + (50.3 * body mass (kg)) – 2184. Sprint time Two 30-m trials were conducted by the participants, with a 3-min recovery period between them, and the best attempt was used for analysis. The player assumes a staggered stance with the front knee bent at 90°, weight shifted forward, arms positioned oppositely to the legs, and the body lean- ing slightly forward for an explosive push-off at the com- mand. The sprints started with the command “Go” and timed with a high-precision stopwatch (Seiko S141, Seiko, Tokyo, Japan) by the assessor standing on the finish line. Agility The Illinois Agility Test was used to analyse the agility. The participants started the test face down with their hands at the level of their shoulders. The trial began with the “Go” command, and the participants started running as quickly as possible. The trial was completed when the players crossed the finish line without disturbing the cones. The time taken to complete the test was recorded. Every sub- ject performed three trials, and the best score was used for analysis. This test is considered reliable with an intra-class coefficient of .85 (Katis & Kellis, 2009). Sport specific skill Wall volley was used as the sport specific skill. Participants were asked to kick a ball from a distance of 1.83 m from a wall and then trap or kick the ball as many times as possible in a period of 30 s toward a marked box of 1.22 × 2.44 m on the wall. Participants were instructed to avoid the use of their hands. Three repetitions of this test were performed by each subject, and the best attempt was utilized for analy- sis. This test is a highly reliable standard test (intra-class correlation coefficient of .97) for evaluating the skill and accuracy of football players in sport-specific skill assessment (Reilly & Holmes, 1983). Training Participants completed 15 min of warm-up, including jog- ging, active stretching, side shuffles, high knee exercises and butt kicks at the beginning of every training session. At the end of every training session,

highly reliable standard test (intra-class correlation coefficient of .97) for evaluating the skill and accuracy of football players in sport-specific skill assessment (Reilly & Holmes, 1983). Training Participants completed 15 min of warm-up, including jog- ging, active stretching, side shuffles, high knee exercises and butt kicks at the beginning of every training session. At the end of every training session, 10–15 min of cool- down sessions comprising jogging and stretching were also mandated for players. For PT, participants were instructed to perform exercises to maximum effort for each repetition. The protocols used for PT are shown in Table 1, adapted from Wong et al. (2010) and Lum et al. (2019) with dupli- cation avoided. The directional SIT protocol used in this study was adapted from Kelly et al. (2018). The bidirectional SIT consisted of three sets of high-intensity sprints with short recovery periods in between. Each sprint interval covered a total distance of 110 m, incorporating both forward and backward sprints over distances ranging from 5–20 m, with multiple changes of direction (COD). A single set comprised three 110 m sprints, with a 20 s recovery period between runs and a 3 min recovery period between sets (Figure 1; Kelly et al., 2018). Although it was not possible to match the overall training volume due to the differing nature of the training protocols, the authors ensured consis- tency in training frequency (10 sessions in total, performed 2–3 times per week over four weeks), total session duration for both groups, and rest intervals between sets. All other training activities and participation levels were balanced between the groups. Data analysis IBM SPSS Statistics for Windows (Version 21; IBM, Armonk, NY, USA) was used for all analyses. The data was assessed by the Shapiro-Wilk test for the normality of the distribution scores. The demographic characteristics and the baseline criterion measures were compared between the Table 1 Plyometric training protocol Exercise Sets Repetitions Alternate leg bounding 4 10 Single-leg hurdle hop 2 10 per side Double-leg hurdle hop 3 10 Depth jump 3 15 Weighted squat jump 3 15 Double leg lateral hop over

Shapiro-Wilk test for the normality of the distribution scores. The demographic characteristics and the baseline criterion measures were compared between the Table 1 Plyometric training protocol Exercise Sets Repetitions Alternate leg bounding 4 10 Single-leg hurdle hop 2 10 per side Double-leg hurdle hop 3 10 Depth jump 3 15 Weighted squat jump 3 15 Double leg lateral hop over hurdles 2 25 Plyo sit ups (from the second week) 3 10 Note. Rest (passive) intervals between sets were 3 min.

4A. Saif et al. Acta Gymnica, 2025, 55, e2025.006 two training groups using an independent t-test. To test for the difference between the groups after training, a 2 × 2 mixed-model analysis of variance (ANOVA) with group (SIT × PT), time (baseline × post-training) and interaction effect (group × time) was employed. The effect size (ES) for the main effect of trial is reported as partial eta-square statistic (η 2 ) with values of .01, .06, and .14 representing small, medium, and large effects, respectively. The data was also analysed using a paired t-test to analyse the pre to post changes in the various parameters. The ES was calculated using Cohen’s d, with values of < 0.2, 0.2, 0.5, and 0.8 representing small, trivial, and large effects respectively. The level of significance was set at α < .05. The formula used for change was: Change (%) = ((post – pre)/pre) * 100. Results At the baseline, there was no significant difference in the demographic characteristics between the groups and all the variables were found to be normally distributed (Table 2). Both groups were comparable in terms of age, height, mass, and body mass index. No significant difference was found between the groups in VJH, leg power, wall volley, speed, VO 2max , agility, RE at 8, 10, and 12 km/h at baseline thus making the groups comparable. The results of 2 × 2 mixed model ANOVA (exact p values are depicted in Table 2), showed significant main effect for time for all the param- eters. Group × time interaction effect was significant for VJH, leg power, and VO 2max ; no significant group effect was found for any variable (Table 2). The paired t-test showed a significant difference in bidi- rectional SIT in all variables, while the PT group showed significant effect in all variables except VO 2max ; however, the ES was different for both groups in all variables, but they were not significantly different from one another, as shown in Table 3. The improvement was calculated to be 13.06% for VO 2max in the bidirectional SIT group. The