Abstract
/Objectives: The aim of this study was to investigate the acute effect of isometric and plyometric combined activation prior to the endurance performance assessed with the 30-15 Intermittent Fitness Test (30-15 IFT) and cardiovascular parameters.Methods: In this crossover study the data of 14 elite female soccer players aged 22.1±2.9 years were assessed. The conditioning activity (CA) consisted of three sets of five seconds of maximal mid-thigh pull (IMPT), and peak force was measured, and four countermovement jumps were performed. Contact time, jump height, and reactive strength index (RSI) were assessed. Ninety seconds of rest between the sets was performed. Then, 7 min after the CA, the 30-15 IFT was performed.Results: One-way repeated measures (RM) ANOVA showed that performance during the CA did not decrease; what is more, it improved in RSI (p< 0.01). Further, paired samplest-test showed that the performance in the IFT did not change, whereas training impulse (TRIMP) was increased after CA (p= 0.039, ES = 0.61), thus the Bayesian paired test yielded only anecdotal evidence in favor of the alternative hypothesis (BF10= 1.92; error = 2%).Conclusions: The improvement in CA suggests potentiation rather than fatigue. However, the unchanged performance alongside a modest TRIMP increase should be interpreted with caution, as TRIMP alone provides a limited assessment of physiological cost. Therefore,
CA (p= 0.039, ES = 0.61), thus the Bayesian paired test yielded only anecdotal evidence in favor of the alternative hypothesis (BF10= 1.92; error = 2%).Conclusions: The improvement in CA suggests potentiation rather than fatigue. However, the unchanged performance alongside a modest TRIMP increase should be interpreted with caution, as TRIMP alone provides a limited assessment of physiological cost. Therefore, while the applied protocol did not enhance endurance performance, further research using multiple physiological markers is needed to clarify its impact on internal load and overall efficacy. Keywords:endurance; heart rate; zones; conditioning activity; isometric; plyometric 1. Introduction Female football has experienced rapid growth in recent years, accompanied by in- creasing physical demands placed on athletes [1]. Among the key determinants of on-field performance is aerobic and intermittent endurance capacity, which underpins repeated high-intensity efforts throughout a match [2]. In this context, methods to optimize acute performance or physiological efficiency during endurance tasks are of particular relevance for elite female athletes [3]. One such method for acute effects is post-activation performance enhancement (PAPE), a phenomenon in which muscular performance is transiently improved following a high- intensity conditioning activity (CA) [4–6]. Although traditionally studied in the context of explosive tasks (e.g., jumps, sprints), recent investigations have begun to explore whether Physiologia2025,5, 25 https://doi.org/10.3390/physiologia5030025
Physiologia2025,5, 25 2 of 13 PAPE may also benefit endurance-based activities [7,8]. The premise is that an appropri- ately selected CA may improve neural drive, tendon stiffness, or muscle temperature— potentially enhancing running economy or reducing cardiovascular strain during prolonged efforts [4,9]. Despite the growing interest in PAPE-based warm-up protocols among elite football teams, their use in women’s soccer remains limited and largely unstandardized. A recent randomized controlled trial conducted on highly trained female football players reported no significant acute benefits on sprint or change-of-direction performance following a potentiation warm-up involving jumps and COD drills [10]. These findings underscore that directly translating activation protocols from men’s football may not yield expected results in female athletes, and in some cases may even induce transient fatigue. While PAPE principles are increasingly explored in elite sports, robust evidence supporting their effectiveness in women’s football is still lacking [11]. However, most PAPE studies have focused on short maximal efforts (<10 s). For instance, highly trained boxers performing Wingate tests showed elevated post-test heart rate, perceived exertion, and blood lactate after CA protocols [9], suggesting that cardio- vascular parameters are indeed influenced by CA. This raises an important question: can CA improve endurance without imposing undue cardiovascular stress? While PAPE is widely documented for explosive movements, its relevance to endurance performance remains debated. The recent systematic review and meta-analysis by Vasconcelos et al. [12] demonstrated only a very small and inconsistent effect (SMD = 0.15) of PAPE on endurance tasks, with low certainty of evidence, suggesting that its ergogenic potential in this domain is uncertain. Moreover, the mechanisms typically associated with PAPE—such as increased neural drive, transient phosphorylation of the myosin regulatory light chain, and improved tendon stiffness—have not been conclusively linked to enhanced outcomes in endurance tests that predominantly rely on aerobic and anaerobic metabolism [13]. This gap highlights the need for studies exploring whether neuromuscular enhancements induced by CA can translate into improved efficiency during intermittent endurance activities. The existing literature is also limited regarding female athletes. Most PAPE stud- ies have either excluded women or generalized findings from male-dominated samples, despite evidence
