Isometric vs. Dynamic Squat Pre-Loading: Acute PAPE Responses

Official title

Acute Post-Activation Performance Responses to Isometric and Dynamic Squat Pre-Loading Protocols: A Randomized Crossover Trial

Overview

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.

Detailed description

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.

Interventions

• Other dynamic conraction
  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 proto
• Other isometric contraction
  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
• Other dynamic and EMS contraction
  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
• Other isometric and EMS conraction
  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
• Other ems contraction
  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. Stim

Primary outcome measures

• Countermovement Jump (CMJ) Height [Time frame: aseline and 4 minutes after each experimental condition]
• Countermovement Jump with Arm Swing (CMJWH) Height [Time frame: Baseline and 4 minutes after each experimental condition]
• Zig-Zag Agility Performance [Time frame: Baseline and 4 minutes after each experimental condition]
• Shooting Speed [Time frame: Baseline and 4 minutes after each experimental condition]

Secondary outcome measures (3)

• Rating of Perceived Exertion (RPE) [Time frame: Immediately after each experimental condition]
• Rating of Perceived Discomfort (RPD) [Time frame: Immediately after each experimental condition]
• Perceived Fatigue [Time frame: Immediately after each experimental condition]

Eligibility criteria

Inclusion criteria

• Being healthy
• Male volleyball athletes
• Willing to maintain the intervention for all sessions

Exclusion criteria

• Being under 18 years old
• Having a chronic disease
• Contraindications for exercise

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Crossover

Masking

Single blind

Primary purpose

Treatment

Study locations

Turkey (Türkiye) · 1 center

• Karabuk University — Karabük

Publications

• 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. PMID 40112871
• 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. PMID 39360986

Identifiers

NCT: NCT07696026 · UKarabuk-6

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