Training & Cardio

This content is for informational purposes only and does not constitute medical or nutritional advice. Speak with your health professional before starting this protocol.

Exercise disclaimer: Training during caloric restriction carries an elevated injury risk compared to training at maintenance. Reduce loads where needed, prioritise form, and stop if you experience dizziness, unusual pain, or chest discomfort. Consult your health professional if you have any cardiovascular or musculoskeletal conditions.

Resistance training is central to the Fat Loss Sprint's design. High protein intake and resistance training work together to preserve lean mass during severe caloric restriction. The research below indicates that dropping either one leads to greater muscle loss, a larger fall in resting metabolic rate, and worse body-composition results.

Why Resistance Training Is Central to the Protocol

The body is highly economical during a caloric deficit. Muscle tissue costs approximately 13–30 kcal/kg/day just to maintain at rest (Müller et al., 2009). Without a clear signal that the muscle is needed, your body will break it down for fuel.

Resistance training is that signal. Mechanical tension on muscle fibers activates the mTOR pathway — telling your body that the muscle is functionally necessary and should be preserved. This signal works even under severe caloric restriction. It operates independently of energy status (Hector & Phillips, 2018).

The research is direct on this point:

• Donnelly et al. (1991) studied obese women on a 520 kcal/day diet. The group that added resistance training preserved significantly more lean mass than the diet-only group.
• Bryner et al. (1999) compared resistance training to cardio during an 800 kcal/day diet. After 12 weeks, the resistance training group maintained their lean mass and resting metabolic rate. The cardio group experienced significant declines in both.
• Willoughby et al. (2023) confirmed in a recent review that resistance training is more effective than aerobic exercise for preserving muscle during VLCDs, because it directly stimulates muscle protein synthesis.

Neither high protein alone nor resistance training alone is sufficient; the evidence indicates both are needed together.

Training Principles for Your Sprint

Frequency: 2–3 Sessions Per Week

Recovery capacity is reduced during severe caloric restriction. Your body has fewer resources for muscle repair and glycogen replenishment. Train too often and you compound the problem.

• Minimum: 2 full-body sessions per week
• Optimal: 3 sessions per week
• Maximum: 3 sessions per week. Exceeding this during a Fat Loss Sprint risks overreaching, excess cortisol, and impaired recovery (Helms et al., 2014).

Intensity: Moderate to Heavy

Target 65–80% of your one-repetition maximum, which corresponds roughly to 6–12 reps per set. This range provides sufficient mechanical tension to signal muscle preservation without demanding the neural and metabolic resources that maximal-effort lifting requires.

The protocol discourages 1–3RM maximal lifts, forced reps, and drop sets. Recovery resources are reduced during severe caloric restriction and are not suited to that level of demand.

Volume: Controlled and Reduced

Aim for 8–12 total working sets per muscle group per week, distributed across your 2–3 sessions. Per session, that means 3–4 compound exercises with 2–3 working sets each.

High training volume increases cortisol, depletes glycogen faster, and demands more recovery — all counterproductive during your sprint.

Exercise Selection: Compound Movements First

Compound movements (squat, deadlift, bench press, row, overhead press) recruit large muscle groups and provide the most efficient muscle-preserving stimulus per session. They train multiple muscle groups at once and produce a greater hormonal response than isolation exercises.

Build your sessions around these movements.

Progressive Overload: Maintain, Don't Force Gains

During your sprint, progressive overload means maintaining your current strength as long as possible, not hitting personal bests. Some strength loss is normal and expected during severe caloric restriction. A 5–10% decrease in working weights over a 2–4 week sprint is typical.

If your strength drops, reduce load but protect your sets. Preserving volume (number of sets) matters more for lean mass than preserving load (Helms et al., 2014).

Sample Programs

Full Body, 2x Per Week

Full Body, 3x Per Week

Sprint-Specific Considerations

Warm Up Properly

Reduced glycogen and caloric restriction increase injury risk. Every session needs:

• 5 minutes of light cardio (walking, cycling) to raise core temperature
• Dynamic stretching for the muscle groups you're training
• 1–2 progressive warm-up sets per exercise before working sets

Manage Recovery

The protocol recommends spacing sessions at least 48 hours apart and prioritising 7–9 hours of sleep per night. If recovery feels inadequate, the guidance is to reduce volume (sets) rather than frequency before considering further changes.

When to Pull Back

Reduce to 2 sessions per week and cut working sets by 30–50% if you experience:

• Persistent joint pain beyond normal training soreness
• Strength declining more than 15–20% from baseline
• Inability to complete prescribed sets consistently
• Fatigue lasting more than 48 hours after a session
• Sleep disruption tied to training
• Mood deterioration correlated with sessions

Keep exercise selection and rep ranges the same. Just do less of it.

