Effects of Interval and Power Training on the Physical, Physiological, and Training Characteristics of Trained Distance Runners

The running performance of middle- and long-distance runners is influenced by factors, such as maximal oxygen uptake (V̇O_2Max), velocity at V̇O_2Max (vV̇O_2Max), maximum metabolic steady state (MMSS), running economy (RE), and sprint capacity (1). While performance adaptations depend on training characteristics, both high-intensity interval training (HIIT) and resistance training (RT) models offer viable alternatives for training periodization (2).

Training for endurance runners aims to improve both performance and its physiological determinants, which appear to influence performance in highly trained or elite runners competing in events ranging from 1500 m to the marathon (3). The training process emphasizes several key aspects, including periodization, training methods and monitoring, performance prediction, running technique, and the prevention and management of injuries related to endurance running (4).

Interval training involves alternating between short bursts of intense exercise and periods of lower-intensity activity or complete rest for recovery (5). High-intensity interval training is an extension of IT (6), enhancing an athlete's cardiorespiratory and metabolic functions, improving both aerobic and anaerobic capacities, and ultimately leading to better physical performance (7).

There is limited research on how coaches of well-trained middle- to long-distance runners apply IT methods. While research tends to emphasize physiological outcomes, coaches prioritize performance, creating a gap between the IT techniques studied in research and those used in practice (8).

Interval and combined training are more effective strategies than continuous training for improving athlete performance (9). In contrast, a framework for integrating strength training (ST) with traditional sport-specific training can enhance middle- and long-distance performance by reducing the energy cost of locomotion and increasing maximal power and strength (10).

Power training, which combines plyometric and resistance exercises, can benefit recreational, young male, and well-trained distance runners (11). This type of training can improve their explosive strength, neuromuscular function, RE, and endurance performance across various training intensity targets (12).

Plyometric training, an extension of power training, enhances pre-adolescent boys' muscle thickness, stride angle, fascicle length, tendon stiffness, jumping ability, lower body strength, and stretch-shortening cycle (SSC) (13). Heavy RT, compared to plyometric training, improves distance runners' knee and ankle strength, leg acceleration, propulsion, biomechanical and neuromuscular changes, RE, and TT performance (14).

Explosive plyometric and high-intensity RT, which combine concurrent strength and endurance training (SET), lack explicit discussion (15). The impact of ST on work economy, V̇O_2Max/V̇O₂peak, general strength, and running performance has typically been studied across a wide range of trained and well-trained individuals, including those of varying age, sex, experience, and disciplines, particularly in middle- and long-distance runners (16).

The effects of ST on physical, physiological, and training-related factors, especially in 800 m to 1500 m runners, have been explicitly examined in previous studies (16-20). However, the combined effects of interval and power training on participants of different ages, genders, training backgrounds, events, and control conditions, particularly in middle- and long-distance running ranging from 800 m to 10000 m, remain unclear (21-24).

The combined effects of interval and power training interventions, compared to a control group, do not consistently show superior improvements in all physical, physiological, and training characteristics.

1.1. Theoretical and Conceptual Framework

The experimental design shown in Figure 1 was adapted from a previous source (1, 24) and has been modified.

Figure 1.

Experimental study methodological flow chart

One of the objectives of this study was to investigate the combined effects of customized interval and power training interventions compared to a control group over an extended period.

The primary objective was to compare the combined effects of interval and power training with a control group. Our key findings revealed significant improvements in strength endurance, speed endurance, and RE. Based on these key findings, the first null hypothesis was largely refuted in most physical (demographic and anthropometric) characteristics, as detailed in Table 2. The results from both descriptive statistics (Appendix 1 in Supplementary File) and inferential statistics, including paired sample t-tests, ANOVA, and multiple mean comparisons using Bonferroni correction (Appendix 1 in Supplementary File), support this conclusion.

The second null hypothesis was rejected, as there were consistent improvements in most physiological characteristics related to RE. Notable improvements were observed in the following: Four hundred m sprint performance (108.83, P = 0.000), 1.5 km Kosmin speed endurance (38.39, P = 0.000), 3 km maximum speed TT (9.29, P = 0.000), maximum exercise heart rate (bpm) (23.40, P = 0.000) (Figure 2), LS (sec) (46.56, P = 0.000), and Sprint Bounding Index (SBI) (sec) (45.66, P = 0.000) (Figure 3). These results align with previous research, which indicates that interventions involving strength, interval, and combined training improve distance running performance (33, 35).

Figure 2.

Post-test (POT) results of maximum exercise heart rate

Figure 3.

Post-test (POT) results of Sprint Bounding Index (SBI)

Conversely, some variables demonstrated a decrease in performance, including BalkeV̇O_2Max (50.99, P = 0.000), leg press (38.42, P = 0.000), and squat (46.74, P = 0.000). This is supported by the pre- and post-test scores presented in Table 3, which show statistically significant differences in all performance metrics after the 32-week power intervention.