in endurance tests that predominantly rely on aerobic and anaerobic metabolism [13]. This gap highlights the need for studies exploring whether neuromuscular enhancements induced by CA can translate into improved efficiency during intermittent endurance activities. The existing literature is also limited regarding female athletes. Most PAPE stud- ies have either excluded women or generalized findings from male-dominated samples, despite evidence that hormonal modulation and muscle fiber composition may influ- ence potentiation responses [14]. Female athletes, particularly those in soccer, present unique physiological profiles that could alter the potentiation–fatigue balance. Conse- quently, investigating their specific responses to CA is crucial for developing evidence- based warm-up strategies. Finally, contemporary warm-up practices in elite sports emphasize individualized micro-activation and priming routines to optimize readiness [15]. These strategies integrate both neuromuscular and cardiometabolic stimuli, aligning with the potential benefits sought through CA. However, whether such protocols enhance intermittent endurance while avoiding excessive cardiovascular cost remains unresolved. Therefore, the present study addresses this gap by evaluating the acute effects of a combined isometric–plyometric CA on endurance performance and cardiovascular strain in elite female soccer players. In endurance contexts, isometric and plyometric exercises are promising candidates; thus, to date, not many studies have verified this, and some data for sprint running were provided [16]. Isometric mid-thigh pull (IMTP) permits high-force output in a fixed position, while plyometrics harness the stretch–shortening cycle and enhance tendon stiff- ness [17,18]. When combined, these modalities may potentiate both neural activation and elastic mechanics—potentially improving running economy and cardiovascular efficiency during intermittent exertion such as the 30-15 Intermittent Fitness Test(30-15 IFT), a typ- ical assessment of endurance in soccer [19]. Notably, chronic training studies, such as
Physiologia2025,5, 25 3 of 13 those comparing isometric and plyometric training, have reported improvements in run- ning economy and aerobic performance, although acute cardiovascular responses remain underexplored [9,17]. Assessing cardiovascular parameters—particularly heart rate and training impulse (TRIMP)—is important because an elevated heart rate during or after endurance exercise can indicate increased physiological cost, even when performance remains unchanged [20]. Despite theoretical and mechanistic support, empirical evidence on whether combined isometric and plyometric CA can effectively enhance intermittent endurance performance in elite female soccer players is limited. Furthermore, understanding the trade-off between performance benefits and cardiovascular costs is essential for practical applications. There- fore, the aim of this study was to investigate the acute effects of a combined isometric and plyometric CA on endurance performance (measured via the 30-15 IFT) and cardiovascular strain (via heart rate/TRIMP) in elite female soccer players. 2. Materials and Methods 2.1. Study Design This investigation employed a randomized crossover design consisting of three ses- sions separated by a 7-day interval to ensure full recovery and minimize potential carryover effects. The first session included body composition assessment and familiarization with the conditioning activity (CA). The familiarization session consisted of a complete walk- through of the CA protocol, performance of several submaximal and maximal IMTP trials, and execution of Countermovement Rebound Jump (CMRJ) on the measurement devices. Additionally, the structure of the 30–15 IFT was explained, and players completed a short- ened version of the test to ensure they were accustomed to the pacing and turning demands. This familiarization was designed to minimize learning effects and improve measurement reliability. Participants were randomly assigned to two testing sequences (Group A and Group B) using an online randomization tool (www.randomizer.org). Group A completed the 30–15 IFT with the conditioning activity (CA) in the second session and without the CA in the third session, while Group B performed the sessions in the opposite order. This counterbalanced approach was implemented to minimize potential order effects. The experimental sessions were separated by 7 days to ensure full recovery and to reduce the likelihood of carryover effects. The 7 min interval between the CA
(CA) in the second session and without the CA in the third session, while Group B performed the sessions in the opposite order. This counterbalanced approach was implemented to minimize potential order effects. The experimental sessions were separated by 7 days to ensure full recovery and to reduce the likelihood of carryover effects. The 7 min interval between the CA and the 30–15 IFT was selected based on previous findings indicating that PAPE effects typically occur within a 4–10 min window following activation, depending on the intensity and type of exercise used [21]. This interval was chosen to align with the expected potentiation window while minimizing the risk of residual fatigue. In the second and third sessions, participants completed the 30-15 Intermittent Fitness Test (30-15 IFT): once following the CA protocol and once without it, with the order of conditions reversed between groups. 2.2. Participants The study sample was selected using a purposive sampling approach to ensure a high level of homogeneity in terms of athletic performance and training background. All participants competed at a similar performance level and were members of the same football club, which minimized potential confounding variables related to differences in coaching methods, training load, or session structure. This approach enhanced the internal consistency of the sample and allowed for more accurate interpretation of the results in the context of the applied experimental protocol. However, this strategy inherently limited the potential sample size from the outset. Considering the exclusion of goalkeepers and the occurrence of injuries, the final sample consisted of 14 field players.
