The Acute Effects of Combined Isometric and Plyometric Conditioning Activities on Sprint Acceleration and Jump Performance in Elite Junior Sprinters

vestigates the acute effects of a combined isometric and plyometric unilateral conditioning activity (CA) on post-activation performance enhancement (PAPE) in junior elite sprinters. The rationale for combining isometric and plyometric exercises lies in their complementary effects: isometric exercises enhance neuromuscular activation, while plyometric exercises may exploit the stretch–shortening cycle to maximize power output. Thirteen sprinters (10 males, three females) performed countermovement jumps (CMJ) and 50 m sprints before and after the CA protocol, which involved Bulgarian split squats (15% body mass) and single-leg hops. Performance metrics, including sprint times, CMJ height, and modified reactive strength index (RSImod), were recorded and analyzed. Results showed a significant improvement in CMJ height (2.6±3.1%,p< 0.001) and RSI (4.1±7.5%,p= 0.038), alongside a reduction in 20 m sprint time (−0.8±1.4%,p= 0.012). No significant changes were observed in 40 m and 50 m sprint times or ground contact and flight times. These findings suggest that the applied CA selectively enhances sprint acceleration and vertical jumping performance, with a minimal impact on sprint distances above 20 m. This study underscores the potential of incorporating combined

reduction in 20 m sprint time (−0.8±1.4%,p= 0.012). No significant changes were observed in 40 m and 50 m sprint times or ground contact and flight times. These findings suggest that the applied CA selectively enhances sprint acceleration and vertical jumping performance, with a minimal impact on sprint distances above 20 m. This study underscores the potential of incorporating combined isometric and plyometric CAs into sprint training to optimize short-distance performance, though further research is needed to refine exercise protocols and explore long-term effects. Keywords:PAPE; running; muscle stiffness; countermovement jumps 1. Introduction Post-activation performance enhancement (PAPE) refers to a transient improvement in voluntary exercise performance, such as jumping or sprinting, following a high-intensity voluntary conditioning activity (CA) [1,2]. The primary mechanisms underlying PAPE are thought to include the potentiation of specific neuromuscular responses, elevated muscle temperature, and changes in muscle water content following a maximal or submaximal CA [3–5]. Many athletes and strength coaches aim to optimize performance efficiently within a limited number of training sessions. Several studies report that performing under conditions that transiently benefit from potentiating effects may contribute to long-term performance gains over time [6]. Moreover, in elite sports, where marginal performance dif- ferences can determine competition outcomes, incorporating an effective CA immediately preceding competitive performance may be desirable. Appl. Sci.2025,15, 2125 https://doi.org/10.3390/app15042125

Appl. Sci.2025,15, 2125 2 of 11 Isometric muscle contractions are widely utilized in both research and training due to their effectiveness in eliciting PAPE. Common modifications in isometric CA involve adjust- ing variables such as method (overcoming vs. yielding resistance), joint angle, intensity, and contraction duration. However, the optimal distribution of the single repetitions duration in isometric contractions for eliciting the PAPE effect remains unexplored [7,8]. Isometric contractions effectively activate muscles and the nervous system before sprinting [9]. These exercises should primarily target the gluteus, hamstrings, quadriceps, and calf muscles, as they are the key muscle groups driving sprint performance. Additionally, isometric exercises improve stability and enhance neuromuscular efficiency [10]. Isometric holds can increase blood flow to the targeted muscles, thus serving as an additional specific warm-up. Furthermore, isometric activation may enhance mental focus, enabling athletes to better engage the muscles required during specific sprint phases. Another advantage of isometric resistance exercises is their relative safety, as they do not impose excessive stress on the joints. Moreover, isometric holds activate stabilizing muscles, potentially reducing injury risk. However, while isometric exercises effectively activate the prime movers for sprinting, they lack the explosive and reactive engagement essential for sprint performance [11,12]. In contrast, plyometric exercises involve rapid, explosive movements utilizing the stretch–shortening cycle (SSC) (e.g., bounding, squat jumps, skips). These exercises preferentially recruit fast twitch muscle fibers, mirroring the explosive nature of sprinting. Research indicates that plyometric training induces the PAPE effect, enhanc- ing muscle responsiveness and leading to a greater power output (e.g., bounding, box jumps, skipping) [13]. Additionally, plyometric exercises improve muscle elasticity via the SSC, further augmenting explosive sprint performance. Numerous studies confirm the effectiveness of plyometric training in improving sprint performance, primarily due to its biomechanical and neuromuscular similarity to sprinting [9,14]. Specifically, plyometrics appear most beneficial during the early acceleration phase of a 100 m sprint, as they effec- tively stimulate fast-twitch fibers and the nervous system in a highly transferrable manner to sprint mechanics. Several studies have reported that plyometric exercises can enhance voluntary perfor- mance [13,15,16]. Plyometric exercises used as a CA require no specialized