If You're New to Resistance Training

You can start during your sprint. Use these modifications for the first two weeks:

• Begin with machine-based exercises to learn movement patterns safely
• Use lighter loads (60–65% of estimated 1RM)
• Focus on controlled form, not load
• Start with 2 sessions per week and assess recovery before considering 3

Even in beginners, the muscle-preserving stimulus from resistance training is meaningful during a caloric deficit, provided protein intake is adequate.

Key Takeaways

• The FLS protocol is built around resistance training. Without it, lean mass loss is significantly greater even with adequate protein intake.
• The protocol recommends training 2–3 times per week with moderate-to-heavy loads and controlled volume.
• Compound movements give you the most lean-mass protection per session.
• Your goal during the sprint is to maintain strength, not set records.
• Recovery is impaired. Adjust training when the signs tell you to.

References

Bryner, R. W., et al. (1999). Journal of the American College of Nutrition, 18(2), 115–121. https://doi.org/10.1080/07315724.1999.10718838

Donnelly, J. E., et al. (1991). The American Journal of Clinical Nutrition, 54(1), 56–61. https://doi.org/10.1093/ajcn/54.1.56

Hector, A. J., & Phillips, S. M. (2018). International Journal of Sport Nutrition and Exercise Metabolism, 28(2), 170–177. https://doi.org/10.1123/ijsnem.2017-0273

Helms, E. R., Aragon, A. A., & Fitschen, P. J. (2014). Journal of the International Society of Sports Nutrition, 11(1), 20. https://doi.org/10.1186/1550-2783-11-20

Longland, T. M., et al. (2016). The American Journal of Clinical Nutrition, 103(3), 738–746. https://doi.org/10.3945/ajcn.115.119339

Müller, M. J., Bosy-Westphal, A., & Heymsfield, S. B. (2009). F1000 Medicine Reports, 1, 59. https://doi.org/10.3410/M1-59

Willoughby, D., Hewlings, S., & Kalman, D. (2023). Current Opinion in Clinical Nutrition and Metabolic Care, 26(6), 521–528. https://doi.org/10.1097/MCO.0000000000000980

Cardio

A common question during a sprint is how to handle cardio.

The evidence-based answer is daily walking, with most other forms of cardio paused for the duration of the sprint.

This section explains the physiological reasoning.

What Exercise Does During Your Sprint

Your caloric deficit during a Fat Loss Sprint is typically 1,500–2,000 kcal/day. A moderate exercise session burns 100–400 kcal. In context: exercise is not the main driver of fat loss during a sprint — the diet creates the deficit. Exercise during your sprint is strategic rather than a meaningful source of calorie burn.

Physical activity during your sprint serves three purposes:

1. Increases your total daily energy expenditure, widening the deficit slightly
2. Maintains NEAT (non-exercise activity thermogenesis) by counteracting the subconscious movement reduction that happens during caloric restriction
3. Supports mood, sleep, and cognitive function during an already demanding phase

The type of activity matters here: low-intensity activity supports the sprint, while high-intensity activity can cost lean mass — the reasons follow.

Walking: The Recommended Cardio

Walking is the recommended cardiovascular activity during the Fat Loss Sprint. The recommendation is based on the physiology of severe caloric restriction, set out below.

Why Walking Works

It keeps you in the fat-burning zone. At low exercise intensities (roughly 40–65% of VO₂max, equivalent to brisk walking), your body derives the majority of its energy from fat oxidation. As intensity increases above this range, the fuel mix shifts toward carbohydrate (glycogen). Your glycogen stores are depleted during a Fat Loss Sprint. Demanding more carbohydrate fuel forces gluconeogenesis from amino acids, which means muscle protein gets broken down for energy (Romijn et al., 1993).

It doesn't compete with recovery from resistance training. Walking produces no meaningful muscle damage, does not deplete muscle glycogen, and does not elevate cortisol. Recovery resources are already limited during your sprint. Walking doesn't touch them.

It fights metabolic adaptation. One of the body's first responses to caloric restriction is a subconscious reduction in movement throughout the day, collectively called NEAT. Daily step targets directly counteract this. Walking during your sprint therefore does more than burn calories — it directly counteracts this adaptation.

It supports mood and focus. Caloric restriction puts pressure on mood, energy, and focus. Walking, particularly outdoors, is associated with improvements in all three (Oppezzo & Schwartz, 2014).

Your Daily Step Target

Leaner individuals have less fat mass to draw on and less recovery margin. If you are already lean going into this sprint, keep steps on the lower end and prioritize recovery.

Build gradually if you are currently sedentary. Starting at 4,000–5,000 steps and increasing each week is fine.

