Double threshold training means completing two controlled threshold sessions on the same day, usually one in the morning and one in the afternoon or evening. Because the combined workload draws heavily on muscle glycogen, the day only works if you eat carbohydrate before, during and between both sessions and replace the fluid and sodium you lose. Get the fuelling right and the second session feels as controlled as the first. Get it wrong and it turns into a flat, laboured effort that adds fatigue without the training effect you were after.

Below: how much carbohydrate each session needs, what to eat in the gap, hydration, and a practical timeline for running, cycling or triathlon.

What is double threshold training?

Double threshold training splits a large volume of threshold work into two moderate sessions on one day, rather than one long and demanding session. Both sessions are held at or just below your lactate threshold, the intensity at which lactate begins to build up in the blood faster than your body can clear it.

Two shorter blocks let you accumulate more time near threshold while keeping each one under control. The effort should feel sustained but repeatable, roughly 6 to 7 out of 10, never a race effort.

An example structure for a well-trained athlete:

• Morning session — longer intervals at the lower end of threshold, for example 4 to 6 x 8 minutes with short, easy recoveries
• Afternoon session — shorter, slightly quicker repetitions, for example 8 to 12 x 3 minutes, still controlled
• Either side of each set — an easy warm-up and a relaxed cool-down so the total session lasts around 60 to 75 minutes

Intensity is guided by blood lactate, heart rate, pace or power and perceived effort combined. There is no single lactate value that marks threshold for everyone, so set targets from your own testing.

The method suits experienced athletes with a deep aerobic base and a consistent training history. It belongs in a specific preparation block, for example ahead of a spring city marathon, a summer gran fondo or a long-course triathlon, and it is not a starting point for newer athletes.

SHOP FUEL, HYDRATION & RECOVERY

BUILD YOUR FREE FUEL PLAN

Why does double threshold training demand so much carbohydrate?

Threshold intensity relies heavily on carbohydrate for energy, so two sessions in one day can leave glycogen stores substantially lower by the time the second session starts.

Start the afternoon session with low glycogen and the target pace or power feels harder at the same heart rate, technique slips and the effort creeps above threshold, the opposite of the controlled stimulus the method relies on.

Over weeks, repeated under-fuelling also raises the risk of low energy availability, a state linked in research to slower recovery, hormonal disruption, more frequent illness and injury.

On a double threshold day, sports nutrition guidance generally points to 6 to 10 g of carbohydrate per kg of body weight across the day. For a 70 kg athlete, that is roughly 420 to 700 g, spread across meals, snacks and the sessions themselves.

How much carbohydrate per hour do you need in each session?

For threshold sessions of 60 to 90 minutes, aim for 30 to 60 g of carbohydrate per hour, moving towards the upper end for the second session.

• Morning session — 30 to 45 g per hour is usually enough after a carbohydrate-based breakfast
• Afternoon session — 45 to 60 g per hour, starting early in the main set rather than waiting until you fade
• Longer cycling sessions over 90 minutes — 60 to 90 g per hour using a glucose and fructose blend, built up gradually in training
• Running at threshold — gels and drink mix are easier to manage than solid food at this pace

A simple approach is one 30 g gel at the start of the main set, with a carbohydrate drink sipped through the session. A PF 30 Gel provides a measured 30 g, which makes hourly targets easy to track.

Practise your target intake in training. The gut adapts to regular carbohydrate intake during exercise, so a double day is a useful chance to rehearse race fuelling.

What should you eat between the two sessions?

Start refuelling within 30 to 60 minutes of finishing the first session, aiming for around 1 to 1.2 g of carbohydrate per kg of body weight per hour for the first three to four hours, plus 20 to 30 g of protein. This applies when the gap is shorter than about eight hours.

For a 70 kg athlete, that is roughly 70 to 85 g per hour, easier to reach with frequent smaller intakes than one large meal.

• Straight after session one — a carbohydrate drink or recovery shake with fluid and sodium
• Main meal two to three hours before session two — rice, pasta, potatoes or bread with a lean protein source, moderate in fibre and fat
• Top-up snack 60 to 90 minutes before session two — a banana, rice cakes, a real-food energy bar or a gel
• What to avoid — large high-fat or high-fibre meals close to the afternoon session

Carbohydrates contribute to the recovery of normal muscle function after highly intensive or long-lasting exercise that leads to muscle fatigue and depleted glycogen stores, and protein contributes to the maintenance of muscle mass.

How should you manage hydration and electrolytes on a double threshold day?