similarity to sprinting [9,14]. Specifically, plyometrics appear most beneficial during the early acceleration phase of a 100 m sprint, as they effec- tively stimulate fast-twitch fibers and the nervous system in a highly transferrable manner to sprint mechanics. Several studies have reported that plyometric exercises can enhance voluntary perfor- mance [13,15,16]. Plyometric exercises used as a CA require no specialized equipment and can be integrated into pre-competition warm-up routines. Numerous studies have exam- ined the effects of jump-based CA on performance outcomes [6,8]. For example, Turner et al. [17] demonstrated that performing three sets of 10 alternate leg bounds (five per leg) with an additional load equivalent to 10% of body mass [BM] significantly improved sprint velocity over 10 m and 20 m, with performance assessed 4 and 8 min post CA. Similarly, Ferreira-Junior et al. [18] confirmed that loaded alternate leg bounds led to reduced sprint split times between 70 m and 100 m among high school track and field athletes. Isometric exercises, which require minimal equipment and induce low levels of fatigue, have also been shown to enhance sprint performance. Krzysztofik et al. [19] demonstrated that a maximal isometric half squat as CA significantly improved 20 m sprint times between the 4th and the 12th minute post CA, as well as 10 m sprint times at the 8th minute. These improvements likely occur through neurological adaptations, including increased motor unit activation, reduced recruitment thresholds, and higher motor unit discharge rates [20]. Importantly, plyometric exercises elicit a stretch reflex, acutely enhancing excitation trans- mission via Ia afferents. This increases the motor neuron pool output, leading to greater higher-order motor unit activation during subsequent activity [21]. Additionally, several physiological mechanisms—such as increased muscle temperature, cellular water content, enhanced muscle activation, and motor pattern adaptations—have been associated with PAPE [5,16]. However, the specific contribution of each factor to the PAPE response remains unclear, warranting further investigation.

Appl. Sci.2025,15, 2125 3 of 11 Therefore, further investigation into potential motor pattern adaptations and the influence of CA execution speed is necessary to determine the optimal exercise selection for eliciting PAPE. The main objective of this study is to determine the effectiveness of unilateral activation through combined isometric and plyometric exercises on sprint performance. 2. Materials and Methods 2.1. Study Design This study utilized a quasi-experimental approach (pre-CA vs. post-CA measure) to examine the effects of a combined isometric and plyometric CA protocol on sprinting and jumping performance in well-trained junior sprinters. The experimental session was conducted on an indoor certified synthetic track, where each athlete completed a standardized warm-up, followed by baseline performance assessments, including the countermovement jump (CMJ) and two 50 m all-out sprints. The activation protocol consisted of Bulgarian split squats with a load equal to 15% of BM, followed by an isometric split squat with the knee flexed at approximately 90 degrees, held for 10 s. Post-CA performance assessments began 8 min after the completion of the CA to evaluate its effect on jumping and sprinting performance. 2.2. Participants Thirteen well-trained junior sprinters (ten males and three females) of the Polish National Team (from 100 to 400 m sprinters) participated in the study (age:18.8±1.6 years ; body mass: 69.4±5.5 kg; body height: 174±8.2 cm; 100 m best time: men10.96±0.41 s , women 12.05±0.31 s). The study was conducted during the pre-season at the end of October 2023. All athletes prepared for the 2024 indoor season and had 8–10 weeks of general conditioning and 3 weeks of specific training behind them at the onset of the research. The tests were performed in an indoor 200 m facility. To minimize fatigue, athletes refrained from intensive exercises 48 h before testing and maintained regular sleep and dietary routines while avoiding supplements and stimulants. The participants received full information about the study procedures, including potential risks, before providing written informed consent to participate. They were assured of the option to withdraw from the study at any point, and the study’s anticipated outcomes were intentionally undisclosed. The protocol was approved

