In strength and conditioning, we often hear vague talk about “movement systems” or “training the body as one piece.”
While that sounds good, there are only a few biological systems we can truly target, train, measure, and link to performance or rehab outcomes.
Let’s break down the Big 5 systems that deserve your attention, plus one wild card that shows up often but doesn’t deserve to lead your programming.
1. Muscular System
The workhorse of training.
We understand muscle better than any other tissue in the human body.
- What adapts: Hypertrophy, fiber type shifts, mitochondrial density, contractile force
- How to train it: Progressive resistance training (volume, load, etc.)
- Why it matters: Muscle generates force, protects joints, improves performance, and supports injury prevention and recovery.
- How we measure it: Strength tests, imaging (ultrasound, MRI), EMG, force plates
2. Tendon System
The force transmitter can be the limiting factor when athletes get stronger.
- What adapts: Stiffness, cross-sectional area, material strength (Young’s modulus), collagen turnover
- How to train it: Heavy slow resistance, isometrics, eccentrics, plyometrics
- Why it matters: Healthy tendons improve power transfer, reduce injury risk, and are central to rehab in load-related injuries.
- How we measure it: Ultrasound, stiffness testing, force-displacement relationships
3. Skeletal System (Bone)
The silent load-bearer that adapts to the mechanical environment.
- What adapts: Bone mineral density, geometry, structural strength
- How to train it: High-impact loading, resistance training, multi-directional movement
- Why it matters: Bone density supports resilience, especially in youth and aging populations. It's protective against injury and long-term disability.
- How we measure it: DXA, pQCT, CT imaging
4. Nervous System
The controller of performance that is fast, adaptive, and essential for skill and coordination.
- What adapts: Motor unit recruitment, rate coding, reflex timing, intermuscular coordination
- How to train it: Strength and power training, speed work, motor control drills, skill practice
- Why it matters: Neural drive explains early training gains, movement quality, and how athletes express strength or avoid injury.
- How we measure it: EMG, RFD, reaction time, movement precision
5. Cardiovascular System
The oxygen delivery network that fuels movement and recovery.
- What adapts: Heart size (eccentric hypertrophy), stroke volume, cardiac output, blood volume, capillary density, mitochondrial efficiency
- How to train it: Aerobic conditioning (steady-state or interval-based), tempo runs, repeated efforts, high-intensity intervals
- Why it matters: It delivers oxygen to working muscles, clears metabolic waste, supports endurance, and speeds recovery between reps, sets, and sessions.
- How we measure it: VO₂max, resting heart rate, time to recovery, lactate threshold, heart rate variability, and repeat sprint ability (RSA).
The Wild Card: Fascial System
Fascia is everywhere, but that doesn’t mean we can or should try to train it directly.
- What it does: Transmits force, stores elastic energy, connects muscle chains, supports proprioception.
- Why it's popular: The fascia hype cycle resurfaces every few years. Concepts like fascial slings, myofascial chains, and "tensegrity" sound appealing… but are often oversold.
- What we don’t know:
- How to directly measure fascial adaptation in humans
- How to isolate fascia-specific training effects
- Whether fascia-focused programs outperform conventional methods
Fascia indirectly responds to training.
When you strength train, do plyometrics, or stretch through full ranges, fascia is loaded and stimulated. You don’t need to "target" it for it to adapt.
Conclusion: Train What Matters Most
When it comes to improving performance, reducing injury risk, and building capacity, your focus should be on what’s:
⮕ Measurable
⮕ Adaptable
⮕ Backed by outcomes
The systems that check these boxes are:
- Muscle – drives force and movement
- Tendon – transmits and stores energy
- Bone – supports structure and resists load
- Nervous – coordinates everything
- Cardiovascular – delivers oxygen, clears waste, and fuels recovery
As fas as Fascia? It's part of the system and is a supporting actor but you do not need to prioritize it.