Start each session well hydrated, drink to manage thirst during it, and replace roughly 125 to 150 percent of the fluid you lost in the hours after the first session. Weighing yourself before and after a session gives a reliable estimate, since 1 kg of body mass lost is close to 1 litre of fluid.

Sweat sodium concentration varies widely between athletes, so a fixed amount suits few people.

• Light or less salty sweaters — around 500 mg of sodium per litre of fluid
• Heavy or salty sweaters, hot conditions or indoor trainer sessions — 1,000 to 1,500 mg of sodium per litre
• Scandinavian winter — outdoor losses drop, but indoor trainer and treadmill sessions often bring the highest losses of the year

PH 1000 Electrolyte Tablets deliver 1,000 mg of sodium per litre, a practical option for heavier sweaters. If you prefer fuel and fluid in one bottle, a Carb & Electrolyte Drink Mix covers both. Carbohydrate-electrolyte solutions contribute to the maintenance of endurance performance during prolonged endurance exercise and enhance the absorption of water during physical exercise.

A practical double threshold training fuelling protocol

This timeline assumes a morning session at around 07:00 and an afternoon session at around 17:00. Scale the amounts to your body weight.

1. The evening before — a carbohydrate-focused dinner so you start the day with topped-up glycogen
2. Two to three hours before session one — breakfast providing 1 to 2 g of carbohydrate per kg, such as porridge, toast with honey and a banana, with around 500 ml of fluid. With an early start, eat a smaller 1 g per kg breakfast 60 to 90 minutes before
3. During session one — 30 to 45 g of carbohydrate per hour and 500 to 750 ml of electrolyte drink per hour, adjusted for conditions
4. Within an hour of finishing — around 1 g of carbohydrate per kg plus 20 to 30 g of protein, with fluid and sodium
5. Midday — a carbohydrate-rich main meal with lean protein, keeping fibre and fat moderate
6. 60 to 90 minutes before session two — a 30 to 60 g carbohydrate snack and a bottle of electrolyte drink
7. During session two — 45 to 60 g of carbohydrate per hour, starting early in the main set
8. Evening — a balanced dinner with carbohydrate, protein and vegetables

If you use magnesium as part of your evening routine, Triple Magnesium Tablets provide a convenient option. Magnesium contributes to normal muscle function and to the reduction of tiredness and fatigue.

When should you skip or shorten a double threshold day?

If you cannot hold the target intensity without your heart rate or perceived effort climbing, end the session early. A shortened, controlled session beats a completed one that drifted into hard training.

• Returning from illness or injury — reintroduce single threshold sessions before doubling up
• Signs of low energy availability — persistent fatigue, poor sleep, frequent illness or stalled progress call for more fuel, not more sessions
• Heavy work or travel weeks — one well-executed session beats two compromised ones

Frequently asked questions

Can I do double threshold training on a low-carbohydrate diet?

It is not recommended. Threshold intensity depends heavily on carbohydrate, and a low-carbohydrate intake makes it difficult to restore glycogen between sessions. The likely result is a second session that drifts above threshold or falls short of target. If you train with low carbohydrate availability at times, keep it to easy sessions.

How long should the gap between the two sessions be?

Most athletes leave six to nine hours between sessions, and at least four. A longer gap gives more time to refuel and rehydrate, which helps the second session stay controlled. With a shorter gap, prioritise frequent carbohydrate intake straight after the first session and keep the pre-session meal light and easy to digest.

Do I need gels for a 60-minute threshold session?

Not always for a single session, but on a double day they help. A gel or carbohydrate drink in the morning session limits how far glycogen falls, and fuelling during the afternoon session is strongly advisable. Around 30 to 60 g per hour is a practical target, depending on session length and how depleted you feel.

Is double threshold training suitable for triathletes?

Yes, for experienced triathletes with a solid aerobic base. Many keep the threshold work to one discipline per day, such as running in the morning and running or cycling in the afternoon, while swimming stays easy. Overall training load is higher across three sports, so careful fuelling and recovery between sessions matter even more.

How do I know if I under-fuelled between sessions?

Common signs include a higher heart rate or perceived effort at the usual pace or power, heavy legs early in the second session, poor concentration and strong cravings afterwards. If this happens regularly, increase carbohydrate intake in the first hours after session one and add a snack 60 to 90 minutes before session two.

SHOP FUEL, HYDRATION & RECOVERY

BUILD YOUR FREE FUEL PLAN

Stay reflective. Train smarter. Race faster.