h before testing and maintained regular sleep and dietary routines while avoiding supplements and stimulants. The participants received full information about the study procedures, including potential risks, before providing written informed consent to participate. They were assured of the option to withdraw from the study at any point, and the study’s anticipated outcomes were intentionally undisclosed. The protocol was approved by the Bioethics Committee for Scientific Research (3/2021) at the Jerzy Kukuczka Academy of Physical Education and performed according to the ethical standards of the Declaration of Helsinki 2013. 2.3. Procedures 2.3.1. Experimental Session Testing was performed on an indoor certified synthetic track (Mondo S.p.A., Alba, Piedmont, Italy). All athletes used their spikes during sprinting tests and regular running shoes during jumping assessments. All of the athletes performed a sprint-specific warm-up that was consistent with the participants’ normal training routines. The individualized warm-up included jogging (5 min), dynamic stretching (targeting major muscle groups used in sprinting), skipping drills (three sets of 20 m), and progressive accelerations over 30–40 m (three repetitions). These elements aimed to ensure readiness for the sprinting and jumping tasks. Following the warm-up, the participants proceeded to perform the CMJ and 50 m sprint trials. 2.3.2. Measurement Tools Jumping performance was assessed using a force plate (ForceDecks, Vald Performance, Brisbane, Australia) with a sampling rate of 1000 Hz which had been previously validated

Appl. Sci.2025,15, 2125 4 of 11 for reliability and accuracy [22]. Sprinting time was measured using timing photocells (Microgate, Bolzano, Italy) positioned at 0, 5, 20, 30, 40, and 50 m. The OptoJump–Microgate optical measurement system (Microgate, Bolzano, Italy) was used to capture kinematic variables, specifically ground contact time and flight time during sprint steps. This system consists of interconnected rods equipped with optical sensors, positioned along the track’s length and width. 2.3.3. Activation Protocol The activation protocol included a unilateral resistance exercise in the form of the Bulgarian split squat with a load equal to 15% BM. The Bulgarian split squat targets the quadriceps, glutes, and hamstrings, activating significant muscles for sprinting. The split squat position was controlled in accordance with suggestions of Stastny et al. [7]. The isometric contraction during the split squat position lasted for 10 s. The load was applied through two dumbbells held in both hands. Following a 1 min rest interval, each athlete performed 10 vertical single-leg hops for each limb. The objective of the single-leg hops was to stimulate the SSC, thus performing them as quickly as possible. Two sets of each exercise for both limbs were performed with a 2 min rest interval between sets. 2.3.4. Experimental Procedures All athletes prepared for the testing using their individual pre-competition warm- up, which included jogging, dynamic stretching, skipping, progressive accelerations over 30–40 m, and several functional exercises to enhance specific sprinting movement patterns. At first, two CMJs with arm swing were performed on a force plate with a 1 min rest interval in between. The best performance was recorded for further analysis. Afterward, all athletes performed two 50 m all-out sprints from a crouched start with a 5 min rest interval between the trials. The best performance was recorded for further analysis. After several minutes of rest and the change of footwear from spikes to running shoes, the PAPE activation protocol was initiated. The activation protocol included two sets of isometric Bulgarian split squats followed by 10 single-leg vertical hops. The isometric split squat was performed with a load of 15% BM and lasted

The best performance was recorded for further analysis. After several minutes of rest and the change of footwear from spikes to running shoes, the PAPE activation protocol was initiated. The activation protocol included two sets of isometric Bulgarian split squats followed by 10 single-leg vertical hops. The isometric split squat was performed with a load of 15% BM and lasted for 10 s. Following an 8 min rest interval, the CMJ was repeated and, similarly to the baseline evaluations, the best performance was recorded. This rest interval time was chosen since the peak PAPE effect typically falls within this rest period [5]. After an additional 2–3 min of rest during which the athletes changed their footwear once again, the final two 50 m sprints were performed. 2.3.5. Countermovement Jump Performance Assessment Each athlete performed two attempts of the CMJ with an arm swing following the warm-up and an additional two attempts after the activation protocol [10,19]. Athletes settled into the countermovement position to a self-selected depth and immediately fol- lowed with a maximal effort vertical jump. The athletes were instructed to land in the same position as the take-off, in the midsection of the force plate. The jump height from take-off velocity and the modified reactive strength index (RSImod) were recorded. The best jump in terms of height was kept for further analysis. 2.3.6. Sprint Performance Assessment Sprint times were recorded with gates at 0, 5, 20, 30, 40, and 50 m. To prevent premature triggering by swinging limbs, the gates were set approximately 1 m above the ground, corresponding to the athletes’ hip height. Athletes initiated their sprints from a crouched position, placed 0.3 m behind the initial timing gate, ensuring a controlled start. Times were measured with precision to the nearest 0.001 s, and the fastest 50 m sprint time was selected for further analysis.

