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

Abstract

This study investigates 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 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.

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 [3,4,5]. 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 differences can determine competition outcomes, incorporating an effective CA immediately preceding competitive performance may be desirable.

Isometric muscle contractions are widely utilized in both research and training due to their effectiveness in eliciting PAPE. Common modifications in isometric CA involve adjusting 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, enhancing 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 effectively 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 performance [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 examined 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 transmission 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.

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: men 10.96 ± 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 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 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 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 followed 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.

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 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 performance, 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 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

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).

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.

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. 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.

). 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).

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 these resistance exercise modalities on sprint performance. To the best of our knowledge, only the study by Kalinowski et al. [24] has, so far, investigated the acute effects of combined isometric and plyometric CA (comparing CAs performed in a bilateral and a unilateral manner) on CMJ performance. The authors reported a significant increase in CMJ height (from 32.5 ± 4.9 cm to 34.7 ± 4.6 cm; +2.2 cm, ~7.7 ± 8.5%) and RSImod (0.33 ± 0.06 to 0.36 ± 0.06; +0.3 m/s; 12 ± 15%) 6 min after two sets of 6 s of maximal bilateral half-back squats, immediately followed by 10 repetitions of drop jumps. Conversely, the unilateral protocol, consisting of 3 s of maximal effort per leg during unilateral single-leg squats, followed by five drop jumps per leg, resulted in a non-significant improvement in CMJ height (from 33.2 ± 5.5 cm to 34.2 ± 5.5 cm; +1 cm, 3.1 ± 6%) and RSImod (0.34 ± 0.07 to 0.36 ± 0.08 m/s; +0.02 m/s, 4 ± 9%). The CMJ height improvements observed in the present study were of similar magnitude to those reported following unilateral CA in Kalinowski et al. [24]’s study. Specifically, the relative improvements in CMJ (~2.6%), RSImod (~4.1%), and 20 m sprint time (−0.8%) were statistically significant. An increase of 1.4 cm in CMJ height or a 23 ms reduction in the 20 m sprint time can yield meaningful competitive advantages for elite athletes, with these findings highlighting the relevance of even small enhancements in performance following combined isometric and plyometric CA. Notably, Kalinowski et al. [24] included female semi-professional volleyball players as participants. While the literature presents conflicting evidence regarding the influence of sex [25,26,27] on the magnitude of PAPE [24], factors such as training background and sport specificity [28] and relative strength [15,29] may significantly impact PAPE responses. The CA protocol utilized by Kalinowski et al. [24] differed from that applied in the present study. The current protocol consisted of two sets of 10 s of Bulgarian split squat holds with an external load of 15% body mass, followed by 10 vertical hops. It is plausible that the CA stimulus in this study was weaker compared to that employed by Kalinowski et al. [24]. However, despite this difference, the improvements observed were of a comparable magnitude. Similarly, studies evaluating exclusively isometric CAs have demonstrated that short-duration maximal or near-maximal isometric contractions can effectively enhance performance [10,12,19]. Notably, the magnitude of the improvements in CMJ performance reported in this study closely aligns with those of Vargas-Molina et al. [10], where a single set of 4 s of submaximal isometric back squat at 75% of one repetition maximum was sufficient to elicit a PAPE response. This aligns with our findings, with a significant increase in CMJ height of ~2.8%. Furthermore, these findings emphasize the importance of identifying the optimal CA dosage to maximize performance benefits while minimizing unnecessary fatigue accumulation. Although the observed improvements in athletic performance were modest, it is noteworthy that the participants were highly trained athletes for whom even small performance gains can be meaningful. These findings highlight the need for further research on combined isometric–plyometric CAs, as they demonstrate potential as a simple and effective training stimulus.

