AMPK: The Energy Sensor That Decides How Your Muscle Adapts to Exercise

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How a single enzyme, activated with every muscle contraction, orchestrates mitochondrial respiration, glucose transport, fat oxidation, cellular recycling and, potentially, the aging of the whole organism.

Standfirst

Every training session triggers, within seconds, a molecular cascade whose starting point is almost always the same: AMPK (AMP-activated protein kinase), the enzyme that detects the fall in energy level within the muscle cell and redirects the whole of metabolism accordingly. This article retraces its molecular structure, its activating kinases, its role in mitochondrial biogenesis, glucose and lipid regulation, autophagy, its dialogue with mTOR and SIRT1, the comparison of eleven training modalities, a hybrid protocol decoded, the links with longevity, and the clinical populations that stand to benefit. The level of evidence, systematically specified, distinguishes preclinical data from human data.

Key messages

🟢 AMPK is the “fuel gauge” of the muscle cell: it switches on when ATP runs short, typically during effort, and triggers reactions to produce more of it and to save it.
AMPK is an αβγ heterotrimer of which only three complexes dominate in human muscle (α2β2γ1, α2β2γ3, α1β2γ1); its allosteric and covalent (Thr172) activation can increase its activity more than 1000-fold (Hardie, Ross & Hawley, 2012).
Intensity, more than duration, is the main determinant of AMPK activation, with the α2β2γ3 complex being strongly mobilized during intense effort (HIIT, sprint) (Kristensen et al., 2015).
AMPK drives mitochondrial biogenesis via PGC-1α, demonstrated in humans by a 54% rise in the nuclear abundance of PGC-1α after endurance exercise (Wright et al., 2010).
Contrary to the received view, AMPK is not the main driver of fat oxidation during exercise; its role is clearer in recovery (Kjøbsted et al., 2018).
AMPK maintains a molecular antagonism with mTOR that partly explains the endurance/strength “interference,” although recent data qualify its practical magnitude.
🟢 Beyond muscle, AMPK is linked to several mechanisms of aging, but most of the evidence comes from animals; in humans, it is the functional benefits of exercise that are demonstrated.
High-intensity training benefits a broad range of clinical populations (obesity, type 2 diabetes, metabolic syndrome, controlled hypertension, older adults), subject to specific precautions.

Introduction: why AMPK is the central energy sensor of muscle

Skeletal muscle has extremely variable energy needs, multiplied several hundredfold during an intense contraction, which requires a detection system able to assess in real time the gap between energy demand and supply: this is the role of AMPK, a heterotrimeric kinase conserved from yeast to humans, which responds to the rise in AMP/ATP and ADP/ATP ratios that follows contraction (Kjøbsted et al., 2018).

🟢 Picture ATP as the immediately available fuel of the muscle cell: during effort, it is converted into “residues” (AMP, ADP) faster than it can be regenerated. AMPK detects this accumulation and tells the cell “stop spending energy to build, priority to energy production”.

AMPK is not a binary switch, but an integrator of multiple signals (energy, calcium, glucose, oxygen, cellular damage) that adjusts gene expression and the trafficking of key proteins such as GLUT4.

Molecular structure and mechanisms of AMPK activation

A heterotrimer with variable geometry

AMPK exists as a heterotrimeric complex composed of a catalytic α subunit (isoforms α1 or α2) and two regulatory subunits, β (β1 or β2) and γ (γ1, γ2 or γ3), that is, theoretically twelve combinations (Hardie, 2007; Kjøbsted et al., 2018). The α subunit carries the kinase domain, active after reversible phosphorylation of a threonine at position 172 (Thr172). The β subunit serves as a scaffold between α and γ, with a glycogen-binding domain. The γ subunit is the true energy sensor, binding AMP, ADP and ATP directly on its Bateman domains (Bateman, 1997).

In human skeletal muscle, three combinations dominate: α2β2γ1 (65% of expression, 30% of basal activity), α2β2γ3 (20% of expression, <5% of basal activity) and α1β2γ1 (15% of expression, 65% of basal activity) (Kjøbsted et al., 2018), with the γ3 isoform being specific to skeletal muscle (white type IIb fibers), associated only with α2 and β2 (γ3 study, 2004).

🟢 There are several “versions” of AMPK in muscle. The α2β2γ3 version, specific to muscle, comes into play mainly during intense efforts.

These descriptive data (immunoprecipitation, muscle biopsies) are solid for molecular description but insufficient for causal conclusions about training.

Figure 1. Molecular activation of AMPK

From AMP to activation: allostery and covalent phosphorylation

Muscle contraction lowers the cellular energy charge, increasing the AMP/ATP and ADP/ATP ratios. AMPK activation proceeds in two complementary steps (Kjøbsted et al., 2018; Xiao et al., 2011): an allosteric activation (binding of AMP to the Bateman domains of the γ subunit, moderately stimulating kinase activity) and a covalent activation (this binding promotes the phosphorylation of Thr172 by upstream kinases and protects this site from dephosphorylation). The combined effect can increase AMPK activity more than 1000-fold (Hardie, Ross & Hawley, 2012). This “canonical” AMP/ADP-dependent mechanism coexists with more recently described “non-canonical” pathways, through which AMPK also senses glucose, glycogen, fatty acids, or lysosomal and DNA damage (Steinberg & Hardie, 2022).

