Endurance doesn’t work “magically” through single ingredients. The most reliable way to improve performance is to plan training stimuli (volume, frequency, intensity) and thereby trigger appropriate adaptations. Supplements can help in specific situations—but the overall evidence is heterogeneous and rarely as consistent as training research.
Why endurance first needs training instead of supplements
If you want to improve endurance, training and intensity management are stronger and more consistent levers than individual supplements. The evidence for training adaptations is broader and more robust: systematic reviews show typical patterns in how intensities are distributed. In contrast, supplement effects often come from smaller, context-dependent RCTs and are not consistently as large across settings.
The core is physiologically straightforward: endurance performance comes from adaptations in energy metabolism, efficiency, neuromuscular recruitment, inflammatory and recovery processes, and—depending on the sport—also cardiorespiratory performance. Such adaptations are primarily driven by repeated, dosed stressors. That’s exactly why lifestyle levers like sleep, movement outside training, light/circadian rhythm, and appropriate nutrition with sufficient energy are so relevant—they determine whether training stimuli actually “work” or fizzle out.
How big the gap is can be seen indirectly by how consistently training and intensity patterns appear in review literature. For example, (Campos et al., 2022, PMID 34749417) systematically analyzes how training intensities are distributed in middle- and long-distance runners. This supports the practice of not thinking only in terms of “easy vs. hard,” but instead using structured stimulus distribution.
Supplements can still be meaningful—but more as context-dependent fine-tuning: e.g., carbohydrates in heat, certain nutrient lipids in specific target constructs, or interventions in rehabilitation contexts. At the same time, if the evidence in reviews is not strong and homogeneous, caution is warranted with “universal promises.” That’s why many evidence-based approaches prioritize training planning and energy/nutrition logic first—and only then test supplements as a hypothesis.
Training intensity: What the systematic review suggests about distribution
For endurance, training intensity is often organized using structured distribution across multiple intensity zones. A systematic review by (Campos et al., 2022, PMID 34749417) evaluates what intensities typically look like in research among middle- and long-distance runners and which distribution patterns dominate. Direct Answer: The literature supports that endurance training is usually not implemented as “one intensity,” but as a mixture—and that’s what your planning should reflect, as long as it fits your level.
What does this mean practically? First: intensity management influences which adaptations you mostly “feed.” More hard intervals promote specific stimulus characteristics (e.g., neuromuscular/performance-related adaptations), while much lower intensity enables more total work and supports recovery between sessions. Second: the best distribution depends on goals (e.g., 10 km vs. marathon), training status, available time window (how many weeks), and the ability to recover.
The key takeaway from a review perspective: Campos et al. (2022, PMID 34749417) do not show “one single percentage” that is perfect for everyone. Instead, these overview papers clarify that there are typical patterns—but generalizability is not 1:1. For planning, this means you shouldn’t copy a percentage blindly; rather use the logic: sufficient base (for volume and adaptation), targeted hard stimuli (for performance development), and recovery/balancing portions in between so that you actually train the relevant weekly and monthly stimuli.
If you are already working on training planning, it can be useful to view the idea of periodization as a system. In line with that, it can also help to look at carbohydrate periodization for performance-relevant stress (see Carbohydrate periodization: effects & evidence up to meta-analysis)—but intensity remains the foundation because it provides adaptive “control.”
Short summary: The most evidence-aligned conclusion is structural: endurance training is typically distributed in an intensity-based way in the literature. Your plan should translate that into a flexible, goal- and level-appropriate stimulus distribution.
Heat, carbohydrates, and endurance: systematic evidence with a practical focus
Carbohydrates can support endurance performance in heat, because heat and limited available energy together reduce performance. A systematic review by (Salame et al., 2026, PMID 42105255) summarizes studies on how carbohydrates influence endurance performance in heat. Direct Answer: Overall, the evidence suggests carbohydrates are especially relevant when heat further makes performance harder—however, the exact effect magnitude depends on protocols, temperature, and the sport/exercise format.
Why this matters for practice: In heat, perception, thermoregulation, and metabolic stress change. Carbohydrates can help stabilize available energy during exercise and thereby delay the drop in performance. The strength of a systematic approach lies in combining many studies and identifying patterns—not in guaranteeing a “magical single dose” for all situations.
