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This randomized crossover study compared the acute post-activation performance responses to isometric and dynamic squat-based preconditioning protocols performed with and without electromyostimulation (EMS). Participants completed five randomized experimental conditions: maximal voluntary isometric contraction (MVIC), dynamic contraction (DC), MVIC+EMS, DC+EMS, and EMS only (O-EMS). Baseline and post-intervention assessments included countermovement jump (CMJ), countermovement jump with arm swing (CMJWH), zig-zag agility, and shooting speed, with post-tests conducted after a 4-minute recovery period. Perceptual responses, including ratings of perceived exertion (RPE), perceived discomfort (RPD), and fatigue (VAS), were recorded immediately after each protocol. All sessions were conducted between 14:00 and 16:00 under standardized conditions, with protocol order randomized and participants instructed to avoid strenuous exercise and food intake before testing.
This study aimed to compare the acute post-activation performance responses to isometric and dynamic squat-based preconditioning protocols, with and without EMS. All testing sessions were conducted between 14:00 and 16:00 to minimize the potential effects of circadian rhythms and fatigue on performance. The study was conducted using a randomized, crossover design. On the remaining five experimental days, the order of the protocols was randomized for each participant using a computer-generated randomization sequence (randomizer.org) to reduce order effects. During the first session, participants' anthropometric measurements were recorded, their one-repetition maximum (1RM) back squat loads were determined, and they were familiarized with the equipment and testing procedures. Participants completed five separate experimental sessions consisting of the following conditions: [A] Isometric Contraction + EMS (MVIC-EMS), [B] Dynamic Contraction + EMS (DC-EMS), [C] Dynamic Contraction (DC), [D] Isometric Contraction (MVIC), and [E] Only EMS (O-EMS). Before each experimental protocol, baseline measurements were obtained using countermovement jump (CMJ), CMJ with hands (CMJWH), zig-zag agility test, and shooting speed assessments. After each protocol, all tests were repeated after a 4-minute rest period (Chen et al., 2023). Under all conditions, the electrodes were placed identically by the same experienced researcher. Subsequently, players' shooting speeds were measured using a radar gun, with two trials performed and the highest value recorded. Immediately after each experimental protocol, ratings of perceived exertion (RPE), perceived discomfort (RPD), and perceived fatigue level were assessed using a visual analog scale (VAS) and recorded. Participants were instructed to refrain from food intake for 1.5 hours before testing, to avoid resistance training throughout the study period, and were verbally encouraged during all testing sessions.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Condition 1 | Experimental | Dynamic contraction |
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| Condition 2 | Experimental | isometric contraction |
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| Condition 3 | Experimental | Dynamic + EMS contraction |
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| Condition 4 | Experimental | Isometric + EMS Contraction |
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| Condition 5 | Experimental | EMS contraction |
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| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| dynamic conraction | Other | Participants performed a dynamic back squat conditioning protocol on a Smith machine consisting of five sets of one repetition at 90% of one-repetition maximum (1RM), with 1 min of passive recovery between sets. Each repetition included a controlled descent to approximately 90° of knee flexion, an explosive concentric phase, a 2-s isometric hold at full knee extension, and a slow, controlled eccentric phase (Pincivero et al.). All repetitions were supervised to ensure proper technique. The protocol was selected based on previous evidence supporting high-intensity resistance exercise as an effective conditioning activity for inducing PAPE responses (Dobbs et al.). |
| Measure | Description | Time Frame |
|---|---|---|
| Countermovement Jump (CMJ) Height | Change in countermovement jump (CMJ) height (cm) from baseline to 4 minutes after each conditioning protocol, measured using a jump assessment system. | aseline and 4 minutes after each experimental condition |
| Countermovement Jump with Arm Swing (CMJWH) Height | Change in countermovement jump with arm swing (CMJWH) height (cm) from baseline to 4 minutes after each conditioning protocol. | Baseline and 4 minutes after each experimental condition |
| Zig-Zag Agility Performance | Change in zig-zag agility performance time (s) from baseline to 4 minutes after each conditioning protocol. | Baseline and 4 minutes after each experimental condition |
| Shooting Speed | Change in maximal shooting speed (km/h) from baseline to 4 minutes after each conditioning protocol, measured using a radar gun. | Baseline and 4 minutes after each experimental condition |
| Measure | Description | Time Frame |
|---|---|---|
| Rating of Perceived Exertion (RPE) | Rating of perceived exertion assessed immediately after each conditioning protocol using the Borg CR-10 scale. | Immediately after each experimental condition |