In humans, AMPKα2 activation depends clearly on intensity (from 40-50% of VO2max), whereas AMPKα1 appears to be activated more above 100% of VO2max (Wojtaszewski et al., 2000; Chen et al., 2003). Chronic training attenuates the acute AMPK response to an identical submaximal exercise bout (McConell et al., 2005), data derived from human biopsies in often small samples (n = 6 to 12).

The upstream kinases: LKB1, CaMKKβ and TAK1

AMPK requires phosphorylation of its Thr172 by a third-party kinase; three main candidates have been identified, with very different levels of evidence.

LKB1, the constitutively active kinase

LKB1 (Liver Kinase B1), in complex with STRAD and MO25, is the main upstream kinase responsible for phosphorylating α2-containing AMPK complexes in response to muscle contraction (Sakamoto et al., 2005; Koh et al., 2006). Its discovery in 2004 marked a conceptual turning point: LKB1 is constitutively active at rest; it is the conformational change in AMPK induced by AMP/ADP that makes it a better substrate for LKB1, not the reverse (Sakamoto et al., 2004).

🟢 LKB1 is like a switch that is always “ready to turn on”: it is not LKB1 that changes, it is AMPK itself which, “deformed” by AMP, becomes easier to activate.

In mice, muscle-specific deletion of LKB1 abolishes AMPK activation and contraction-stimulated glucose uptake, with no equivalent model in humans (Koh et al., 2006; Thomson et al., 2007).

CaMKKβ, calcium-dependent activation

CaMKKβ constitutes an alternative pathway to LKB1, preferentially phosphorylating AMPKα1 during prolonged low-intensity exercise (Hawley et al., 2005; Woods et al., 2005): it responds to intracellular calcium, independently of energy status, with a quantitatively smaller role (Kjøbsted et al., 2018). Caffeine thus induces a calcium release that preferentially activates CaMKK-AMPKα1 in isolated rodent muscle (caffeine review, 2026), a preclinical level of evidence.

TAK1, a controversial upstream kinase

TAK1 (MAP3K7) has been proposed as a third direct upstream kinase of AMPK (Exp. Mol. Med. review, 2016), without established consensus (review, 2018). Its role is better documented as an autonomous regulator of muscle mass: in mice, its inactivation causes severe atrophy and an increase in AMPK phosphorylation (Hindi et al., 2018), exclusively preclinical evidence.

Box 1: How is AMPK activation measured?

In nearly all of the studies cited, AMPK activation is measured indirectly: Thr172 phosphorylation by western blot (the most frequent measurement), in vitro kinase activity, phosphorylation of downstream substrates (ACC), or transcriptional markers (PGC-1α and GLUT4 mRNA), which inform on functional consequences rather than on activation itself.

🟢 There is no simple method for measuring AMPK in an athlete outside the laboratory: for “functional” modalities (CrossFit, farmer’s carry, kettlebell), the reported levels remain estimates, not direct measurements.

Key messages: LKB1 is the dominant upstream kinase and is constitutively active (it is AMPK, modified by AMP, that becomes a better substrate, not LKB1 that becomes activated); CaMKKβ responds to calcium and preferentially activates AMPKα1; TAK1 remains controversial as an AMPK kinase. These mechanisms rest mostly on preclinical data.

AMPK and mitochondrial biogenesis: the pivotal role of PGC-1α

Its best-documented role in humans is the stimulation of mitochondrial biogenesis, through the control of PGC-1α and NRF1 (Jørgensen et al., 2007; Zong et al., 2002). AMPK directly phosphorylates PGC-1α, activating its own promoter and a multitude of mitochondrial genes (Jäger et al., 2007), a self-amplification loop demonstrated on specific residues (Thr177, Ser538).

🟢 PGC-1α is the “conductor” of the manufacture of new mitochondria. AMPK is the signal that switches it on when the muscle needs more long-term energy production capacity.

In humans, acute endurance exercise increases the nuclear abundance of PGC-1α by 54% in trained muscle, with an approximately five-fold rise in ACC phosphorylation (Wright et al., 2010), suggesting that AMPK, together with p38 MAPK, contributes to its nuclear translocation. PGC-1α undergoes dual post-translational regulation: phosphorylation by AMPK and acetylation/deacetylation by GCN5 (inhibitory) and SIRT1 (activating) (Lerin et al., 2006), with AMPK increasing the NAD⁺/NADH ratio and SIRT1 activity; its transcriptional coactivation also proceeds through NRF1, NRF2 and ERRα, leading to the activation of TFAM and to mitochondrial DNA replication (review, 2025), and it controls SIRT3 via ERRα (Brandauer et al., 2015).

Strong mechanistic evidence in mice, correlational in humans in small samples. Regular endurance training remains the main non-pharmacological lever of human mitochondrial biogenesis; HIIT and continuous endurance produce comparable effects at equivalent total work (Bartlett et al., 2012).

Key messages: AMPK directly phosphorylates PGC-1α, triggering a self-amplification loop demonstrated in humans (+54% after endurance exercise); this regulation combines phosphorylation (AMPK) and deacetylation (SIRT1); HIIT and continuous endurance produce comparable effects at equivalent total work.

AMPK, GLUT4 and glucose metabolism

AMPK also regulates glucose transport, at two levels: the acute translocation of GLUT4 to the plasma membrane, and the long-term transcription of its gene.