The activation exercises targeted the quadriceps and gluteal muscles, both of which play a crucial role in the start and acceleration phases of sprinting. As hypothesized, the greatest performance improvements were observed in the first 20 m of the sprint distance. The activation of these muscle groups also contributed to a significant improvement in CMJ performance [8]. Both higher RSI and CMJ height have been shown to be related to starting speed and acceleration [30,31]. Although there was a trend toward improved performance over longer distances (40 and 50 m), these changes were of low magnitude. Given that contact time and flight time remained unchanged following the CA, it is likely that only the force output of the lower limb extensors influenced acceleration and starting speed within the first 20 m. Isometric holds in key sprinting positions might increase ankle and knee stiffness, which is essential for effective force transmission to the ground [32]. However, while these exercises engage the primary muscles, they lack the dynamic explosiveness and reactivity necessary for sprint acceleration [11,33]. Conversely, plyometric exercises emphasize rapid, high-intensity movements that leverage the SSC, stimulating fast-twitch muscle fibers and closely replicating the explosive demands of sprinting. Zimmermann et al. [16] showed improvements in 30 m sprint times 2 and 4 min post CA and following three sets of five CMJs. Similarly, Kümmel et al. [13] demonstrated that performing 10 consecutive reactive hops led to an enhanced drop jump performance, suggesting that plyometric training influences the muscle–tendon unit behavior during SSC movements. Furthermore, plyometric exercises can elicit a stretch reflex response, increasing excitation potential transmittance via Ia afferents, thereby enhancing neuromuscular activation [21]. Given their distinct physiological effects, combining isometric and plyometric CAs may provide a unique stimulus, potentially enhancing sprint performance via the PAPE effect. However, it remains uncertain whether this specific combination of isometric and plyometric CA is more effective than other activation protocols, as no direct comparisons were performed in this study. To draw more definitive conclusions, future research should examine isolated isometric and plyometric protocols, as well as alternative sequences in which plyometric exercises precede the isometric ones. However, due to the structured schedule of the junior national team’s training camp, it was not feasible to implement additional CA protocols within this study.

Unilateral activation exercises, which engage one side of the body at a time, offer several benefits for sprinters. Exercises such as the Bulgarian split squat, lunges, or single leg glute bridges are particularly effective, as they closely replicate the movement patterns and demands of sprinting [34]. Unilateral exercises improve coordination and balance between the left and right sides of the body, reducing imbalances and enhancing movement efficiency. Moreover, unilateral resistance exercises significantly engage the core muscles, thereby increasing stability and improving sprinting form [35]. This may be particularly beneficial in compensating for variations in muscle activity during sprinting, as muscle activation differs between straight and curved running [36]. Additionally, exercises such as lunges and Bulgarian split squats develop lower limb strength and power, both of which are essential for explosive block starts and powerful strides during the acceleration phase of sprinting [37]. Unilateral exercises also enhance proprioception, particularly in the ankle, knee, and hip joints, improving neuromuscular coordination and movement efficiency. Training each side of the body individually can optimize muscle activation, leading to a greater sprinting performance. Perhaps the most significant advantage of unilateral resistance exercises is their direct transferability to sprinting, as they mimic the specific movement patterns involved, making strength gains more functional and sprint-specific [32].

Interpreting the results of this experiment requires consideration of its limitations. One of the primary limitations of this study is the absence of a control group. This design choice was dictated by logistical constraints and the elite status of the participants, who were engaged in intensive training schedules. Future studies should include a control group performing the same evaluation protocol without the CA to isolate the effects of CA from other factors, such as repetition or learning effects. Furthermore, the small sample size (n = 13) limits the interpretation of the statistical results, particularly for effect sizes below 0.76, as statistical power falls below 0.8. This limitation is acknowledged, and future studies will aim to include larger participant groups to enhance statistical robustness. Additionally, this study did not evaluate participants’ subjective perceptions of performance, motivation, or exertion, limiting the ability to account for potential placebo effects. Future studies should incorporate subjective assessments, such as the rate of perceived exertion scale, to better understand these factors. Finally, caution is warranted when generalizing these findings to different populations. The study was conducted on well-trained junior sprinters, and the observed effects may not necessarily apply to athletes of different performance levels, training backgrounds, or disciplines. Future research should explore the applicability of these results across a broader range of athletic populations.

5. Conclusions

In conclusion, we state that our hypothesis was partially confirmed, as the combined isometric and plyometric exercise protocol enhanced CMJ performance and led to minor performance enhancements during the acceleration phase of the sprint. However, the 50 m sprint performance did not show significant improvements due to this form of CA.