Conquering Muscle Cramps: A Sports Physiotherapist’s Guide for Trail Runners and Endurance Athletes

As a sports physiotherapist working with trail runners, ultra-marathoners, triathletes, cyclists and other endurance athletes, I’ve heard the stories of muscle cramps derailing countless races and training sessions. Whether it’s a calf, quad & hamstring seizing on Mt Solitary or both hamstrings locking up whilst riding up the back of falls creek, exercise-associated muscle cramps (EAMC) are a frustrating reality. The good news? Science and clinical experience offer clear insights into why cramps strike and how to prevent them. Drawing on peer-reviewed research and my work with athletes & colleagues like Dr Rebecca Haslam & Belle Smith (Dietitians), this guide unpacks the causes of cramps—focusing on sodium depletion, muscle fatigue, and unaccustomed efforts—and provides actionable strategies to keep you moving strong on trails and beyond.

The Electrolyte Equation: Sodium Depletion and Muscle Chaos

Endurance events, especially trail running’s long, sweaty slogs through heat, humidity, or high altitude, drain your body of critical electrolytes—sodium, potassium, magnesium—via sweat. When losses outpace replacement through sports drinks, salt tablets, or gels, your muscles can revolt with cramps.

Sodium: The Primary Culprit

Sodium is vital for muscle function, maintaining the electrical charge that allows muscles to contract and relax. A seminal study by Bergeron (2003) in Sports Medicine highlights that significant sodium losses during prolonged exercise correlate strongly with EAMC. Trail runners and ultra-marathoners, who may sweat 1–2 L/hour with sodium concentrations of 20–80 mmol/L, can lose up to 6 grams of sodium in just three hours. Compare that to a typical salt tablet (0.3–0.6 g sodium), and it’s clear why replacement often falls short. Hoffman and Stuempfle (2015) in International Journal of Sport Nutrition and Exercise Metabolism found that even ultra-runners using sodium supplements cramped when sweat losses were extreme, underscoring the challenge of keeping up.

Sorry for the science jargon: at the muscle level, sodium depletion disrupts the sarcolemma’s (located in muscles) resting membrane potential, reducing the sodium gradient needed for smooth action potential (or electrical signal) propagation via the nerves. This hyperexcitability can trigger involuntary contractions—cramps. Moss et al. (2011) in Journal of Strength and Conditioning Research reported lower post-race serum sodium in cramp-prone athletes, reinforcing this link.

Magnesium and Other Electrolytes

Magnesium, while less depleted by sweat, plays a supporting role. It regulates calcium uptake in the sarcoplasmic reticulum (located within muscle cells), which governs muscle contractions. A deficiency—possible from poor diet or extreme endurance stress—can lead to uncontrolled calcium release, sparking cramps. Nielsen and Lukaski (2006) in Magnesium Research note that while magnesium losses are minimal, marginal deficiencies may still destabilise muscle function over long efforts. Potassium and calcium imbalances are less directly implicated but can exacerbate issues, particularly when dehydration compounds the problem (Schwellnus et al., 2008, British Journal of Sports Medicine).

The Limits of Electrolyte Replacement

While salt tablets and electrolyte drinks are staples, they’re not a panacea. Hoffman’s research suggests that replacing sodium at the rate of extreme losses is logistically difficult and risks gastrointestinal distress. As a physiotherapist, I recommend athletes undertake a sweat test with our resident Dietitians, Belle & Bec. This removes the guess work and allows you to go into hard training sessions and events with a clear plan regarding sodium & electrolyte replacement.

Neuromuscular Fatigue: When Trails Push Muscles to the Brink

Trail running’s rugged terrain—steep climbs, technical descents, and uneven surfaces—demands more from your muscles than road running or cycling. Combine that with the sheer duration of endurance events, and neuromuscular fatigue becomes a prime cramp trigger. Schwellnus et al. (2011) in Current Reviews in Musculoskeletal Medicine propose that EAMC often stems from altered neuromuscular control, especially when muscles are pushed beyond their trained capacity.

The Physiology of Fatigue-Induced Cramps

Prolonged exercise disrupts the balance between excitatory and inhibitory signals in your muscles. Muscle spindles, which promote contraction, become hyperactive, while Golgi tendon organs, which inhibit excessive force, fatigue and lose their dampening effect. This imbalance can cause a muscle to lock into a sustained contraction—a cramp. For trail runners, this might happen late in a race when quads are trashed from descents or calves are screaming after hours of toe-pointing climbs.

Muscle Weakness and Unaccustomed Efforts

In my clinic, I often see cramps tied to weaknesses in specific muscle groups, especially when athletes tackle unaccustomed intensity or duration. A trail runner with underdeveloped glutes may over-rely on calves, leading to fatigue and cramps. Wagner et al. (2010) in Journal of Athletic Training found that cramp-prone athletes had lower baseline strength in affected muscles, suggesting that targeted strength training can reduce risk. For example, a triathlete transitioning from bike to run may cramp if their hamstrings aren’t conditioned for the shift in mechanics.