Acute translocation and transcriptional regulation

AMPK phosphorylates TBC1D1 and TBC1D4 (AS160), GAP proteins for the Rabs, whose inhibition allows GLUT4 vesicles to fuse with the plasma membrane (Chavez et al., 2008; Kjøbsted et al., 2016-2017). In mice, mutation of TBC1D1 at four AMPK sites reduces contraction-induced glucose uptake by approximately 35% (Vichaiwong et al., 2010); a more recent study specifies that uptake during exercise would not necessarily depend on AMPK, but that AMPKγ3 activity appears strongly correlated with uptake during post-exercise recovery (AMPKγ3 study, 2023), suggesting a role mainly in the replenishment of stores after effort.

AMPK also phosphorylates HDAC5, lifting the repression on MEF2 and increasing its binding to the GLUT4 promoter (McGee et al., 2008); an AICAR injection increases the expression of PGC-1α, hexokinase II and GLUT4 in wild-type mice but not in AMPKα2-deficient mice (Jørgensen et al., 2007), although acute exercise induces a similar GLUT4 gene response in both genotypes, suggesting mechanistic redundancy.

🟢 After a training session, your muscle becomes temporarily more sensitive to insulin and takes up blood glucose better, partly thanks to AMPK, an effect that accumulates with regularity.

Several studies show that AMPK is necessary for the increased insulin sensitivity after exercise, via TBC1D4 (Kjøbsted et al., 2017; Treebak et al., 2009): strong preclinical evidence for causality, observational in humans.

AMPK and fat oxidation: an important nuance

AMPK is classically presented as regulating fatty acid oxidation through the inhibitory phosphorylation of ACC2, which reduces malonyl-CoA production (an inhibitor of CPT1, the rate-limiting enzyme for fatty acid transport into the mitochondrion), theoretically facilitating fat oxidation. The recent literature strongly qualifies this model for exercise during effort: the ACC2 Ser212Ala mutation in mice prevents AICAR from increasing fat oxidation, but this phosphorylation does not play a significant role during contraction itself (O’Neill et al., 2014; O’Neill et al., 2015), and AMPK is likewise not essential for FAT/CD36 translocation during contraction ex vivo (Jeppesen et al., 2011).

🟢 The widespread idea that “AMPK makes you burn fat during exercise” is too simple: its role is in fact more pronounced after exercise, during recovery.

The regulation of fat oxidation by AMPK appears more relevant in post-exercise recovery, where the decrease in ACC and malonyl-CoA is associated with increased fatty acid oxidation (Rasmussen et al., 1998; Frøsig et al., 2009), evidence that is mostly preclinical (Kjøbsted et al., 2018). Nutritional timing during recovery could thus have a more decisive impact than intensity itself.

AMPK, autophagy and mitophagy: cellular housekeeping

It remains to be understood how AMPK is involved in the elimination of damaged cellular components, a process central to long-term muscle health.

Autophagy: the phosphorylation of ULK1

AMPK activates autophagy through the direct phosphorylation of ULK1 (the mammalian orthologue of Atg1) at several sites, in antagonism with mTORC1, which phosphorylates ULK1 at a distinct site to inhibit it under nutrient-rich conditions (AMPK/mTORC1 review, 2024); when AMPK is activated and mTORC1 inhibited, ULK1 initiates the formation of the autophagosome, the structure that sequesters the components to be recycled.

🟢 Autophagy is the cell’s cleaning service. AMPK is one of the main signals that trigger it when energy becomes scarce, as during physical exercise or fasting.

In mice, acute running causes mitochondrial oxidative stress (3-12h) followed by mitophagy (6h), preceded by an increase in the phosphorylation of AMPK-Thr172 and ULK1-Ser555 (Laker et al., 2017), a model called into question by a 2023 study suggesting that under acute energy stress AMPK would instead inhibit ULK1 (Nat. Commun., 2023; Autophagy, 2023): the field is undergoing full revision, with no direct human data.

Mitophagy: the PINK1/Parkin pathway

Mitophagy, the selective elimination of damaged mitochondria, is key to muscle mitochondrial quality, particularly with aging. The PINK1/Parkin pathway is the best characterized: PINK1 accumulates on depolarized mitochondria, recruiting Parkin, which ubiquitinates outer membrane proteins to target the organelle for degradation. The AMPK-mitophagy link goes through AMPK-ULK1, but also through the phosphorylation of MFF, which promotes the prior mitochondrial fission (Toyama et al., 2016, cited in Kjøbsted et al., 2018); AMPK acts upstream of PINK1 via ULK1, which phosphorylates Parkin within a few minutes, an early signal preceding PINK1 (30-60 min) (Front. Aging Neurosci., 2022). Muscle-specific AMPK knock-out mice show impaired mitophagy upon fasting and increased abnormalities with age (Laker et al., 2017).

The type of evidence is exclusively preclinical; the literature on the AMPK-PINK1/Parkin link in humans remains very limited.

Key messages: AMPK activates autophagy via ULK1, a mechanism under revision, with recent work suggesting an inhibitory role under acute stress; mitophagy (PINK1/Parkin) is regulated upstream by AMPK via ULK1 and MFF, with data almost exclusively preclinical.

The AMPK-mTOR-SIRT1 triangle: balancing catabolism and anabolism

Figure 2. AMPK–mTOR–PGC-1α–SIRT1 network

AMPK communicates with two other major cellular regulators: mTOR, the driver of growth and protein synthesis, and SIRT1, a NAD⁺-dependent deacetylase.

