Body composition and performance

Body composition and performance? When we hear the term body composition, most of us immediately think about how someone looks. We imagine abs, toned arms, or a “fit” silhouette. At best, we recognize that obesity is unhealthy or that carrying very high body weight can put strain on joints. But body composition goes much deeper than optics. At CrossFit Kreis 9, we see every day how body composition influences not just health but also performance — whether you’re running your first 5K, doing your first pull-up, or lifting heavy in the gym.

What body composition really means

Body composition describes what the body is made of, typically broken into two broad categories:

• Lean mass – muscle, bones, water, organs, connective tissue.
• Fat mass – both essential fat (needed for health and survival) and non-essential fat (extra storage).

Unlike body weight alone, which only tells us “how heavy,” body composition tells us what that weight consists of. Two people might weigh the same, but their capacity to run, lift, or even just feel energetic can be completely different depending on their ratio of lean to fat mass.

At CrossFit Kreis 9, we care about this ratio because it’s a far better indicator of performance and long-term health than the number on the scale.

Why body composition matters for performance

Performance is never only about training hours or talent. The composition of the body itself plays a huge role in how well it performs.

• Lean mass drives performance. Muscle is the body’s engine. It produces force, supports posture, absorbs impact, and even helps regulate metabolism. More lean mass usually means more potential for strength, speed, and endurance.
• Excess fat adds drag. While some fat is essential for health and recovery, too much acts like extra baggage. It doesn’t help you move faster or stronger, but it does increase the energy cost of movement. For sports where you carry your own bodyweight, like running, gymnastics, or CrossFit workouts, this can be a major limiter.
• Too little fat hurts recovery. On the other hand, being as lean as possible isn’t always best. Fat plays a role in hormone balance, immune function, and energy availability. Athletes who push body fat too low often see their performance and recovery suffer.

The key is not to chase extremes but to find the sweet spot — the body composition that allows for consistent, strong, sustainable performance.

Running and body composition

Nowhere is body composition more visible than in running. Runners come in all shapes and sizes, but the relationship between lean and fat mass plays a direct role in how efficiently they move.

• Distance running: Efficiency is everything. Carrying extra fat means carrying extra weight mile after mile, which increases the energy cost and slows pace. Elite marathoners tend to have very low body fat percentages and light frames with just enough lean muscle to support endurance. Their bodies are essentially optimized to carry as little “dead weight” as possible while sustaining powerful, repetitive motion.
• Sprint running: Sprinters, in contrast, rely heavily on lean muscle mass. They carry more muscle in the legs and glutes to generate explosive force, but still maintain low levels of fat to avoid unnecessary load. The balance is different than in marathon running, but the principle is the same — maximize lean tissue, minimize non-contributing tissue.

For many of our members at CrossFit Kreis 9 who also run, we often see that performance plateaus aren’t just about training volume. Improving body composition — either by adding lean mass in the right places or reducing unnecessary fat — often makes running feel smoother, faster, and more enjoyable.

Strength sports: mass moves mass

In the world of weightlifting, powerlifting, or strongman competitions, a different principle applies body composition and performance: mass moves mass.

Athletes in these sports rely on maximum force production. Since the body’s ability to build lean muscle is genetically and hormonally limited, many lifters intentionally carry extra fat in addition to muscle. The added body mass helps them lift heavier weights because it provides leverage, stability, and momentum — even if the fat itself doesn’t produce force.

That’s why you often see strongman competitors with massive frames, carrying both impressive muscle mass and significant fat. It’s not necessarily unhealthy in the short term; it’s a performance strategy. But many of these athletes reduce body fat once their competitive careers are over, because the additional fat no longer serves a purpose when the performance demands are gone.

In Olympic weightlifting, the concept plays out in weight classes. Lighter lifters need to be exceptionally lean to maximize their strength-to-bodyweight ratio. Heavier lifters in unlimited classes can afford — and often benefit from — carrying more total mass, even if it includes fat, because sheer bodyweight helps them stabilize and move massive loads.

At CrossFit Kreis 9, we don’t train for extreme specialization. Instead, we aim for balance: building enough lean mass for strength and resilience while keeping fat levels moderate so that running, gymnastics, and conditioning stay efficient.

The performance balance point

So what does this mean for the rest of us who aren’t elite athletes? It means that your ideal body composition is tied to what you want to do.

• If your goal is to run a faster 10K, losing non-essential fat may improve your efficiency more than adding training hours.
• If your goal is to lift heavier, building lean mass is essential — and carrying a bit of extra fat might not hold you back, depending on your sport.
• If your goal is overall fitness, longevity, and health, the balance lies somewhere in the middle: enough lean mass to stay strong, agile, and independent, with moderate fat to support recovery and hormone balance.

This is exactly what we help our members with at CrossFit Kreis 9: finding that individual balance that supports performance in workouts, but also in life outside the gym.

How to improve body composition for performance

• Strength training: Builds and maintains lean mass, which is critical for both runners and lifters.
• Conditioning work: Burns calories, improves efficiency, and supports fat management.
• Nutrition: Adequate protein, high-quality carbs, and controlled energy intake determine whether you gain muscle, lose fat, or both.
• Consistency: Extreme diets or training spikes rarely work. Long-term, steady habits reshape body composition in sustainable ways.

The takeaway for body composition and performance

Body composition is not just about how you look in the mirror. It’s about what your body is made of — and how that directly impacts performance. More muscle means more potential. Too much fat means more load. Too little fat means burnout.

At CrossFit Kreis 9, we believe in finding the body composition that works for you. Not for an ideal on Instagram, not for a competition standard, but for the goals you actually want to achieve. Whether that’s running smoother, lifting heavier, or simply staying fit for life, the right body composition is the foundation of performance.