When physiologist Bengt Saltin described the fundamentals of endurance performance, he and his team shaped the understanding of VO2max and training adaptations. Today, researchers and coaches are expanding this perspective with precision methods that utilize every heartbeat. The idea: “Better is better,” not “more is better.” Those who train their hearts intelligently unlock more energy, longer performance, and robust health, with less time wasted.

Endurance is the ability to sustain a constant level of performance over extended periods because the heart, lungs, and muscles work efficiently together. The heart acts as a pump that transports blood – and thus oxygen – to the muscles. The better this system, the higher the VO2maxmaximal oxygen uptake; measure of cardiorespiratory performance, and the more economical each movement becomes. Key parameters are training intensity, duration, and management. Here, heart rate variability (HRV)fluctuation of time intervals between heartbeats; marker for the recovery state of the autonomic nervous system serves as an early indicator of whether you can endure more load or whether it's time to ease off. Interval training provides targeted high-intensity stimuli that tax the cardiovascular system above the norm and trigger significant adaptations. Fuel is also crucial: Carbohydrates replenish the glycogen storesreadily available carbohydrate reserves in muscles/liver and ensure high intensities. After training, smart recovery accelerates the return to a capable state – a central, often underestimated part of the system.

Well-dosed interval training in water improves blood pressure, resting heart rate, and performance markers – parameters closely linked to cardiovascular health and longevity. Studies have shown that systolic blood pressure and resting heart rate decreased after just weeks of structured swimming programs, while endurance performance significantly increased ^[1]. Even among well-trained athletes, a short HIIT cycle can boost maximal oxygen uptake (VO2max) – a strong predictor of lifespan and quality of life ^[2]. For these effects to occur, sufficient fuel is necessary: A targeted carbohydrate intake before, during, and after exertion stabilizes performance and speeds up the replenishment of glycogen stores, maintaining training quality between sessions ^[3]. For recovery, evidence shows that yoga after intense sessions can elevate parasympathetic activity, calm breathing, and normalize HRV faster than pure stretching – an advantage for a quicker return to resilience ^[4].

Several high-quality studies provide clear guidelines. A randomized study involving previously inactive, premenopausal women with mild hypertension compared high-intensity interval swimming with moderate continuous swimming over 15 weeks. Both groups improved blood pressure and resting heart rate, but the interval format achieved similar health effects in significantly shorter training time – a compelling argument for efficiency in daily life ^[1]. In competitive sports, a four-week HIIT program for swimmers showed significant gains in both aerobic and anaerobic energy provision as well as VO2max. Relevance: Even among well-trained individuals, adaptability is high when intensity and structure align ^[2]. For training management, precision is crucial: An intervention approach combining heart rate variability, resting heart rate, and subjective well-being resulted in greater performance gains in cyclists compared to HRV-guided training alone. The essence: Multidimensional, everyday data improve individual training fine-tuning and therefore the results ^[5]. Additionally, a systematic review emphasizes that personalized carbohydrate strategies before, during, and after exertion stabilize endurance performance and secure the recovery of glycogen stores between sessions – the key to maintaining training quality ^[3].

- Incorporate 1–2 HIIT swimming sessions per week: for example, 6–10 × 30 seconds of fast to very hard swimming, each followed by 2 minutes of easy rest. This provides strong cardiovascular stimuli in a manageable time and improves blood pressure, resting heart rate, and endurance ^[1]. For advanced athletes, 4–6 weeks of focused HIIT can yield additional VO2max gains ^[2].
- Control intensity with a heart rate monitor: Determine your endurance zones (e.g., via a field test) and deliberately train intervals in higher zones, while base units are in moderate zones. Supplement monitoring with daily HRV, resting heart rate, and a brief well-being check-in to individually adjust load/recovery and accelerate progress ^[5].
- Secure energy with a smart carbohydrate strategy: Eat carbohydrate-rich, well-tolerated foods before longer or more intense sessions; utilize readily available carbohydrates for sessions lasting more than 60–90 minutes; focus on timely post-workout intake for glycogen replenishment. This ensures high training quality throughout the week ^[3].
- Actively recover: After HIIT sessions, schedule 10–15 minutes of yoga with calm breathing. This promotes parasympathetic activity, lowers respiratory rate, and stabilizes HRV faster than stretching alone – ideal for being ready again the next day ^[4].

The future of endurance training is data-informed, personalized, and efficient: short, targeted stimuli, precise management, and smart recovery. With better sensors and analytics, daily fine-tuning will become even more accurate – your heart training will adapt in real time to further maximize health, energy, and longevity.