AMPK-mTOR: a two-way metabolic antagonism

AMPK and mTORC1 exert opposing effects: AMPK promotes ATP-producing catabolism, mTORC1 ATP-consuming anabolism. This antagonism operates through two direct mechanisms: phosphorylation of TSC2, which reduces the Rheb-GTP-dependent activation of mTORC1 (Inoki et al., cited in Cold Spring Harb. Perspect. Biol.), and direct phosphorylation of Raptor, which inhibits mTORC1 independently of TSC2 (Gwinn et al., 2008).

🟢 A company must choose between building (anabolism, mTOR) and conserving its resources during a shortage (catabolism, AMPK): these two “directions” inhibit each other.

This dual inhibition constitutes a “metabolic checkpoint” that halts cell growth in the event of an energy deficit. A 2020 discovery even shows the reverse: mTORC1 can directly inhibit AMPK (study, 2020).

The interference hypothesis of concurrent training

This antagonism is the origin of the “interference hypothesis”: endurance training could limit the hypertrophy/strength gains from resistance training when the two are combined. A landmark meta-analysis (Wilson et al., 2012, 21 studies) reports a reduction in strength gains of about 31%, in hypertrophy of about 12% and in power of about 18%, an effect that is more pronounced with endurance training ≥ 3 sessions/week, > 40 minutes, or involving running; a more recent meta-analysis qualifies this finding (Huiberts et al., 2024, 46 trials) with a more modest effect on hypertrophy (-0.23), smaller in men (-0.15) than in women (-0.31), and a greater resistance in trained subjects (Wilson et al., 2012; Huiberts et al., 2024).

More granular data further qualify the simple hypothesis: in trained men, after HIIT followed by rest and then a resistance exercise, AMPK-Thr172 phosphorylation triples, yet S6K1 nevertheless increases with no apparent inhibition of mTORC1, suggesting a tolerance in trained muscle (Apró et al., 2015, cited in a 2025 review); a 2021 study in endurance athletes likewise finds no acute molecular interference (Scientific Reports, 2021).

The molecular mechanism is at the preclinical level, strong and reproducible; the overall interference relies on high-level human meta-analyses. In practice: separate endurance and resistance training by several hours, limit the volume of concurrent endurance training (< 3 sessions/week, < 40 minutes) and favor cycling over running (Wilson et al., 2012).

AMPK-SIRT1: the role of NAD⁺

SIRT1 is a NAD⁺-dependent deacetylase coupled to AMPK through a crosstalk loop: the foundational study by Cantó et al. (2009) establishes that AMPK activation in muscle (metformin, fasting, exercise) increases the NAD⁺/NADH ratio, activating SIRT1, which then deacetylates PGC-1α (Cantó et al., 2009). AMPK triggers this deacetylation of PGC-1α and FOXO1; in AMPK-deficient mice, SIRT1 activation is impaired, confirming that AMPK precedes SIRT1 (Cantó et al., 2010), in part through the maintenance of NAMPT levels (Brandauer et al., 2013). A reciprocal loop also exists: SIRT1 can deacetylate LKB1, activating AMPK in return (Lan et al., 2008).

This loop is relevant to muscle aging: NAD⁺ levels decline with age and in mitochondrial myopathies (Gomes et al., 2013; Khan et al., 2014), motivating growing interest in NAD⁺ precursors (nicotinamide riboside, NMN), with human trials still at an early stage.

Key messages: AMPK inhibits mTORC1 through two direct mechanisms (TSC2, Raptor), creating a catabolism/anabolism checkpoint; concurrent training may reduce strength/hypertrophy gains, but the effect is more modest in recent meta-analyses and decreases in trained subjects; AMPK and SIRT1 form a NAD⁺-dependent crosstalk loop, relevant to muscle aging but with human evidence that remains limited.

Which training modality activates AMPK best? A comparison of eleven modalities

Which forms of training recruit this pathway most strongly? The literature is rich and robust for endurance training, HIIT and SIT, with direct measurements of AMPKα Thr172 phosphorylation in humans, but more limited for strength training, and virtually nonexistent for CrossFit, the farmer’s carry, the sled push, jump rope and kettlebell work: the levels reported in the table below for these modalities are therefore reasoned extrapolations, based on measured physiological data (VO2, HR, lactate, RPE) and on the dose-response relationships between intensity, glycogen depletion and AMPK activation.

The unifying principle: cellular energy charge as the signal

AMPK is activated when the local AMP/ATP (and ADP/ATP) ratio rises following ATP hydrolysis that exceeds the capacity for immediate resynthesis, which explains why intensity, and not duration alone, is the primary determinant of its activation, particularly in type II fibers (fast glycolytic), whose oxidative capacity is proportionally lower than that of type I fibers (Torma et al., 2019, Sports Med Health Sci.). Kristensen et al. (2015) illustrate this principle: Thr172 phosphorylation increases by 184% in type II fibers after HIIT, but not after work-matched continuous exercise of moderate intensity (Kristensen et al., 2015, J Physiol): the difference is not volume, but the instantaneous rate of ATP demand per fiber.

🟢 Ten minutes of intense sprinting recruits AMPK more than thirty minutes of walking, even at a similar total energy expenditure: it is the rate of energy consumption that matters most.