Physiologia2025,5, 25 4 of 13 The initial sample included twenty-four female football players aged 16–28 years (mean age: 22 years), all of whom trained at the 1KS´Sl˛eza Wrocław club and competed in the second-tier national league in Poland (Orlen I Liga Kobiet). Each player participated in approximately six training sessions per week: four technical-tactical football sessions and two strength and conditioning sessions supervised by a performance coach. All participants had at least eight years of football experience. Goalkeepers and players with recent or ongoing injuries were excluded (n= 10). Testing occurred during the final phase of preseason preparation. A post hoc sample size analysis for the applied statistical approach, with a power of 0.80 and an alpha level of 0.05, indicated an effect size of 0.58. 2.3. Body Morphology Stature was measured with a standard anthropometer (Swiss Anthropometer, GPM Anthropological Instruments, DKSH Ltd., Zürich, Switzerland), while body mass was assessed using the InBody230 device (InBody Co., Ltd., Cerritos, CA, USA), which has demonstrated good reliability [22]. Participants stood barefoot, heels together, in an up- right posture with their head aligned in the Frankfort horizontal plane. Body height and weight were recorded to the nearest 0.1 cm and 0.1 kg, respectively. Measurements adhered to the protocols established by the International Society for the Advancement of Kinan- thropometry (ISAK) [23]. Participants were instructed to refrain from consuming food or engaging in strenuous activity for at least 3 h prior to measurement and to empty their bladders immediately before testing. BMI was calculated using the formula: body mass [kg]/height 2 [m 2 ]. 2.4. Isometric Mid-Thigh Pull (IMTP) The isometric mid-thigh pull (IMTP) was assessed using the Muscle Meter, a handheld dynamometer (MAT Assessment, UK) designed to measure isometric force production in field-based conditions. The device features a compact force transducer connected via cable to a digital handheld unit, which provides real-time force output and stores peak values. The device was equipped with adjustable straps and handles to ensure standardized testing across subjects and to secure positioning during maximal efforts. Participants performed the test in a standing position, with the dynamometer anchored between
conditions. The device features a compact force transducer connected via cable to a digital handheld unit, which provides real-time force output and stores peak values. The device was equipped with adjustable straps and handles to ensure standardized testing across subjects and to secure positioning during maximal efforts. Participants performed the test in a standing position, with the dynamometer anchored between the floor and set at mid-thigh level, mimicking a typical pulling posture. The bar height was individually adjusted to maintain sport-specific joint angles at the hip and knee. Lifting straps were used to eliminate grip fatigue and allow force transfer to be focused through the lower and upper limbs. The maximal effort trials consisted of three 5 s pulls. A standardized verbal countdown (“3, 2, 1, pull”) preceded each attempt, and participants received strong verbal encouragement. Pre-tension was allowed solely to remove slack in the system [24]. The device recorded peak isometric force (PF), which was defined as the highest force output displayed during the 5 s maximal effort. 2.5. Countermovement Rebound Jump (CMRJ) The countermovement rebound jump (CMRJ) was assessed using a validated contact platform (Chronojump, Barcelona, Spain), which recorded flight time and subsequently es- timated jump height (JH) using the equation: JH = (9.81×flight time 2 )/8. The Chronojump system has demonstrated excellent reliability (α= 1.00; CV = 4.28±1.95%) and sensitivity, with a smallest worthwhile change (SWC) of 1.3 cm and a typical error (TE) of 0.29 cm, resulting in a signal-to-noise ratio of 4.5 [25]. The Chronopic device, operating at a 1000 Hz sampling rate, connected the contact mat to the measurement software. Participants began in an upright position with feet shoulder-width apart and hands on hips. After a rapid countermovement to approximately 90 ◦ knee flexion, they performed a maximal vertical jump. Upon landing, they were instructed to immediately execute another jump, aiming