However, transferability matters: Salame et al. (2026, PMID 42105255) show through the summary that this is not just theoretical. Still, studies can differ substantially, for example in:
- temperature range and duration of the exercise,
- sport (running vs. cycling/other protocols),
- form and timing of carbohydrate intake (during vs. before training),
- training status and performance level of participants.
This leads to a practical, not overblown recommendation: if your training or competition occurs in hot conditions and intensity/exercise duration truly limit performance, carbohydrates are typically the first nutrition lever you should prioritize based on data. This also aligns with the general principle: first energy availability and fluid/electrolyte logic, then the finer points via supplements.
If you also think about circadian rhythm (e.g., training at times of day that interact with heat and sleep), a systematic look can help (see Circadian rhythm: effects & evidence (what is supported)). But for the question “heat + endurance,” the bottom line stays: carbohydrates are a central, evidence-supported component—as long as you account for the specific setting.
Supplements for endurance: what individual RCTs actually cover
Supplements for endurance have shown specific effects in RCTs, but often without broad, universal generalization. Direct Answer: The RCTs in the provided study list test very different mechanisms (Creatin/Caffeine, Creatin combined with Plyometrics, EPA/structured lipid) and examine different endpoints. Therefore, while the results are interesting, the overall evidence is heterogeneous and not automatically transferable to “every endurance target group.”
One example is (Pakulak et al., 2022, PMID 33759701): it investigates Creatin and Caffeine in the context of repeated resistance training—not as a pure endurance “therapeutic.” The study output includes, among other things, strength, endurance, and ratings of workload and exhaustion. Important for your interpretation: if an RCT tests endurance endpoints within a strength-training context, that does not necessarily translate 1:1 to true endurance training (running/cycling at defined intensities).
Further, (Ramírez-Campillo et al., 2016, PMID 26778661) reports effects of a combination of plyometric training and Creatin in female soccer players—focused on maximal-intensity and endurance-related performance level. Again, the sport and training design are part of the “intervention.” This makes the results potentially transferable to athletes with similar game-sport characteristics, but not as a general endurance supplement recommendation for every target group.
Finally, (Shimizu et al., 2026, PMID 41992745) examines after eight weeks of EPA plus a structured lipid (MCT “structured lipid”) the EPA/AA ratio and muscle performance in young men. This is relevant because it couples an achievable nutrition-based target marker (EPA/AA) with performance endpoints. Still, this is not a classical endurance endpoint, but rather a performance/muscle-focused framework.
Supplements and endpoints in the RCTs: what was tested
| Intervention | Timing / setting | Tested endpoints (examples from the RCTs) |
|---|---|---|
| Creatin + Caffeine | Within resistance training; trained young adults | Body composition, strength, endurance, workload and exhaustion ratings (Pakulak et al., 2022, PMID 33759701) |
| Plyometric training + Creatin | In female soccer players; maximal-intensity and endurance-related performance level | Maximal-intensity performance level and endurance-related performance measures (Ramírez-Campillo et al., 2016, PMID 26778661) |
| EPA + structured lipid (MCT-“structured lipid”) | 8 weeks in young men | EPA/AA ratio and muscle performance (Shimizu et al., 2026, PMID 41992745) |
| (No supplement, but specialized training) Respiratory muscle training | High-intensity respiratory muscle training; Parkinson patients | Maximal inspiratory pressures, respiratory endurance, dyspnea, and physical performance (Brito et al., 2026, PMID 41933952) |
What you can practically take away: in this evidence landscape, supplements are not the main pillar. They are more like “targeted add-ons” that may work depending on the endpoint and sport setting. For endurance goals, the priority remains: training stimuli + intensity management + (in heat) a carbohydrate-focused nutrition strategy.
Evidence hierarchy: RCT, systematic review, and what the data means
If you want to decide what for endurance is “truly supported,” you have to read evidence level correctly. Direct Answer: Systematic reviews like (Campos et al., 2022, PMID 34749417) and (Salame et al., 2026, PMID 42105255) are often the best starting point because they summarize many studies and make patterns more stable. Individual RCTs provide valuable clues, but they depend more strongly on the population and study design.