Table 1: comparison of AMPK activation by training modality

Figure 3. Comparison of training modalities and AMPK activation

Modality	Typical intensity	Typical duration	AMPK activation (Thr172)	PGC-1α activation	EPOC	Main adaptations
Continuous endurance (MICT)	50-75% VO2max, RPE 11-13	30-60 min	Moderate [D]	Moderate (mRNA ↑3.8×)	Low (~101-159 kJ)	Type I mitochondrial biogenesis, ↑VO2max
HIIT (e.g., 4×4 min)	80-95% VO2max, RPE 15-18	15-40 min	High [D] (↑184% type II, Kristensen et al., 2015)	High (increased nuclear abundance)	Moderate-to-high (~136-289 kJ)	Mitochondrial adaptations > work-matched continuous
Sprint Interval Training (SIT)	Supramaximal >100% VO2max, RPE 18-20	Sprints ≤30s ×4-8, 15-25 min	Very high [D]	High despite low volume	High (~241 kJ, the highest, Sousa et al., 2021)	Rapid mitochondrial gains despite low volume
Strength training (resistance)	65-85% 1RM, RPE 15-19/set	45-75 min	Moderate [D] (AMPKα2 ↑75%, Dreyer et al., 2006)	Low-to-moderate (transcripts unchanged at 12 wk, Porter et al., 2015)	Moderate-to-high	Mitochondrial complex I ↑2×, qualitative adaptation
CrossFit (mixed WOD)	HR 86-97% HRmax, RPE 17-19	4-23 min	High [E] HIIT/SIT analogy	High [E]	Likely high	Combined strength + cardio gains, weak evidence
Farmer’s carry (loaded carry)	Load 50-100%+ body weight	20-60s ×sets	Moderate-to-high [E]	Moderate [E]	Likely moderate	↑grip strength, trunk endurance
Sled Push	Load 50-125%+ body weight	10-40s ×sets	High [E]	High [E]	Likely high	↑sprint power/speed in the short term
Jump rope	57-92% VO2max, RPE 13-17	10-20 min	Moderate [E], between MICT and HIIT	Moderate [E]	Moderate (MET 10-12.5)	↑VO2max demonstrated after 8 weeks
Kettlebell (swings, complexes)	VO2 65-78% VO2max	10-20 min or Tabata	Moderate [E]	Moderate [E]	Moderate	↑VO2max over 4 weeks (snatch protocol)
Rowing (ergometer)	96-98% VO2max (2000m)	~6 min max, or intervals	High [E] SIT/HIIT analogy	High [E]	High (O2 debt ~13.4 L)	Among the highest VO2max values recorded (~67.6 mL/kg/min in elite athletes)
Assault Bike / Air Bike	Supramaximal, RPE 18-20 on sprints	Repeated 10-20s sprints	High [E] cycling SIT analogy	High [E]	Likely high	Maximal whole-body cardiovascular demand

[D] = direct human AMPK data for this modality; [E] = extrapolated by physiological analogy. Detailed sources in the reference list at the end of the article.

Why intense, repeated glycolytic efforts activate AMPK most strongly

Three converging features explain the superiority of HIIT, SIT and, by extrapolation, CrossFit over moderate continuous endurance training: a maximal rate of ATP depletion per unit of time during sprints or intervals at 90-95% VO2max (Torma et al., 2019), the preferential recruitment of type II fibers with a low oxidative capacity reserve, and the repetition of efforts with incomplete recovery, which partly explains the high EPOC. A second signal is added to these: muscle glycogen depletion, long assumed to involve direct binding of AMPK to glycogen, is called into question by a recent review showing the absence of this binding in vivo in rodents (Essays in Biochemistry, 2024): it coincides with, and amplifies, the rise in the AMP/ATP ratio, rather than activating it directly.

For hybrid modalities (farmer’s carry, sled push, kettlebell, jump rope), the absence of direct biopsies precludes a firm causal conclusion, but these exercises lie on a continuum between high-load resistance effort (PCr-dominant) and cyclic cardiometabolic effort; rowing and the assault bike, through their intensity close to VO2max and their whole-body engagement, share the metabolic profile of SIT/HIIT, an extrapolation that remains to be confirmed.

Key messages: AMPK activation follows a clear dose-intensity gradient (maximal for SIT, high for HIIT, moderate for strength training and hybrid modalities, moderate to low for continuous endurance training). The scarcity of biopsies for functional modalities calls for dedicated research.

Case study: the farmer’s carry + jump rope protocol decoded

Figure 4. Timeline of the farmer’s carry + jump rope protocol

Let us analyze a hybrid protocol representative of contemporary functional training: 45 seconds of farmer’s carry at 70 kg (approximately 35 kg per hand), immediately followed by 30 to 100 jump rope skips, then 2 minutes of recovery, repeated over 4 to 8 rounds. No published study has tested this exact combination: the analysis extrapolates from three distinct bodies of literature (biomechanics of loaded carries/strongman, jump rope physiology, intermittent exercise).

Muscle recruitment and limiting factor

EMG studies show, for the farmer’s carry phase, massive recruitment of the posterior chain and of the stabilizers, with ground reaction forces +240-247% higher than in unloaded walking (Keogh et al., Bond University) and extreme activation levels (latissimus dorsi 152% MVC) (Hybrid Pro Coach, citing PMC6901656). Grip remains the limiting factor, with grip strength decreases of 8.5 to 10.1% after repeated sets (Retos, 2025); for the rope, the triceps surae and the tibialis anterior are heavily recruited in repeated plyometrics (Children (MDPI), 2022).