Appl. Sci.2025,15, 2125 5 of 11 2.4. Statistical Analysis All statistical analyses were performed using the JASP software (Version 0.18.3; macOS Sonoma 14.2.1; JASP Team, University of Amsterdam, Amsterdam, The Netherlands) and are shown as means with standard deviations (±SD) and 95% confidence intervals. Statistical significance was set top< 0.05. The normality of the data distribution was checked using Shapiro–Wilk tests. To investigate the effects of CA on CMJ and sprint performance, the Wilcoxon rank-sum test (for 40 m and 50 m sprint time and contact time due to violated data distribution) and paired samplet-tests were used. The magnitude of mean differences is expressed with standardized effect sizes. Thresholds for qualitative descriptors of Cohen’s d were interpreted as≤0.20 “small”, 0.21–0.79 “medium”, and >0.80 as “large”. 3. Results Thet-test showed a significant increase in CMJ height (56.3±8.1 cm [95%CI: 51.4 to 61.2 cm] vs. 57.7±7.6 cm [95%CI: 53.1 to 62.3 cm], 2.6±3.1%,p< 0.001; d = 0.89 [95%CI: 0.23 to 1.53]) (Figure).Appl. Sci. 2025, 15, 2125 5 of 11 ground, corresponding to the athletes’ hip height. Athletes initiated their sprints from a crouched position, placed 0.3 m behind the initial timing gate, ensuring a controlled start. Times were measured with precision to the nearest 0.001 s, and the fastest 50 m sprint time was selected for further analysis. 2.4. Statistical Analysis All statistical analyses were performed using the JASP software (Version 0.18.3; ma- cOS Sonoma 14.2.1; JASP Team, University of Amsterdam, Amsterdam, The Netherlands) and are shown as means with standard deviations (±SD) and 95% confidence intervals. Statistical significance was set to p < 0.05. The normality of the data distribution was checked using Shapiro–Wilk tests. To investigate the effects of CA on CMJ and sprint per- formance, the Wilcoxon rank-sum test (for 40 m and 50 m sprint time and contact time due to violated data distribution) and paired sample t-tests were used. The magnitude of mean di fferences is expressed with standardized effect sizes. Thresholds for qualitative descriptors of Cohen’s d were interpreted as ≤0.20 “small”, 0.21–0.79 “medium”, and >0.80 as “large”. 3. Results The t-test showed a significant increase

(for 40 m and 50 m sprint time and contact time due to violated data distribution) and paired sample t-tests were used. The magnitude of mean di fferences is expressed with standardized effect sizes. Thresholds for qualitative descriptors of Cohen’s d were interpreted as ≤0.20 “small”, 0.21–0.79 “medium”, and >0.80 as “large”. 3. Results The t-test showed a significant increase in CMJ height (56.3 ± 8.1 cm [95%CI: 51.4 to 61.2 cm] vs. 57.7 ± 7.6 cm [95%CI: 53.1 to 62.3 cm], 2.6 ± 3.1%, p < 0.001; d = 0.89 [95%CI: 0.23 to 1.53]) (Figure 1). Figure 1. Countermovement jump height before and after the conditioning activity. RSImod (0.8 ± 0.2 m/s [95%CI: 0.68 to 0.92 m/s] vs. 0.83 ± 0.17 m/s [95%CI: 0.72 to 0.93 m/s], 4.1 ± 7.5%, p = 0.038; d = 0.41 [95%CI: −0.16 to 0.97]) at post-CA compared to pre-CA is shown in Figure 2. Figure 1.Countermovement jump height before and after the conditioning activity. RSImod (0.8±0.2 m/s [95%CI: 0.68 to 0.92 m/s] vs. 0.83±0.17 m/s [95%CI: 0.72 to 0.93 m/s], 4.1±7.5%,p= 0.038; d = 0.41 [95%CI:−0.16 to 0.97]) at post-CA compared to pre-CA is shown in Figure.Appl. Sci. 2025, 15, 2125 6 of 11 Figure 2. Modified reactive strength index before and after the conditioning activity. T-tests showed a significant decrease in the 20 m sprint time (p = 0.006). However, they did not show any significant changes in the 50 m sprint time (p = 0.227), contact time (p = 0.644), and flight time (p = 0.421) (Table 1). Moreover, the Wilcoxon rank-sum test showed significant changes in the 40 m (p = 0.02) but not in the 50 m sprint time (p = 0.363). Table 1. Sprint performance before and after the conditioning activity. Pre‐CA (95% CI) Post‐CA (95% CI) d (95% CI) % 20 m sprint time [s] 2.975 ± 0.118 (3.047 to 2.904) 2.952 ± 0.117 (3.022 to 2.881) −0.2 (−0.966 to 0.575) −0.8 ± 0.9 40 m sprint time [s] 5.143 ± 0.215 (5.273 to 5.013) 5.12 ± 0.21 (5.245 to 4.992) −0.11 (−0878 to 0.661) −0.5 ±

