Your Body's Internal Clock
Beyond our 24-hour circadian rhythm that governs sleep, our bodies also operate on shorter, repeating cycles known as ultradian rhythms. These cycles, which typically last around 90 to 120 minutes, influence our energy, focus, and cognitive performance
throughout the day. During each cycle, we move from a period of high-energy focus to a period of rest and recovery. Understanding this natural ebb and flow is key. Pushing through the low-energy troughs without a break can lead to diminishing returns, while aligning tasks with our high-energy peaks can boost productivity. In a fitness context, this rhythm helps explain why we might feel a surge of energy at the start of a long workout and a distinct need for a mental and physical reset around the 90-minute mark.
The Endurance Frontier
For endurance athletes, the 90-minute mark is a well-known physiological frontier. This is often the point at which the body's readily available carbohydrate stores, known as glycogen, begin to significantly deplete. This can lead to the dreaded feeling of "hitting the wall," where performance drops dramatically. Exercising for over 90 minutes teaches the body crucial lessons in fuel management. It forces a greater reliance on fat for energy and highlights the importance of strategic nutrition and hydration to sustain effort. For runners and cyclists, longer sessions are where the body learns to become more efficient, improving its ability to transport oxygen and manage metabolic byproducts over extended periods.
Strength, Skill, and Focus
The conversation isn't just about endurance. While many strength training sessions are shorter, aiming for around 45 to 60 minutes for muscle growth, the 90-minute concept still holds relevance. Recent research has highlighted the significant health benefits of accumulating 90 minutes of strength training per week. Studies show this amount of resistance training is linked to a lower risk of early death from all causes, including heart disease and neurological conditions. Mentally, maintaining form and focus through a longer, structured workout builds discipline. Just as a football team must manage its strategy over a full 90-minute match, a longer fitness session challenges your ability to stay engaged, execute movements correctly, and push through mental fatigue.
Making 90 Minutes Work for You
This doesn't mean every workout needs to be 90 minutes long. Shorter, high-intensity sessions of 20 to 30 minutes are incredibly effective and often more practical for a busy schedule. The value of the 90-minute conversation is in its application as a flexible framework. It can be a weekly goal for total strength work, broken into three 30-minute sessions. It could be a single, longer session on the weekend—a long run, a hike, or an extended yoga practice—that focuses on endurance and mental stamina. Or it can be a way to structure a single workout: a 15-minute warm-up, a 60-minute main set, and a 15-minute cool-down and stretch. The key is to listen to your body and use time as a tool to achieve your specific goals, whether they're related to strength, heart health, or mental well-being.