🟢 In this type of exercise, it is generally your grip strength that gives out before your legs or your heart, as EMG data confirm.

Metabolic profile and expected activation of AMPK and mTOR

The Compendium of Physical Activities places strongman/loaded carry between 6 and 8 METs (Compendium 2024), and jump rope at 8.8-12.3 METs depending on cadence (2011 Compendium): for one round of the combined protocol, the reasonable estimate is 9 to 12 METs on average (31-42 mL/kg/min), an HR of 80-90% HRmax at the end of the rope phase (WKU thesis; PubMed) and a lactate peak of 8 to 14 mmol/L by analogy with strongman and intensive rope skipping (AUT thesis; PubMed).

Several mechanisms converge in favor of high AMPK activation: partial vascular occlusion and forearm hypoxia during the carry, phosphocreatine depletion, and a glycolytic intensity of the rope phase above the 60% VO2max threshold associated with AMPK activation (Hardie, 2009), a mechanistic inference and not a direct measurement. For mTOR, the sequence “heavy load then intense cardio” (the order followed here) preserves mTOR signaling better than the reverse order (Physiological Reports, 2020), although the AMPK activation of the rope phase may partially attenuate it.

Table 2: farmer’s carry + jump rope versus classic HIIT

Dimension	Farmer’s carry (45s/70kg) + Rope	Classic HIIT (30/30 or Norwegian 4×4)
Dominant energy system, phase 1	ATP-PCr then rapid glycolytic takeover	Glycolytic (30/30) or mixed (4×4)
Estimated VO2/MET	~9-12 METs (extrapolated)	4×4: close to VO2max at the end of the interval (90-95%)
Expected HR	70-90% HRmax, cumulative drift likely	4×4: 85-95% HRmax; 30/30: 80-90% HRmax
Peak blood lactate	~8-14 mmol/L (estimated)	30/30: 8-12 mmol/L; 4×4: 4-8 mmol/L
AMPK	Probably high (mechanical + metabolic stress + local hypoxia)	Well documented, robust, particularly with short intervals
mTOR	Significant activation in the loaded muscles; order favorable to maintaining the signal	Low to negligible (little heavy mechanical tension)
Strength/grip adaptations	Specific and substantial gain expected	Absent or minimal
VO2max adaptations	Moderate, probably lower than with dedicated HIIT	Solid and documented: +10-15% in 8-12 weeks (Norwegian 4×4 Guide)
Overall level of evidence	Low to moderate: extrapolation from adjacent literatures	High: very widely studied protocols

After 12 weeks, the most solid projections concern local muscular endurance (grip, calves, trunk) and a marked improvement in grip strength (large effect d = 0.99, The Sport Journal, 2025), while the improvement in VO2max remains modest. These projections combine disjointed literatures: no study has followed a cohort on this exact protocol, a major methodological limitation.

Key messages: this protocol combines heavy mechanical stress (carry) and cyclic glycolytic stress (rope), with grip as the documented limiting factor; the order “heavy load then cardio” favors maintenance of the mTOR signal while probably generating strong AMPK activation; no direct data exist on this exact protocol, all values being extrapolations to be interpreted with caution.

AMPK and longevity: beyond muscle

Figure 5. Integrative model of AMPK, exercise and longevity

AMPK has been proposed as a key regulator of “deregulated nutrient sensing”, one of the recognized “hallmarks of aging”, alongside mTOR, IGF-1/insulin and the sirtuins: its activation capacity declines with age in rodents, and its pharmacological or genetic activation extends lifespan in yeast, C. elegans and Drosophila (Physiology, 2011; Discoveries, 2015).

🟢 Essential nuance: nearly all of these data come from preclinical models (mice, C. elegans, Drosophila). In humans, it is the functional effect of exercise that is demonstrated, not AMPK as an isolated cause of slowed aging.

Inflammaging, oxidative stress and cardiovascular health

AMPK exerts an anti-inflammatory effect by inhibiting NF-κB, via SIRT1 and modulation of the NLRP3 inflammasome, counteracting “inflammaging” (PubMed, 2022). The loss of mitophagy with age feeds a vicious circle (damaged mitochondria, free radicals, pro-inflammatory pathways, additional suppression of PINK1/AMPK) (Front. Aging Neurosci., 2026), and it also regulates antioxidant defenses via the Bmal1/NRF2/ARE axis (Cells, 2022), evidence that is essentially mechanistic and preclinical. On the vascular side, activation of endothelial AMPK stimulates nitric oxide production via phosphorylation of eNOS (UWaterloo thesis, 2011); in rodents, its acute activation induces hypotension and vascular relaxation, accentuated in the hypertensive rat, and an experimental activator (O304) improves cardiac function in the aged mouse, partially mimicking exercise (Commun. Biol., 2021), evidence that is almost exclusively preclinical.

Type 2 diabetes, metabolic syndrome and neurodegeneration

AMPK is a pivotal target of glycemic control: its activation increases fatty acid oxidation, inhibits lipogenesis and suppresses hepatic glucose production independently of insulin (PubMed, 2009). Metformin activates it, probably through inhibition of mitochondrial Complex I, but independent mechanisms also contribute to its efficacy (PubMed, 2020); the MILES trial is testing whether it brings the transcriptomic profile of older subjects closer to that of young subjects (Discoveries, 2015), with no established equivalence to the benefits of exercise, which acts through multiple pathways that cannot be reproduced pharmacologically.