the conditioning activity. Pre‐CA (95% CI) Post‐CA (95% CI) d (95% CI) % 20 m sprint time [s] 2.975 ± 0.118 (3.047 to 2.904) 2.952 ± 0.117 (3.022 to 2.881) −0.2 (−0.966 to 0.575) −0.8 ± 0.9 40 m sprint time [s] 5.143 ± 0.215 (5.273 to 5.013) 5.12 ± 0.21 (5.245 to 4.992) −0.11 (−0878 to 0.661) −0.5 ± 0.6 50 m sprint time [s] 6.242 ± 0.275 (6.408 to 6.076) 6.23 ± 0.27 (6.393 to 6.067) −0.04 (−0.813 to 0.725) −0.2 ± 0.5 Contact time [ms] 0.112 ± 0.005 (0.115 to 0.109) 0.112 ± 0.004 (0.114 to 0.109) 0 (−0.769 to 0.769) −0.1 ± 2.8 Flight time [ms] 0.120 ± 0.005 (0.123 to 0.116) 0.120 ± 0.006 (0.124 to 0.117) 0 (−0.769 to 0.769) 0.6 ± 1.9 CA—conditioning activity, CI—confidence interval. 4. Discussion The aim of this study was to assess the acute effects of combined isometric and plyometric unilateral CAs on subsequent CMJ and 50 m sprint performance (with split measures at 0–20 and 0–40 m) in sprinters. Considering the current state of knowledge, it seemed fully justified to evaluate possible changes in motor pattern changes and the role of the speed of CA in determining the significance of exercise selection to elicit PAPE. The main findings of this study are that the applied CA led to an acute improvement in the Figure 2.Modified reactive strength index before and after the conditioning activity.

Appl. Sci.2025,15, 2125 6 of 11 T-tests showed a significant decrease in the 20 m sprint time (p= 0.006). However, they did not show any significant changes in the 50 m sprint time (p= 0.227), contact time (p= 0.644), and flight time (p= 0.421) (Table). Moreover, the Wilcoxon rank-sum test showed significant changes in the 40 m (p= 0.02) but not in the 50 m sprint time (p= 0.363). Table 1.Sprint performance before and after the conditioning activity. Pre-CA (95%CI) Post-CA (95%CI) d (95%CI) % 20 m sprint time [s] 2.975±0.118 (3.047 to 2.904) 2.952±0.117 (3.022 to 2.881) −0.2 (−0.966 to 0.575) −0.8±0.9 40 m sprint time [s] 5.143±0.215 (5.273 to 5.013) 5.12±0.21 (5.245 to 4.992) −0.11 (−0878 to 0.661) −0.5±0.6 50 m sprint time [s] 6.242±0.275 (6.408 to 6.076) 6.23±0.27 (6.393 to 6.067) −0.04 (−0.813 to 0.725) −0.2±0.5 Contact time [ms] 0.112±0.005 (0.115 to 0.109) 0.112±0.004 (0.114 to 0.109) 0 (−0.769 to 0.769) −0.1±2.8 Flight time [ms] 0.120±0.005 (0.123 to 0.116) 0.120±0.006 (0.124 to 0.117) 0 (−0.769 to 0.769) 0.6±1.9 CA—conditioning activity, CI—confidence interval. 4. Discussion The aim of this study was to assess the acute effects of combined isometric and plyometric unilateral CAs on subsequent CMJ and 50 m sprint performance (with split measures at 0–20 and 0–40 m) in sprinters. Considering the current state of knowledge, it seemed fully justified to evaluate possible changes in motor pattern changes and the role of the speed of CA in determining the significance of exercise selection to elicit PAPE. The main findings of this study are that the applied CA led to an acute improvement in the following 20 m and 40 m sprint performance, with no significant impact on the 50 m sprint time. Contact time and flight time during the 50 m sprint did not change due to the PAPE intervention. Moreover, a significant increase in CMJ height and RSI due to the CA was observed. Considering the positive effects of various resistance exercise activation protocols on sprint performance, e.g., isometric, concentric, eccentric, and plyometric [10,11,23], the authors of this study aimed to evaluate the combined effects of

The study assesses the impact of conditioning activities on sprint and jump performance.