Additional Cramp Triggers in Endurance Sports

Research identifies other factors that can tip the scales toward EAMC, particularly relevant for trail runners and endurance athletes:

• Dehydration: While not the primary cause, dehydration reduces muscle perfusion and amplifies electrolyte imbalances, increasing cramp risk. Sawka et al. (2007) in Medicine & Science in Sports & Exercise note that fluid losses exacerbate neuromuscular irritability, especially in hot races.

• Environmental Stressors: Heat and humidity accelerate sweat losses, while cold trails can stiffen muscles, reducing flexibility. Bergeron (2008) emphasises acclimatization to race conditions—crucial for events like Mt Solitary Ultra & UTA.

• Pacing Errors: Starting too fast or under-tapering depletes glycogen and fatigues muscles early, inviting cramps. Noakes (2012) in Waterlogged highlights pacing as a critical factor for endurance success.

• Genetic Factors: Emerging evidence, such as O’Connell et al. (2013) in Journal of Sports Sciences, suggests some athletes may have a genetic predisposition to cramps, possibly linked to ion channel dysfunction. While not yet actionable, this underscores individual variability.

Clinical Strategies to Prevent and Manage Cramps

As a sports physiotherapist, my goal is to empower you with evidence-based tools to minimise cramps and maximise performance. Here’s how to stay cramp-free on the trails or in your next endurance event:

• Personalised Nutrition: Develop a fueling plan tailored to your sweat rate and race conditions. Aim for 0.5–1 g sodium/hour via sports drinks, gels, or salt tablets, but practice in training to avoid GI issues. Definitely consider sweat testing for precision.

• Strength and Conditioning: Incorporate strength training 2 times weekly, focusing on trail-specific muscles (glutes, hamstrings, calves). Exercises like lunges, deadlifts, and eccentric calf raises build resilience against fatigue.

• Terrain-Specific Training: Replicate race demands in training—hilly trails for mountain ultras, bike-to-run transitions for triathlons. This conditions muscles for the real thing, reducing unaccustomed stress.

• Smart Pacing: Start conservatively, especially in ultras or multi-hour events, to preserve muscle glycogen and delay fatigue. Work with a coach or use heart rate zones to guide effort. VO2 testing with Lucas McBeath will accurately define these zones.

• Race-Day Prep: Acclimatise to heat or altitude if racing in extreme conditions. Pack portable electrolytes (chews or tabs) for easy trail access. Secure them in zip pockets so that you don't accidently drop them on Mt Solitary!! I'll let Clarkey tell that story.

• Cramp First Aid: If a cramp hits, pause and gently stretch the muscle (e.g., straighten your leg and dorsiflex your foot for a calf cramp). Rehydrate whilst walking or reducing your pace. Take in some salt tablets & electrolytes, and ease back into movement. Pickle juice may also help.

• Post-Race Recovery: Refuel with nutrient-rich foods, hydrate, and use foam rolling or light stretching to restore muscle function. Schedule a physio check-up to assess for imbalances or weaknesses if this continues to occur.

Conclusion: Run Strong, Cramp Less

Muscle cramps don’t have to sabotage your trail runs or endurance races. Sodium depletion, neuromuscular fatigue, and unaccustomed efforts are the primary drivers, but with a strategic approach—rooted in research and tailored to your needs—you can minimise their impact. As your sports physiotherapist, I encourage you to blend smart fueling, targeted strength work, and race-specific training to build a cramp-resistant body. Next time you’re charging through a trail’s switchbacks or pushing through the final leg of a triathlon, you’ll be equipped to outrun cramps and chase your goals.

Key References:

1. Bergeron, M. F. (2003). Sports Medicine, 33(7), 517-529.

2. Hoffman, M. D., & Stuempfle, K. J. (2015). International Journal of Sport Nutrition and Exercise Metabolism, 25(4), 347-352.

3. Moss, K. N., et al. (2011). Journal of Strength and Conditioning Research, 25(6), 1544-1550.

4. Nielsen, F. H., & Lukaski, H. C. (2006). Magnesium Research, 19(3), 180-189.

5. Schwellnus, M. P., et al. (2008). British Journal of Sports Medicine, 42(6), 567-572.

6. Schwellnus, M. P., et al. (2011). Current Reviews in Musculoskeletal Medicine, 4(2), 74-84.

7. Wagner, T., et al. (2010). Journal of Athletic Training, 45(2), 130-137.

Here’s to cramp-free trails and unstoppable endurance!

This is APA Sports Physiotherapist, Darren Glendenning, signing off for now!

You can book an appointment with Darren or Newcastle Knights Physiotherapists Katie or Hayd'n at www.upnadamptphysio.com

Bookings also available on our website for:

• Dietitian - SWEAT TESTING, weight-loss or to optimise your training nutrition / fueling

• VO2 Max testing - to discover more effective ways to train efficiently

• Strength & Conditioning Programs - contact us via the website or email us at upnadamptphysio@gmail.com

• Remedial Massage - to relieve accumulative muscle tension & keep you training well.