In the central nervous system, AMPK has an ambivalent role: its activation promotes autophagy and the clearance of misfolded proteins (amyloid, α-synuclein), but excessive activation may worsen neuronal atrophy depending on the context (J. Parkinson’s Dis., 2018). For Parkinson’s disease, the PINK1/Parkin/AMPK pathway is central: aging reduces Pink1 expression, favoring α-synuclein aggregation, whereas exercise upregulates PINK1-Parkin, PGC-1α and BDNF (Front. Aging Neurosci., 2026). For Alzheimer’s disease, experimental compounds such as magnolol improve amyloid pathology in preclinical models via the AMPK/mTOR/ULK1 axis (ScienceDirect, 2023), evidence that is almost exclusively preclinical; no advanced clinical trial demonstrates that an AMPK activator prevents these diseases in humans.

Sarcopenia

In aging muscle, AMPK has a dual role: it promotes mitochondrial biogenesis and the clearance of dysfunctional mitochondria, but it can also promote autophagic protein degradation, a balance whose net outcome on muscle mass remains uncertain (Age, 2013). In mice, the kinase DNA-PK, which is more active with age, inhibits muscle AMPK by blocking the chaperone HSP90α; its inhibition restores AMPK and protects against type 2 diabetes (Physiological Reviews, 2018). In humans, muscle AMPK activation depends strongly on intensity (the α2 isoform is activated only at high intensity) and does not interfere with hypertrophy in response to resistance training (Discoveries, 2015). Multiple meta-analyses of RCTs show that resistance training improves strength, gait speed and functional performance in sarcopenic older adults, with inconsistent effects on muscle mass itself (PubMed, 2021; Aging and Disease, 2020; J. Cachexia Sarcopenia Muscle, 2025), with an optimal dose of about 1220 MET-minutes/week identified for grip strength, and a minimum threshold of 600 MET-minutes/week for gait speed (PubMed, 2025).

Box 2: What we do not (yet) know about AMPK and longevity

The exact role of AMPK in autophagy is under revision (2023): it might inhibit, rather than activate, ULK1 during acute energy stress.
No large-scale human trial has demonstrated that a pharmacological activator (AICAR, O304) causally extends human lifespan.
The isolated contribution of AMPK, distinct from the other effects of exercise or metformin, remains difficult to establish in humans.
Ongoing trials (MILES) report surrogate biomarkers, not hard clinical endpoints (mortality, disease incidence).

Key messages: AMPK is linked to several “hallmarks of aging” (autophagy, mitophagy, inflammaging, oxidative stress, vascular health, neurodegeneration, sarcopenia), but mainly through preclinical models; direct human evidence remains very limited. What is demonstrated in humans are the functional benefits of exercise, AMPK being only one mediator among others; pharmacological activators, including metformin, are not validated equivalents of exercise.

Clinical applications: who should train to activate their AMPK?

Let us translate these mechanisms into concrete recommendations. AMPK activation by exercise promotes GLUT4 translocation, fatty acid oxidation, mitochondrial biogenesis and muscle autophagy, with mTORC1 inhibition as a corollary (Diabetes & Metabolism Journal, 2013). These mechanisms are insulin-independent, which makes them a particularly attractive therapeutic target in insulin-resistant states.

Obesity, type 2 diabetes and prediabetes

Obesity is accompanied by reduced muscle AMPK activity and by an accumulation of intramyocellular lipids that promotes insulin resistance; HIIT improves VO2max more (+1.83 mL/kg/min) and reduces fat mass more (-1.69%) than continuous training, with no difference in BMI (Obesity Science & Practice, 2017), high level of evidence. In patients with type 2 diabetes, muscle shows reduced basal AMPK; exercise activates the AMPK-TBC1D4 pathway, restoring an insulin-independent glucose uptake that is preserved despite the disease (Diabetes & Metabolism Journal, 2013), with HIIT being superior or equivalent for HbA1c and insulin sensitivity; microvascular complications (retinopathy, nephropathy, neuropathy) must be screened for before any intense prescription, since autonomic neuropathy impairs the chronotropic response (Postgraduate Medical Journal, 2013). In prediabetic individuals, intense exercise improves insulin sensitivity by approximately 50% from the very first sessions, independently of weight loss (ClinicalTrials.gov NCT05435196), moderate to high evidence for these three populations.

Hypertension and metabolic syndrome

AMPK activation improves endothelial function and nitric oxide bioavailability. A meta-analysis of 7 RCTs shows a modest reduction in systolic pressure with HIIT (-3.00 mmHg), of limited clinical relevance (PubMed, 2024). Severe uncontrolled hypertension (SBP ≥180 or DBP ≥110 mmHg) constitutes an absolute contraindication to HIIT and CrossFit until blood pressure is controlled (StatPearls, 2023). Metabolic syndrome (visceral adiposity, dyslipidemia, hyperglycemia, hypertension) is responsive to AMPK activation: a meta-analysis of 23 RCTs (1374 participants, Br J Sports Med 2024) shows that HIIT improves waist circumference (-4.12 cm), systolic pressure (-6.05 mmHg), diastolic pressure (-3.68 mmHg), HDL (+0.12 mmol/L), triglycerides (-0.34 mmol/L) and fasting glucose (-0.35 mmol/L), with effects comparable to MICT (British Journal of Sports Medicine, 2024): high level of evidence.

