The 3 invisible biological factors holding back your athletic performance

You train regularly, follow a structured plan, and yet you plateau. The reason is often not in your training programme but in your biological foundation. Ferritin, HbA1c, CRP: these three biomarkers can silently limit your progress, even in serious recreational and amateur athletes.

1. Ferritin and haemoglobin: your muscles' oxygen fuel supply

Two inseparable actors in oxygen transport to your muscles during exercise.

Why it matters: Oxygen is your muscles' primary fuel during exercise. It is carried by haemoglobin in red blood cells, itself dependent on ferritin, the body's iron reserve. When either is insufficient, your muscles receive less oxygen: reduced aerobic capacity, rapid breathlessness, and heavy legs.

Warning signs:

• Breathlessness disproportionate to your usual fitness level

• Performance stagnating or declining despite consistent training

• Chronic fatigue, pallor, brittle nails

• Difficulty maintaining intensity during longer efforts

Key takeaway: Ferritin below 30 ng/mL is associated with a significant drop in aerobic capacity, even without clinical anaemia. Get your levels checked before considering iron supplementation, and never supplement without a full prior blood panel.

2. HbA1c: a 3-month snapshot of your energy stability

Your ability to manage glucose determines your energy stability during training.

Why it matters: HbA1c reflects your average blood glucose over the past 3 months. If elevated, it signals poor glucose management: energy crashes during exercise, slower recovery, and greater dependence on carbohydrate intake to maintain intensity. Glycaemic instability also reduces metabolic flexibility, meaning the body's ability to alternate between glucose and fat as fuel sources.

Warning signs:

• Energy dips after meals or mid-afternoon

• A constant need for sugar during training

• Energy swings: peaks followed by crashes

• Difficulty sustaining long efforts without carbohydrate intake

Key takeaway: An HbA1c above 5.7% may reflect reduced insulin sensitivity, limiting glucose uptake by muscles and reducing performance on longer efforts.

3. CRP (C-reactive protein): the silent inflammation blocking your progress

Acute post-training inflammation is normal and necessary. Chronic inflammation is a brake on progress.

Why it matters: CRP is a marker of systemic inflammation. Training triggers acute inflammation that is necessary for muscular and cardiovascular adaptation. But if your CRP stays chronically elevated, your body is enduring training rather than absorbing it: fatigue accumulates, progress stalls, and injury risk rises.

Warning signs:

• Muscle soreness persisting beyond 48 to 72 hours

• Non-restorative sleep, waking during the night

• Irritability, loss of motivation

• A persistent feeling of being "drained", even after a rest day

Key takeaway: For cardio-metabolic prevention, the target is hs-CRP below 1 mg/L. Chronic inflammation can be amplified by insufficient sleep, a pro-inflammatory diet, chronic psychological stress, or training overload without adequate recovery.

These three biomarkers form an interconnected system: without optimal oxygen transport, glycaemic stability, and inflammation control, even the best training programme will struggle to produce lasting results.

At Lucis, we don't just tell you whether you're "within range": we analyse your biomarkers in full context, interpret the results, and provide a personalised plan adapted to your biological profile. Because lasting performance starts with understanding your body from the inside.

This article is based on our in-depth analysis of sports performance. To go further: Read the full article →

⚠️ The information in this article is provided for educational purposes only and does not constitute medical advice or a medical recommendation. Please consult a healthcare professional before modifying your diet, training, or supplementation.