Event-Specific Adaptations to CrossFit and Running-Based HIIT in Elite Distance Runners at Moderate Altitude

Summary

The goal of this clinical trial is to compare the effects of two high-intensity training programs on physical performance and physiological adaptations in elite male middle- and long-distance runners aged 25 to 35 years who live and train at moderate altitude (approximately 1,400 meters above sea level).

The main questions it aims to answer are:

Does running-based high-intensity interval training improve aerobic fitness and race performance in elite distance runners? Does CrossFit training improve muscle strength, power, and physiological markers in elite distance runners? Researchers will compare running-based high-intensity interval training (HIIT) with CrossFit training to determine how each program affects aerobic capacity, strength, running performance, and selected blood markers.

Participants will:

Be randomly assigned to either a running-based HIIT program or a CrossFit training program Train five days per week for six weeks under supervision Complete exercise testing before and after the training period, including treadmill fitness testing and timed running trials Provide blood samples before and after the intervention to measure selected physiological markers

Conditions

• Athletic Performance
• Physical Endurance
• Altitude Training Adaptation
• Aerobic Capacity
• Neuromuscular Performance
• Exercise-Induced Inflammation
• Adaptation Reaction

Interventions

BEHAVIORAL

Running-Based High-Intensity Interval Training (HIIT)

Participants performed five supervised HIIT sessions per week for six weeks at moderate altitude (approximately 1,400 m) in Zahedan, Iran. Each session lasted 60-75 minutes and was conducted on a standard 400-m synthetic track. Sessions consisted of 4-6 intervals of 2-4 minutes duration performed at 90-95% of maximum heart rate (HRmax), interspersed with 2-3 minutes of active recovery at approximately 50% HRmax. Participants self-selected their interval pace to maintain heart rate within the prescribed target zone throughout each work bout. Exercise intensity was continuously monitored using Polar H10 chest-strap heart rate sensors. Progressive overload was applied throughout the intervention period.

BEHAVIORAL

CrossFit-Based High-Intensity Training (CF)

Participants performed five supervised CrossFit sessions per week for six weeks at moderate altitude (approximately 1,400 m) in Zahedan, Iran. Each session lasted 60-75 minutes and followed a structured four-part format: (i) Dynamic warm-up incorporating mobility exercises and movement preparation (10-15 minutes); (ii) Strength and skill work targeting foundational lifting patterns and gymnastic movements (15-20 minutes); (iii) High-intensity Workout of the Day (WOD) at 85-95% HRmax (10-20 minutes); (iv) Cool-down consisting of static stretching and controlled breathing exercises (5-10 minutes). WODs were selected from the official CrossFit programming archive (2021-2023) and individually scaled by a Level 2 CrossFit-certified coach. Loading for barbell movements was prescribed at 30-85% of baseline 1RM values. Bodyweight and kettlebell movements were regulated by repetition targets and RPE scores of 14-18 on the Borg 6-20 scale. Progressive overload was applied biweekly through increa

Sponsors & Collaborators

• University of Sistan and Baluchestan

  lead OTHER

Principal Investigators

• Mohammadreza Rezaeipour · University of Sistan and Baluchestan

Study Design

Allocation

RANDOMIZED

Purpose

BASIC_SCIENCE

Masking

SINGLE

Model

FACTORIAL

Eligibility

Min Age

25 Years

Max Age

35 Years

Sex

MALE

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2021-09-01

Primary Completion

2021-10-15

Completion

2021-10-30

Countries

• Iran

Study Locations