Meo sagte ich solle hochladen :)

How Endurance Adaptations Occur 
Part 1: The Role of Repeated Muscle Contractions

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The longer one rides, the more muscle contractions accumulate over time. These contractions create metabolic and mechanical signals in the body that trigger adaptations (see Figure 1) .

Figure 1. Exercise-induced signaling overview. Repeated muscle contractions (endurance exercise) generate Ca²⁺ spikes and energy stress (AMP/ATP changes), which activate kinases and transcription factors. This triggers mitochondrial biogenesis, fat oxidation, and capillary growth. Adapted from Higginson et al., 2006 .

When a muscle contracts, ATP is used and breaks down into ADP and AMP. ADP and AMP then activate the enzyme AMPK. AMPK signals the body to produce more mitochondria and to use fat more efficiently for energy. This is part of the body’s way to respond to repeated energy demand (see Figure 2) .

Figure 2. Endurance vs. resistance signaling pathways. Endurance exercise activates AMPK (red arrows), promoting PGC-1α and mitochondrial biogenesis. Resistance exercise activates Akt/mTOR (green arrows) for muscle growth. Adapted from Fowler et al., 2024 .

Another key part of muscle contraction is the release of calcium. Each contraction causes a calcium spike, and repeated contractions accumulate these spikes over time. Calcium indirectly activates CaMK, which in turn activates PGC-1α. PGC-1α is the master regulator of endurance adaptations (see Figure 3). It:
	1.	Increases mitochondrial content
	2.	Improves fat oxidation
	3.	Increases aerobic enzymes (e.g., citrate synthase, cytochrome c)
	4.	Promotes capillary growth
	5.	Shifts muscle fibers toward a more oxidative (endurance) type

Figure 3. Ca²⁺/CaMK/AMPK → PGC-1α signaling. Calcium spikes activate CaMK, while energy stress activates AMPK; both converge on PGC-1α, which drives mitochondrial biogenesis, oxidative enzymes, and capillary growth. Adapted from Mootha & Handschin, 2011  .

This is how repeated muscle contractions trigger PGC-1α via CaMK and AMPK. Over time, these processes improve endurance, allowing a cyclist to sustain higher speeds for longer periods (see Figure 4)  .

Figure 4. Integrated view of endurance adaptations. Repeated endurance exercise induces acute calcium spikes and energy stress, activating kinases (CaMK, AMPK) and transcription factors, which cumulatively increase mitochondria, oxidative enzymes, and capillaries. Adapted from Eibl et al., 2021.

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How Endurance Adaptations Occur Part 1: The Role of Repeated Muscle Contractions

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Meo sagte ich solle hochladen :)

How Endurance Adaptations Occur Part 1: The Role of Repeated Muscle Contractions

Team 2026

Blacked out like a Phantom 🥷

Not every ride is worth uploading but this one is

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