The third null hypothesis was accepted, as most test variables related to training characteristics were not statistically significant, and small effect sizes were observed. From the third subgroup analysis, only sleep habits showed a statistically significant change (0.04, 3.43). Overall, the cumulative effects of our key findings across all three hypotheses indicate statistically significant changes (P < 0.05) with a large effect size (η² > 0.14) (Table 4).

The primary aim of this study was to investigate the combined effects of interval and power training compared to the control group in POT results. Our main findings demonstrated significant improvements in participants' strength endurance, speed endurance, and RE, from both physical and physiological fitness perspectives.

To clarify our discussion, significant changes were observed in physical characteristics related to chronological age, BMI, fat-free mass, and maximum thigh circumference. These changes encompass both demographic factors (such as age, sex, culture, and cultural influences) and anthropometric factors (such as body type, structure, and genetic composition). However, no significant changes were noted in certain physical characteristics, such as sex, fields of study, and weight.

Similar to our findings, elite Ethiopian female runners exhibit an ideal combination of height, weight, and BMI. They have lower body weight and fat mass, with an increased lean muscle mass relative to their total body mass, which suggests an ectomorphic body type—an essential characteristic for running success (23, 33).

A separate study revealed that participants from East African countries, including Kenya and Ethiopia, make up less than 0.1% of the global population but consistently record the fastest race times. These runners are younger than their non-African counterparts (36).

In the 1960s, the Kalenjin ethnic group in Kenya and the Oromo ethnic group in Ethiopia emerged as dominant forces in long-distance running, often linked to a combination of genetic and cultural factors. Genetic studies have revealed variations in genes associated with body structure, circulatory and respiratory systems, energy metabolism, and calcium regulation. These genetic traits play a significant role in their running abilities (37).

After 32 weeks of combined interval and power training, significant improvements were observed in physiological characteristics, including LS (strength and speed endurance) and RE (speed and endurance) tests across all performance metrics, compared to the control groups.

These significant improvements were seen in 400 m sprint performance, 1.5 km Kosmin speed endurance, 3 km maximum speed TTs, LS, SBI (power and speed), and maximum exercise heart rate, all of which showed a large effect size (η² > 0.14).

Furthermore, our key findings indicate that middle-distance runners (0.8 - 3 km) and long-distance runners (5 - 42.2 km) from Kenya and Ethiopia demonstrate exceptional RE and excel in competitions at both national and international levels. Elite female long-distance runners from East Africa, such as Ethiopians and Kenyans, have shown remarkable endurance performance in the 12-minute Cooper test. Additionally, elite Black East African endurance runners from Eritrea, recognized as top athletes, display superior aerobic capacity and RE.

Anaerobic speed qualities benefit from ST, which has been shown to improve RE or TT performance by 2 - 8% over distances of 1.5 to 10 km. Various training factors—including intensity distribution, periodization, training volume, competition distance and frequency, training surface, footwear, running season, and topography—play a role in these improvements (7, 10, 13, 14, 16, 33, 38).

Interval training serves as a key indicator of fatigue recovery time and neuromuscular adaptations, such as peak torque (PT) and rate of torque development (RTD), which are measured after two sprints in a 5 × (2 × 30 m) repeated sprint protocol, as well as in knee flexor muscles (39-43).

Power training, which includes plyometric and strength exercises, maximizes type 1 muscle fibers and delays the activation of less efficient type 2 fibers during multi-joint, closed-chain high-load exercises such as the back squat. This training method enhances force and peak power output in elite middle- and long-distance runners. It improves speed development, boosts speed-related fitness, 3 km performance times, RE, muscle power, neuromuscular adaptations, and the dose-response relationship (24, 37).

Incorporating interval and ST into the weekly routine of Black East African female runners from Kenya and Ethiopia enhances both RE and performance. High-intensity IT improves aerobic fitness, muscular endurance, O_2Max, strength, power, lean body composition, sprint speed, and RE TT performance among middle- and long-distance runners (6, 7, 11, 12, 15, 16).

Heavy resistance and strength training (HRST) are more effective than SET in increasing maximal strength, muscle power, anaerobic capacity, and sport-specific endurance. Short-term plyometric training produces comparable results across various sports and environmental conditions, whether at sea level or high altitude (39-41).

Optimizing biomechanical factors, favorable weather conditions, and running speed to improve running efficiency involves reducing the metabolic cost of running. Key factors such as ground contact time (GCT), stride length, stride frequency, joint angles, and foot strike patterns significantly affect running efficiency. Strategies like drafting, taking advantage of tailwinds, running downhill, and making footwear modifications can enhance performance. Efficient conversion of oxidative energy and the fractional utilization of V̇O_2Max are critical for distance running success (39-41).

