🚴 Does HIIT build more muscle than steady cardio?

Endurance exercise is great for your heart and lungs, but what about your muscles?

Researchers compared two popular training styles over two weeks:

• HIIT: Short bursts of intense effort with recovery periods.

• MICT: Moderate-intensity continuous cycling.

Each of the 10 participants trained one leg with HIIT and the other with MICT. Both workouts were matched for total time and volume.

Scientists measured myofibrillar protein synthesis: a key marker of muscle building.

The results:

• Both HIIT and MICT improved fitness (VO₂ peak and leg strength).

• Muscle protein synthesis? No difference. Neither HIIT nor MICT increased it compared to the control period, where participants just did their usual daily activity.

What does this mean?

1. Even high-intensity endurance exercise isn’t a stronger driver for muscle growth compared to daily physical activity.

2. It supports long-term research showing that cardio, regardless of intensity, has little impact on increasing lean muscle mass.

🥊 Summary

If your goal is muscle growth, cardio alone - whether HIIT or steady - won’t cut it. Resistance training remains the gold standard for building muscle.

🍞 Eating carbs before exercise part #1: does it limit training benefits?

Many athletes fuel up with carbs before a workout to boost energy. But could this habit actually reduce some of the benefits of training?

Studies show that high carbs availability before exercise can blunt certain adaptations in skeletal muscle and whole-body metabolism.

These adaptations include improvements in fat utilisation and metabolic flexibility; key factors for endurance performance and overall health.

Why does this happen? When carbs are readily available, your body relies more on carbs metabolism and less on fat metabolism during exercise. Over time, this may limit the signals that promote fat-burning efficiency.

The twist

It’s not just about carbs. High carb availability usually means low fat availability, so researchers couldn’t tell whether the effect was due to carbs themselves or the lack of fat. This makes it tricky to separate the independent roles of each nutrient.

What does this mean?

• If your goal is maximising endurance adaptations, occasionally training with lower carbs availability (sometimes called “train low”) might help your body become better at burning fat.

• However, this approach isn’t for everyone. It can increase fatigue and reduce workout intensity, so it’s best used strategically—not before every session.

🥊 Summary

Carbs before exercise give you energy, but they may reduce some long-term metabolic benefits. For most people, a balanced approach works best: fuel properly for high-intensity sessions, and consider lower-carb training for specific endurance goals.

🔍 Eating carbs before exercise part #2: does it alter muscle signalling?

Researchers designed a clever experiment to separate the influence of carbs from fatty acid availability.

They used niacin to suppress fat availability without changing insulin levels, allowing them to isolate the role of carbs.

Participants exercised under three conditions:

• Fasted

• Carbs consumed before exercise

• Niacin taken before exercise (low fat availability)

The results

• Eating carbs blunted a key signalling process in muscle—ACC phosphorylation—compared to both the fasted state and the niacin condition.

• Niacin (low fat availability) did not blunt this signalling, even though fat was suppressed.

What does this mean?

The dampening effect on muscle signalling after exercise is due to high carbs availability, not simply the lack of fat.

This signalling is important because it helps regulate how muscles adapt to training, particularly in terms of energy use and endurance.

🥊 Summary

Carbs before exercise can reduce some of the molecular signals that promote endurance adaptations. If your goal is to maximise these benefits, occasionally training in a fasted state or with lower carb intake might help; but it should be done strategically and not at the expense of workout quality.