What to Avoid During Your Sprint

Running and High-Intensity Steady-State Cardio

Running, high-intensity cycling, rowing at tempo, and similar activities are not recommended during the sprint. The reasons are compounding:

• Glycogen demand is high. These activities rely heavily on glycogen for fuel. Without adequate glycogen, your body turns to gluconeogenesis from muscle protein, directly undermining the lean mass you are working to protect (Lemon & Mullin, 1980).
• Cortisol rises and stays elevated. Your sprint already mildly elevates cortisol due to the caloric deficit. Adding sustained high-intensity exercise compounds this. Chronic cortisol elevation accelerates muscle protein breakdown and promotes water retention (Tomiyama et al., 2010).
• Recovery is impaired. High-intensity cardio demands recovery resources that need to go to resistance training. You cannot adequately recover from both during a severe deficit.
• Injury risk increases. Caloric restriction reduces the body's capacity for tissue repair. Repetitive impact in an energy-depleted state raises the risk of overuse injuries.

HIIT

HIIT is not recommended for the same reasons, with additional concerns:

• HIIT intervals are almost entirely glycogen-dependent. Without glycogen, performance collapses and muscle catabolism fills the gap.
• The post-exercise "afterburn" (EPOC) attributed to HIIT — typically 50–80 kcal over 24 hours — does not justify the recovery cost during your sprint (LaForgia et al., 2006).
• The combination of HIIT and severe caloric restriction can suppress immune function (Walsh et al., 2011).

Group Fitness Classes, CrossFit, Spin

High-intensity group formats are not recommended for the same metabolic reasons: they are glycogen-dependent, cortisol-spiking, and recovery-intensive. The group setting also tends to encourage maximal effort, which is not advisable during severe restriction.

Why Exercise Choice Matters: The Energy Availability Framework

Energy availability (EA) measures how much energy is left for physiological function after accounting for exercise expenditure:

EA = (Energy Intake − Exercise Energy Expenditure) ÷ Fat-Free Mass

On a Fat Loss Sprint with approximately 850 kcal intake and 65 kg LBM:

EA below 30 kcal/kg FFM/day is associated with hormonal disruption. EA below 15 kcal/kg FFM/day produces severe metabolic consequences. Your sprint already operates at very low EA. High-intensity exercise pushes it toward dangerous levels (Loucks et al., 2011).

Walking keeps EA manageable. Running or HIIT doesn't.

Exercise: What's In, What's Out

Your Weekly Activity Structure

Use stairs, park further away, stand where you would otherwise sit. These small movements accumulate throughout the day and contribute meaningfully to your step count and NEAT.

Key Takeaways

• Walking is the recommended cardio during the sprint. It targets fat, protects muscle, and costs nothing in recovery.
• The protocol suggests 7,000–10,000 steps per day. Your in-app tracker marks the day's movement complete at ~7,000 steps (or the equivalent in light cardio); higher counts are a stretch goal.
• Running, HIIT, spin, CrossFit, and competitive sports are not recommended during the sprint. They rely on glycogen that is depleted during the sprint, raise cortisol, and impair recovery from resistance training.
• The sprint already operates at very low energy availability. High-intensity exercise pushes that into a physiologically difficult range.
• Resistance training (2–3x/week) plus daily walking is the protocol's recommended combination: metabolically sound, recovery-friendly, and sustainable for the full sprint.

References

Bryner, R. W., et al. (1999). Journal of the American College of Nutrition, 18(2), 115–121. https://doi.org/10.1080/07315724.1999.10718838

Hackney, A. C., & Walz, E. A. (2013). Trends in Sport Sciences, 20(4), 165–171. https://pubmed.ncbi.nlm.nih.gov/29882537/

LaForgia, J., Withers, R. T., & Gore, C. J. (2006). Journal of Sports Sciences, 24(12), 1247–1264. https://doi.org/10.1080/02640410600552064

Lemon, P. W. R., & Mullin, J. P. (1980). Journal of Applied Physiology, 48(4), 624–629. https://doi.org/10.1152/jappl.1980.48.4.624

Loucks, A. B., Kiens, B., & Wright, H. H. (2011). Journal of Sports Sciences, 29(S1), S7–S15. https://doi.org/10.1080/02640414.2011.588958

Oppezzo, M., & Schwartz, D. L. (2014). Journal of Experimental Psychology: Learning, Memory, and Cognition, 40(4), 1142–1152. https://doi.org/10.1037/a0036577

Romijn, J. A., et al. (1993). American Journal of Physiology-Endocrinology and Metabolism, 265(3), E380–E391. https://doi.org/10.1152/ajpendo.1993.265.3.E380

Tomiyama, A. J., et al. (2010). Psychosomatic Medicine, 72(4), 357–364. https://doi.org/10.1097/PSY.0b013e3181d9523c

Walsh, N. P., et al. (2011). Exercise Immunology Review, 17, 6–63. https://pubmed.ncbi.nlm.nih.gov/21446352/