Physiologia2025,5, 25 5 of 13 for maximum height with minimal ground contact. Each trial consisted of a continuous series of four consecutive jumps. During each jump, participants were required to keep their legs extended in flight and to land simultaneously on both feet. 2.6. Conditioning Activity (CA) The CA protocol included a 5 s IMTP followed by four repeated CMRJ attempts, focusing on maximal jump height and minimal ground contact time. Three sets were performed with 90 s passive rest intervals between them. Seven minutes post-CA, the 30-15 IFTwas initiated. The interval between CA and the endurance test was set at 7 min to coincide with the expected time window where potentiation effects could still be expressed while minimizing the risk of residual fatigue. Previous studies on PAPE protocols have demonstrated that optimal performance responses are often observed within 4–10 min post-activation, depending on the exercise modality and athlete characteristics [21]. 2.7. 30-15 Intermittent Fitness Test (30-15 IFT) All players were previously familiar with the 30-15 IFT, which was conducted as standard during testing protocols. The test involved 30 s shuttle runs interspersed with 15 s recovery intervals. The initial speed was set at 8 km/h and increased by 0.5 km/h every 30 s [19]. Participants ran between two 40 m lines, adjusting pace based on auditory signals. During rest periods, participants walked forward to the nearest line to begin the next stage. The test has shown excellent reliability (ICC = 0.96) [19]. Final running velocity (VIFT) was recorded as the highest fully completed stage. 2.8. Preparation for the 30–15 IFT Test and Its Placement Within the Training Cycle This study was conducted during the transitional period of the competitive football season, covering two microcycles following an intensive start phase. The 30–15 Intermittent Fitness Test (30–15 IFT) was performed twice: first at the end of the first transitional microcycle (March 30), and again at the end of the second transitional microcycle (April 6). The tests were scheduled after several days of moderate-intensity training sessions to optimize the players’ readiness for high-intensity intermittent exertion and to minimize fatigue-related interference. The players’
The 30–15 Intermittent Fitness Test (30–15 IFT) was performed twice: first at the end of the first transitional microcycle (March 30), and again at the end of the second transitional microcycle (April 6). The tests were scheduled after several days of moderate-intensity training sessions to optimize the players’ readiness for high-intensity intermittent exertion and to minimize fatigue-related interference. The players’ physical preparation included a comprehensive warm-up based on the RAMP model (Raise–Activate–Mobilize–Potentiate), supplemented with an individ- ual preparatory component (“individual prep”). This preparatory block consisted of 1–2 selectedexercises targeting three key areas—ankle, knee, and hip/gluteregion—performed in one set of 6–10 repetitions per side. The “Raise” phase included general movement-based drills such as runs with arm swings, jumps, skips, lateral movements, and lunges. The “Activate” phase involved isometric contractions combined with stretching for the major lower-body muscle groups, while the “Mobilize” phase included dynamic and ballistic stretching exercises. The final “Potentiate” phase comprised speed and reactivity drills such as high-tempo skips, short accelerations, and bounding movements to stimulate neuromuscular readiness for maximal effort. This comprehensive warm-up protocol was intended not only to raise muscle temper- ature and activate motor units but also to elicit appropriate neuromuscular stimulation prior to the submaximal and maximal efforts characteristic of the 30–15 IFT. 2.9. Heart Rate Zones and Training Impulse (TRIMP) Heart rate (HR) was monitored throughout to determine HR maximum, HR mean, and HR minimum. The time spent in specific HR zones was recorded as zone 1: 50–60% HRmax; zone 2: 60–70% HRmax; zone 3: 70–80% HRmax; zone 4: 80–90% HRmax; zone 5: 90–100% HRmax. Training load was quantified using Banister’s TRIMP model [26],