| Rating of Perceived Discomfort (RPD) |
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Inclusion Criteria:
Exclusion Criteria:
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| Name | Role | Phone | Extension | |
|---|---|---|---|---|
| Neslihan Akçay, Doctorate | Contact | +905468426671 | neslihanozcan@karabuk.edu.tr | |
| Neslihan Akçay, Doctorate | Contact |
| Name | Affiliation | Role |
|---|---|---|
| Neslihan Akçay, Doctorate | Karabuk University | Study Chair |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| Karabuk University | Karabük | Turkey | 78200 | Turkey (Türkiye) |
| PubMed Identifier | Type | Citation | Retractions |
|---|---|---|---|
| 40112871 | Result | Sofuoglu C, Fujita RA, Keskin K, Kamis O, Akcay N. Acute electrical muscle stimulation effects on strength and anaerobic power in soccer players. Int J Sports Med. 2025 Jun;46(7):501-509. doi: 10.1055/a-2563-9289. Epub 2025 Mar 20. | |
| 39360986 | Result | Keskin K, Akcay N, Ozmen T, Contarli N, Yildiz KC, Sofuoglu C, Kamis O, Rolnick N, de Queiros VS, Montoye A. Effects of different pre-exercise strategies on jumping performance in female volleyball players. J Sports Med Phys Fitness. 2025 Jan;65(1):59-68. doi: 10.23736/S0022-4707.24.16196-8. Epub 2024 Oct 3. |
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| ID | Term |
|---|---|
| D007537 | Isometric Contraction |
| ID | Term |
|---|---|
| D009119 | Muscle Contraction |
| D009142 | Musculoskeletal Physiological Phenomena |
| D055687 | Musculoskeletal and Neural Physiological Phenomena |
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Triple (Participant, Care Provider, Outcomes Assessor) Participants were strictly separated and think their intervention is the main intervention. The same is true for care providers. Outcome assessors were unaware of participant group status and were not allowed to ask correspondingly
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| isometric contraction | Other | The isometric contraction protocol was conducted as described by Koźlenia and Domaradzki (2023) and Lim and Kong (2013). Participants assumed a squat position in a squat rack with the barbell fixed in place and the knee joint positioned at approximately 90° of flexion (Profitness 1030, Türkiye). The barbell was secured to the rack using safety pins, and participants were instructed to exert maximal force against the immovable bar to produce a MVIC. Each contraction lasted 3 seconds, and a total of 3 repetitions were performed with 2 min of rest between repetitions (Koźlenia & Domaradzki, 2023; Lim & Kong, 2013). |
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| dynamic and EMS contraction | Other | Participants performed a dynamic back squat conditioning protocol on a Smith machine consisting of five sets of one repetition at 90% of one-repetition maximum (1RM), with 1 min of passive recovery between sets. In the DC-EMS condition, electromyostimulation (EMS) was applied simultaneously throughout the conditioning protocol. Each repetition included a controlled descent to approximately 90° of knee flexion, an explosive concentric phase, a 2-s isometric hold at full knee extension, and a slow, controlled eccentric phase (Pincivero et al.). All repetitions were supervised to ensure proper technique. The protocol was selected based on previous evidence supporting high-intensity resistance exercise as an effective conditioning activity for inducing PAPE responses (Dobbs et al.). |
|
| isometric and EMS conraction | Other | The isometric contraction protocol was conducted as described by Koźlenia and Domaradzki (2023) and Lim and Kong (2013). Participants assumed a squat position in a squat rack with the barbell fixed in place and the knee joint positioned at approximately 90° of flexion (Profitness 1030, Türkiye). The barbell was secured to the rack using safety pins, and participants were instructed to exert maximal force against the immovable bar to produce an MVIC. Each contraction lasted 3 seconds, and a total of three repetitions were performed with 2 min of rest between repetitions (Koźlenia & Domaradzki, 2023; Lim & Kong, 2013). In the MVIC-EMS condition, electromyostimulation (EMS) was applied simultaneously during each maximal voluntary isometric contraction. |
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| ems contraction | Other | EMS was delivered bilaterally to the quadriceps using a portable stimulator (Compex Rehab 400, Compex Medical SA, Switzerland) with a biphasic symmetrical rectangular waveform (75 Hz, 450 μs). Four self-adhesive electrodes were placed over the vastus medialis and vastus lateralis muscles of both legs. Participants remained seated for 10 min with the knees flexed at approximately 90° and the hips flexed at approximately 110°, while receiving EMS without performing any voluntary contractions. Stimulation intensity was gradually increased to the highest level tolerated by each participant and maintained throughout the intervention (Paillard et al., 2008; Sofuoğlu et al., 2025). |
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Rating of perceived discomfort assessed immediately after each conditioning protocol using the Borg CR-10 scale.
| Immediately after each experimental condition |
| Perceived Fatigue | Perceived fatigue assessed immediately after each conditioning protocol using a visual analog scale (VAS). | Immediately after each experimental condition |