This study aims to compare the effects of three different training intensity distribution (TID) models-polarized, threshold, and pyramidal-on physiological and performance adaptations in recreational distance runners. Twenty-four participants will be assigned to one of the three training interventions and will complete an 8-week structured running program based on the respective TID approach.

The primary objective is to determine whether different TID models elicit distinct changes in key physiological markers and endurance performance. The study seeks to answer whether a specific intensity distribution strategy provides superior adaptations in recreational runners when training is prescribed over a controlled intervention period.

This study adopts a parallel-group experimental design to compare the effects of three training intensity distribution (TID) models-polarized, threshold, and pyramidal-on physiological and performance adaptations in recreational distance runners.

Eligible participants are required to be recreational runners with a minimum training frequency of four sessions per week. Following enrollment, all participants complete a one-week pre-intervention phase dedicated to baseline assessments and familiarization with testing procedures.

During this phase, participants will performe a comprehensive physiological evaluation to determine key endurance-related variables. These include ventilatory thresholds (e.g., VT1 and VT2), running economy, and maximal oxygen uptake (VO₂max), assessed through an incremental exercise test under standardized laboratory conditions. In addition, participants perform a 5-km time trial on a standardized course or controlled conditions to assess endurance performance.

Based on the physiological assessment, individual training intensities are prescribed using a five-zone intensity model derived from ventilatory thresholds and maximal aerobic capacity. This approach allows for precise classification of training load and ensures consistency in the application of the three TID models across participants.

Following baseline testing, participants are allocated to one of the three intervention groups (polarized, threshold, or pyramidal) and complete an 8-week structured endurance training program. Each training model differs in the relative distribution of time spent across the five intensity zones, while overall training frequency and general structure are maintained comparable between groups.

Training sessions are monitored using participants' GPS-enabled sport watches, which record variables such as duration, distance, pace, and heart rate. These data are used to quantify training load and verify adherence to the prescribed intensity distribution. Participants are instructed to follow the assigned training program and upload their training data regularly for supervision and compliance tracking.

At the end of the 8-week intervention, all baseline assessments are repeated under the same conditions. This includes the physiological testing to reassess ventilatory thresholds, running economy, and VO₂max, as well as the 5-km time trial to evaluate changes in endurance performance.

The primary aim of the study is to examine whether different TID models induce distinct adaptations in physiological determinants and performance outcomes when applied in a controlled, prospective training intervention in recreational runners.

Inclusion Criteria:

• age ≥ 18 years;
• a habitual training frequency of ≥ 4 sessions·week
• running experience ≥ 2 years;
• absence of musculoskeletal injuries in the preceding 3 months

Exclusion Criteria:

• an official 10-km race time > 40:00 min:s for men and > 50:00 min:s for women
• any cardiometabolic disease