A 40-week strength-training program improves maximal and reactive strength, RE, and vV̇O_2Max in competitive distance runners, without causing concurrent hypertrophy (42). Continuous interval aerobic training followed by ST significantly increases V̇O_2Max and RE (43).

Resistance and plyometric exercises, when performed at low to high intensity, are an effective strategy for improving RE in highly trained middle- and long-distance runners. These workouts are recommended 2 - 3 times per week for a duration of 8 - 12 weeks. A meta-analysis on ST found a significant increase in elite runners' RE, with a standardized mean difference of 21.42 (95% confidence interval: 22.23 to 20.60) (44, 45).

However, in all three groups, certain physiological parameters, such as BalkeV̇O_2Max (general endurance and speed endurance), leg press, and squat POTs, showed a significant decrease. Table 3 reveals discrepancies in the physiological parameters of Kenyan and Ethiopian middle- (0.8 - 3 km) and long-distance (5 - 42.2 km) runners, who demonstrate higher V̇O_2Max levels, ranging from 72.6 to 81.9 ml/kg/min.

A comparison between Eritrean and Spanish runners showed similar V̇O_2Max results (73.8 ± 5.6 mL/kg/min vs. 77.8 ± 5.7 mL/kg/min), with the upper limit of aerobic metabolism being higher for Eritrean runners. This performance is influenced by factors such as V̇O_2Max, sustainable fractional utilization of V̇O_2Max, lactate threshold (LT), blood lactate levels, and body composition, all shaped by neurobiological traits that promote habitual aerobic exercise (10, 16-18, 21, 46, 47).

In recent years, the combined effect of interval and power training methods has increasingly improved V̇O_2Max, lowered resting heart rates, reduced blood pressure, and decreased fractional utilization at O_2Max. Velocity at anaerobic threshold (vAT) has been shown to improve V̇O_2Max, RE, and running speed in middle- and long-distance athletes (4-9, 11, 12, 15, 16).

In the majority of physiological characteristics, after the 32-week intervention, statistically significant changes and large effect sizes were observed in the experimental groups compared to the control group. The present study, when compared to previous studies in terms of training modalities, intervention period, P < 0.05, η² > 0.14, and the references indicated in Table 5, shows similar findings.

Regarding the third training characteristic, except for sleep habits, the subgroup analysis of POT results showed a significant decrease after 32 weeks of observation (P > 0.05), but with a small effect size (η² < 0.01). Training-related factors, including living and training altitude, training habits (e.g., stretching, IT, power training, technique training), training experience, training volume, number of training sessions, recovery practices (e.g., rest, massage), running surface, footwear, and nutritional intake, all significantly increased.

In contrast to our findings, a small effect size favored fast training over low (moderate) intensities (defined as 60 - 79% of one-repetition maximum), with an effect size of 0.31 and a P-value of 0.06. Furthermore, strength gains between the conditions were not influenced by training or chronological age (2, 49, 50).

The observed training log of each runner's typical regimen over the past eight months considered altitude training, commonly practiced by elite endurance athletes at elevations between 1600 and 2400 meters. This approach introduces unique environmental stressors that enhance running performance in both altitude and sea-level competitions. Advances in nutrition and physiological interventions at elevations above 3000 meters, including the use of nutritional supplements, optimize adaptations to hypoxic conditions (39-41).

High-altitude living, rigorous training, low BMI, and low body fat all enhance endurance performance. However, nutritional strategies aimed at fat oxidation and weight loss may have unintended consequences. Instead, marathon training should provide adequate dietary energy, essential macronutrients, and important micronutrients like iron to support long-distance running success (40, 49, 50).

Optimal nutrition is crucial for competitive athletes, and endurance performance can be improved with carbohydrate-rich diets, proper hydration, glycogen storage, and carbohydrate and fluid intake during races. Factors such as unique dietary practices and specific anthropometric traits contribute to the dominance of East African distance runners (51).

Advanced footwear technology has enhanced endurance performance in distance running. Female runners recorded an improvement of 2 minutes and 10 seconds in their top 20 seasonal best times for longer events, translating to a 1.7% increase (52).

Engaging in long-distance running reduces the risk of chronic health issues. However, there is limited evidence for Ethiopian long-distance runners, who are encouraged to avoid lower extremity injuries by adopting preventive measures such as proper recovery, avoiding excessive training distances, and replacing running shoes in a timely manner. Managing competition factors such as distance and frequency, selecting appropriate training surfaces, and using proper footwear can minimize injury risk (53).

Finally, the post-test results of the CTG demonstrated less change across all subgroup analyses, including physical, physiological, and training characteristics of performance indices, compared to the ITG and PTG. However, the combined effects of interval and power training methods revealed significant changes in strength endurance, speed endurance, and RE.