Acute Effects of High-intensity Interval Aerobic and Functional Training at Different Intensities

Official title

Evaluation of the Acute Effects of High-intensity Interval Aerobic Training, Moderate- and High-intensity Functional Training, and Moderate-intensity Functional Training

Overview

Moderate-intensity physical exercise is widely recognized for its health benefits, yet time constraints limit adherence. High-intensity interval training (HIIT) has gained popularity as a more time-efficient alternative, eliciting significant cardiovascular, respiratory, metabolic, and neuromuscular responses. More recently, functional strength exercises have been integrated into high-intensity training, leading to high-intensity functional training (HIFT) and moderate-intensity functional training (MIFT). However, the acute physiological responses to these modalities remain underexplored compared to traditional HIIT (running or cycling) and strength training. This study aims to assess and compare the acute cardiovascular, metabolic, and neuromuscular responses of HIFT, MIFT, HIIT, and traditional strength training in healthy, physically active adults to inform their potential application in special populations.

Detailed description

Moderate-intensity physical exercise has long been a cornerstone in promoting health and well-being. However, despite its well-documented benefits, an exclusive focus on this training modality may overlook some important limitations. One such limitation is the challenge of dedicating sufficient time to physical activity to achieve health and fitness goals. Given this constraint, recent years have witnessed a significant shift in training modalities, moving away from continuous moderate-intensity exercise approaches \[e.g., 55-70% of peak heart rate (HRpeak) or 40-60% of maximal oxygen uptake (VO₂max)\] toward higher-intensity interval training protocols (e.g., \>90% HRpeak or \>85% VO₂max), thereby enhancing time efficiency and enjoyment for practitioners.

In this context, the most common type of training is high-intensity interval training (HIIT). HIIT consists of performing brief, high-intensity cyclic and continuous efforts (e.g., running or cycling) separated by predefined rest periods while using a single exercise modality. These short efforts (e.g., 1 to 4 minutes) at high intensity, whether cycling or running, elicit substantial cardiovascular, respiratory, metabolic, and neuromuscular stimuli, which can persist for hours after the workout.

Recently, this training approach has incorporated functional strength exercises-movements that mimic natural movement patterns and have practical applications in daily life-performed at high intensity \[e.g., \>75% of one-repetition maximum (1RM)\] and following a circuit-based exercise organization (i.e., performing one exercise after another rather than using simple sets and pauses), a modality commonly referred to as high-intensity functional training (HIFT). Reducing the intensity of prescribed functional exercises (e.g., 60% 1RM) brings the training program closer to the demands of daily activities, a modality commonly known as moderate-intensity functional training (MIFT). However, both HIFT and MIFT define their intensity theoretically, based on the relative intensity concerning the maximum dynamic concentric strength that individuals can develop in each exercise (%1RM). Meanwhile, the cardiovascular, respiratory, metabolic, and neuromuscular demands of these methodologies remain largely unexplored compared to running-based HIIT (HIIT-R), cycling-based HIIT (HIIT-C), and traditional strength training with moderate (M-FT) and high (H-FT) loads in healthy, physically active adults. Therefore, before these methods can be applied to special populations (e.g., individuals with chronic cardiovascular or respiratory diseases, cancer, or older adults), it is essential to first understand their acute response in healthy, physically active individuals.

Interventions

• Other High-intensity interval training, running
  Six sets of 2-minute runs will be performed at an intensity of 90-95% of the maximal aerobic speed (MAS) on a treadmill. The recovery between each set will be 2 minutes, during which the subject will walk at an intensity of 50-60% of MAS.
• Other High-intensity interval training, cycling
  Six sets of 2-minute cycling will be performed at an intensity of 90-95% of the maximal heart rate on a stationary bike. The recovery between each set will be 2 minutes, during which the subject will cycle at an intensity of 50-60% of maximal heart rate.
• Other High-intensity functional training
  Three sets of six repetitions will be performed at 80% of the one repetition-maximum (1-RM) for six exercises. The recovery between exercises will be the minimum time required to switch from one exercise to the next, and between sets, it will be two minutes. Participants will be instructed to move the load as quickly as possible during each repetition.
• Other Moderate-intensity functional training
  Three sets of six repetitions will be performed at 60% of the 1-RM for six exercises. The recovery between exercises will be the minimum time required to switch from one exercise to the next, and between sets, it will be two minutes. Participants will be instructed to move the load as quickly as possible during each repetition.
• Other Moderate intensity traditional strength training
  Three sets of six repetitions will be performed at 60% of the 1-RM for six exercises. The recovery after each set will be two minutes of passive rest. Participants will be instructed to move the load as quickly as possible during each repetition.
• Other High intensity traditional strength training
  Three sets of six repetitions will be performed at 80% of the 1-RM for six exercises. The recovery after each set will be two minutes of passive rest. Participants will be instructed to move the load as quickly as possible during each repetition.

Primary outcome measures

• Heart rate variability [Time frame: Week 0 (baseline), Weeks 1-4 (during intervention and 24, 48, and 72 hours post-intervention)]

Secondary outcome measures (6)

• Post-exercise oxygen debt [Time frame: Weeks 2-4 (after every intervention session)]
• Delayed onset muscle soreness [Time frame: Weeks 2-4 (24, 48, and 72 hours post-intervention)]
• Satisfaction with the type of training [Time frame: Weeks 2-4 (right after every intervention session and 24 hours post-intervention)]
• Subjective post-exercise fatigue [Time frame: Weeks 2-4 (right after every intervention session and 24 hours post-intervention)]
• Perceived effort [Time frame: Weeks 2-4 (right after every intervention session and 24, 48, and 72 hours post-intervention)]
• Gas exchange analysis [Time frame: Weeks 2-4 (during intervention sessions)]

Eligibility criteria

Inclusion criteria

• Be 18 years of age or older.
• Have at least 6 months of experience in strength training with intensities greater than 75% of one maximum repetition (1-RM).
• Be classified as active according to the International Physical Activity Questionnaire (IPAQ) score.

Exclusion criteria

• Musculoskeletal injury within the 6 months prior to the first visit to the laboratory.
• Recent major surgery (<3 months).
• Having a medical condition in which physical activity is contraindicated (assessed with the Physical Activity Readiness Questionnaire, PAR-Q+).

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

Other

Study locations

Spain · 1 center

• Miguel de Cervantes European University — Valladolid

Identifiers

NCT: NCT07180550 · PI-DOC008-HIIT-HIFT-FT

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