Physiologia2025,5, 25 6 of 13 which incorporates training duration and HR reserve: TRIMP = t×∆HR×y, where ∆HR = (HR_avg−HR_rest)/(HR_max−HR_rest) , where t is the effort duration (min- utes) and y is a sex-specific weighting factor, 0.86×eˆ (1.67×∆HR). TRIMP values were expressed in arbitrary units. The used device was Polar H10 (Polar Electro Oy, Kempele, Finland). The device has confirmed validity [27]. 2.10. Statistical Analysis Normality was assessed using the Shapiro–Wilk test. Data were expressed as mean±SD , with 95% confidence intervals (CI). Homogeneity and sphericity were verified using Levene’s and Mauchly’s tests. A one-way ANOVA repeated measures ANOVA (time) was conducted to verify potentiation effects of conditioning activity. Effect sizes were calculated using partial eta-squared (η 2p), interpreted as small (≤0.01), medium (≤0.06), or large (≥0.14) A paired samplet-test was performed to assess the effects of CA on endurance performance, and the within comparison with effect sizes was reported as Cohen’s d (small≤0.2; medium≤0.79; large≥0.8) [28]. Subsequently, a Bayesian paired samplest-test was conducted using a default symmetric Cauchy prior centered at 0 with a scale of r = 0.707, as recommended by Rouder et al. [29]. This prior width balances sensitivity and conservatism in hypothesis testing and is commonly adopted as a default in applied research. A sensitivity analysis across the range r∈[0.3; 1.0] was also performed to verify the robustness of conclusions. For clarity, the Bayes factor (BF10) represents the ratio of the likelihood of the data under the alternative hypothesis (H1) to that under the null hypothesis (H0). BF10> 1 indicates evidence favoring H1, whereas BF10< 1 supports H0. Conventionally, values of BF10between 1 and 3 are interpreted as anecdotal evidence, 3–10 as moderate evidence, 10–30 as strong evidence, and values > 30 as very strong evidence in favor of H1[30]. Conversely, BF10between 0.33 and 1 indicates anecdotal evidence for H0, 0.1–0.33 moderate evidence, and <0.1 strong evidence supporting H0. All statistical analyses were performed using Jamovi software (version 2.2.2, Jamovi, Sydney, Australia). Ap-value of <0.05 was considered statistically significant. 3. Results In Table morphology, and heart rate parameters are presented. Table 1.Descriptive statistics of study participants. Variable
favor of H1[30]. Conversely, BF10between 0.33 and 1 indicates anecdotal evidence for H0, 0.1–0.33 moderate evidence, and <0.1 strong evidence supporting H0. All statistical analyses were performed using Jamovi software (version 2.2.2, Jamovi, Sydney, Australia). Ap-value of <0.05 was considered statistically significant. 3. Results In Table morphology, and heart rate parameters are presented. Table 1.Descriptive statistics of study participants. Variable Mean ±SD (95%CI) Age [years] 22.1 ±2.9 (20.5–23.8) Body height [m] 1.7 ±0.1 (1.7–1.7) Body weight [kg] 64.2 ±5.4 (61–67.3) BMI [kg/m 2 ] 22.2±1.6 (21.3–23.1) HR max [beats] 194 ±5.1 (191.1–196.9) HR min [beats] 60.9 ±7 (56.8–64.9) HRreserve [beats] 132.7 ±9.3 (127.4–138.1) Training experience [years] 9.9 ±1.7 (8.8–10.9) Abbreviations: SD—standard deviation; 95%CI—confidence interval; BMI—body mass index; HR max— maximum heart rate; HR min—minimum heart rate; HRreserve—heart rate reserve. In the first step of the analysis, a one-way (time) repeated measures ANOVA was performed to assess the immediate effect of conditioning activity to assess the fitness status. Results indicated a lack of decrease in ability to force production as well as in jump height
Description
This study examines the effects of conditioning activities on endurance performance in elite female soccer players.