The advantage of systematic reviews is that you get an aggregated view of multiple studies. That doesn’t mean everything automatically has the same effect size—but the overall direction is more robust. Campos et al. (2022, PMID 34749417) makes this concrete through training intensity distribution: which patterns dominate the literature and how intensity is typically organized in middle- and long-distance training. Such patterns are strong arguments for making training planning non-random.
Salame et al. (2026, PMID 42105255) bundles the question of carbohydrates in heat. Again: this systematic collection increases the likelihood that you are not just seeing a random effect. Still, transferability is limited because heat and exercise protocols are not identical across studies.
Individual RCTs are still useful—just interpret them differently than reviews. This is especially true for supplements or specialized interventions. Example: in Parkinson’s disease, high-intensity respiratory muscle training is tested; this is an intervention to improve breathing mechanics and exercise tolerance, not classic endurance training. (Brito et al., 2026, PMID 41933952) reports improvements in maximal inspiratory pressures, respiratory endurance, dyspnea, and physical performance. This can be meaningful for rehabilitation and special populations, but it is not easily generalized to “healthy endurance athletes.”
Additionally, (Henriksson et al., 2026, PMID 42097659) shows in an RCT from Phys-Can data on adherence in (neo-)adjuvant chemotherapy that the feasibility of an exercise program is a key factor. This matters because performance improvement depends not only on “effectiveness,” but also on whether the program is actually followed.
Bottom line from this evidence logic: use reviews to understand the range and direction. Use RCTs to test opportunities and limitations in specific target groups—but avoid deriving universal promises from them.
Rehabilitation and special populations: endurance as a goal beyond sport
Endurance is not only an athlete goal. In rehabilitation and special populations, “endurance” can mean coping better with exertion—for example via respiratory muscle function, training adherence, or functional performance. Direct Answer: the study list indicates that interventions addressing breathing or exercise capacity can help measurably in RCTs, but generalizability to typical training plans is limited because the target mechanisms are specific.
A very concrete example is (Brito et al., 2026, PMID 41933952): high-intensity respiratory muscle training improved in a randomized study in Parkinson’s disease not just subjective symptoms (dyspnea), but also objective breathing parameters (maximal inspiratory pressures), respiratory endurance, and physical performance. In practice, this means: if breathing restriction is part of the load-limiting factor, respiratory muscle training can be a direct lever—rather than only “classic cardio” as the default route.
Similarly, (Henriksson et al., 2026, PMID 42097659) in the Phys-Can RCT shows how well participants adhere to a training program during (neo-)adjuvant chemotherapy. Even if this is not formulated identically as an “endurance effect” for a sports competition, adherence is a major determinant of benefit: a program that people don’t stick with cannot produce sustained improvements in performance or function. For rehabilitation logic, this is at least as important as a potential effect size.
For postoperative/neurologic-functional cases, (Núñez-Cortés et al., 2026, PMID 42001196) investigates dual-task resistance training after carpal tunnel surgery and looks at, among other things, muscular endurance and pressure sensitivity. This is also “endurance-related” in a functional sense and indicates that endurance goals can be integrated into rehab questions—but the endpoints and mechanisms differ.
Safety and realism: in special populations you must individualize training stimuli (intensity, progression, monitoring). The study list does not provide general dose limits for “endurance supplements” that apply to all body groups, because these RCTs primarily treat training as the intervention. That is methodologically consistent: training is the main focus, supplements are—if at all—secondary.
What you can take away
- Endurance performance improves most reliably through training planning: especially the distribution of training intensities is supported as a recurring pattern in reviews (Campos et al., 2022, PMID 34749417).
- Supplements are usually context-dependent, and their evidence is more heterogeneous than for training questions (e.g., Creatin/Caffeine or EPA/AA-related interventions in individual RCTs such as Pakulak et al., 2022, PMID 33759701; Shimizu et al., 2026, PMID 41992745).
- In heat, carbohydrates are an important nutrition lever, supported by systematic review evidence (Salame et al., 2026, PMID 42105255)—but details depend on the setting.
- In rehabilitation and special populations, endurance-related goals can also be achieved through specialized training forms, such as respiratory muscle training in Parkinson’s disease (Brito et al., 2026, PMID 41933952).