Stable heart failure

In heart failure, peripheral skeletal myopathy contributes to exercise intolerance; AMPK activation by HIIT stimulates muscle mitochondrial biogenesis. The SMARTEX-HF trial did not show superiority of HIIT over MICT for ventricular remodeling or peak VO2 (SMARTEX, Eur J Prev Cardiol.), whereas a more recent trial reports superiority of supervised HIIT (International Journal, 2024), moderate level of evidence with contrasting results. The rate of major events remains low with supervised HIIT (approximately 1/17,000 sessions, JAHA, 2018). HIIT in heart failure must be initiated exclusively in a supervised setting, after an exercise stress test and optimization of therapy, in accordance with the ESC recommendations (ESC Guidelines 2020).

Aging, older adults and strength athletes

Muscle AMPK activity declines with age, with an attenuated response to contraction, contributing to sarcopenia (Experimental Gerontology, 2014). Adapted HIIT improves VO2max and functional strength in older adults, often with better adherence and without excess adverse events when properly supervised; since the risk of falls is higher, cardiovascular screening and a frailty assessment are recommended before any intense prescription.

In strength athletes, adding metabolic work raises the question of AMPK-mTORC1 interference: a review of 42 studies indicates that a “strength then endurance” order, separated by more than 3 hours, limits acute molecular interference (Frontiers in Sports and Active Living, 2026). For CrossFit, one analysis reports benefits for body composition and a 35% reduction in injury risk when periodization is respected (EFSUPIT, 2025), but a review of more than 12,000 practitioners reports an injury prevalence of 35.3% (shoulder, spine, knee) (PubMed, 2022): certified supervision and progressive loading are indispensable to prevent rhabdomyolysis in beginners.

Table 3: summary of recommendations by population

Population	Recommended intensity	Weekly frequency	Key precautions
Obesity	85-95% HRmax (short intervals)	2-3 HIIT sessions + 2 resistance	CV screening if ≥2 risk factors
Type 2 diabetes	80-95% HRmax, intervals 30s-4min	3 sessions + 2 resistance	Screening for retinopathy/nephropathy/neuropathy; hypoglycemia risk
Prediabetes/insulin resistance	80-90% HRmax	3-4 sessions	Check overall CV risk
Hypertension	70-85% HRmax (controlled hypertension only)	3 sessions	Absolute contraindication if severe uncontrolled hypertension (≥180/110)
Metabolic syndrome	Short protocols (4×4 or 10×1 min)	2-3 sessions + resistance	Baseline cardiometabolic workup
Stable heart failure	85-95% peak HR, 4×4 min protocols	2-3 strictly supervised sessions	Cardiology consultation and exercise stress test mandatory
Older adults (sarcopenia, frailty)	70-85% HRmax or 60-80% 1RM	2-3 sessions	Frailty/fall assessment; supervision at the start of the program
Strength athletes	Predominantly glycolytic/short anaerobic	1-2 metabolic sessions, separated by >3h	Spacing to limit AMPK-mTOR interference
CrossFit practitioners	Variable depending on the WOD, planned periodization	3-4 sessions	Technical supervision, rhabdomyolysis prevention

Box 3: key safety message

For all populations at high cardiovascular risk, heart failure, severe uncontrolled hypertension or diabetes with micro/macrovascular complications, prior medical advice and a formal risk assessment are imperative before any prescription of HIIT, intense metabolic resistance training or CrossFit, with progressive initiation under qualified supervision and individualized adjustment.

Key messages: training that activates AMPK benefits a broad range of clinical populations, with high levels of evidence for obesity, type 2 diabetes and metabolic syndrome; precautions vary widely (absolute contraindication in severe uncontrolled hypertension, strict supervision in heart failure, systematic screening in diabetes). For strength athletes, spacing sessions apart (more than 3 hours) limits AMPK-mTOR interference without abolishing it.

Future directions

This synthesis highlights a paradox characteristic of exercise biology: the general mechanistic framework of AMPK (LKB1, CaMKKβ, inhibition of mTORC1, activation of PGC-1α and ULK1) rests on solid preclinical foundations, but many fine details (the exact role of TAK1, the link with PINK1/Parkin, the SIRT1-NAD⁺ loop, the role in autophagy under acute stress) remain established almost exclusively in animals. Four lines of research are priorities: human mechanistic studies combining biopsies and “-omics” approaches; direct metabolic validation for hybrid modalities (CrossFit, farmer’s carry, sled push, kettlebell, jump rope), whose growing popularity contrasts with the absence of dedicated biopsies; follow-up of ongoing trials on AMPK and longevity (MILES, metabolic syndrome), which will probably focus on surrogate biomarkers rather than hard clinical endpoints; and concurrent training trials stratified by training level and by sex.

🟢 Research on AMPK illustrates how science advances: a simple model (“burns fat”, “activates autophagy”, “extends life”) becomes more complex as data accumulate, revealing context-dependent nuances and a gap between mouse and human.

The development of non-invasive tools for measuring AMPK would be a major advance for sports medicine. In the meantime, structured exercise, combining resistance and aerobic work at moderate to high intensity, performed regularly and adapted to the individual risk profile, remains the only intervention supported by meta-analyses of human RCTs for benefits related to muscular and metabolic aging.

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