Magnesium is an essential nutrient that supports many biological functions—particularly those involved in physical performance. From muscle contraction to energy production and recovery, magnesium plays a key role in helping your body perform and bounce back after workouts.

During exercise, your body uses more magnesium, and if levels are too low, you may experience fatigue, cramping, or slower recovery. This is why athletes and active individuals may benefit from higher magnesium intake—sometimes 10–20% more than the general population.

But when should you take magnesium to support your training—before or after a workout? Here's what the science says.

Why Magnesium Matters for Physical Activity

Magnesium helps regulate calcium and glucose, two critical components of muscle function and energy metabolism. It also supports aerobic performance by improving oxygen delivery and anaerobic performance by helping control lactic acid buildup—both of which can affect stamina and post-exercise soreness.

Low magnesium can lead to:

  • Muscle tightness and cramps

  • Increased fatigue

  • Slower recovery

  • Poor glucose regulation

Ensuring adequate magnesium intake can make a noticeable difference in performance, especially during longer or more intense training sessions.

Taking Magnesium Before Exercise

Some evidence suggests that taking magnesium before your workout may reduce muscle fatigue and delay the build-up of lactate—a byproduct of anaerobic exercise that causes burning and fatigue.

In one study, competitive cyclists who supplemented with 400 mg of magnesium daily throughout a multi-day event showed improved muscle strength and reduced muscle tension, suggesting enhanced performance and faster recovery.

Magnesium may be especially beneficial during interval-heavy or high-intensity workouts, like sprinting or spin classes, where both aerobic and anaerobic systems are taxed.

Taking Magnesium After Exercise

Although there's limited research directly comparing pre- vs. post-workout magnesium timing, maintaining optimal magnesium levels after training may support muscle repair, reduce soreness, and promote restful sleep—all important for recovery.

Some studies indicate that ongoing magnesium supplementation may help reduce delayed onset muscle soreness (DOMS), even if taken after workouts. However, more conclusive data is still needed.

How Much Magnesium Do You Need?

Daily magnesium needs vary based on age, gender, and activity level. General recommendations are:

  • Women: 310–320 mg/day

  • Pregnant women: 350–360 mg/day

  • Men: 400–420 mg/day

Athletes or individuals with intense routines may benefit from 300–500 mg/day, either through food or supplements.

Best Forms of Magnesium for Absorption

Not all magnesium supplements are created equal. These types tend to be better absorbed:

  • Magnesium citrate – often used for muscle recovery

  • Magnesium chloride

  • Magnesium lactate

Less absorbable options like magnesium oxide or magnesium sulfate may not be as effective for athletic recovery, although they’re still used in specific contexts (e.g., as laxatives or in Epsom salt baths).

Natural Food Sources of Magnesium

Incorporating magnesium-rich foods can help maintain daily requirements. Good sources include:

  • Pumpkin seeds

  • Chia seeds

  • Almonds and cashews

  • Spinach and edamame

  • Soy milk

  • Black beans

  • Brown rice

  • Peanut butter

  • Dark chocolate

Considerations and Cautions

Some medications—like diuretics, proton pump inhibitors (PPIs), and antibiotics—can interfere with magnesium absorption or increase its loss. Additionally, magnesium can affect how your body processes certain medications, so consult a healthcare provider before starting supplements.

People assigned female at birth may also experience magnesium fluctuations due to hormonal shifts during the menstrual cycle, particularly in the follicular and luteal phases. This might explain increased cravings for chocolate, a magnesium-rich food, during certain parts of the cycle.

Quick Summary

Magnesium plays a key role in energy production, glucose metabolism, muscle recovery, and overall athletic performance. While there’s no universally agreed-upon "best" time to take magnesium, both pre- and post-workout supplementation may be beneficial—especially for individuals with low dietary intake or those doing intense training.

Whether you choose to take magnesium before a workout to support performance or afterward to enhance recovery, the most important factor is ensuring your magnesium levels are consistently adequate.