Your muscles don’t make more protein faster when you lower weights slowly vs. lifting them up—so growth must come from rearranging what’s already there, not just making more.
Scientific Claim
Eccentric and concentric resistance training elicit similar long-term muscle protein synthesis rates in humans, suggesting that hypertrophy is not driven by differential anabolic signaling but possibly by structural reorganization of existing proteins.
Original Statement
“Phillips et al. reported similar increase in mixed protein synthesis... Cuthbertson et al. found no differences in myofibrillar FSR... Franchi et al. found no differences in myofibrillar FSR over 4 weeks... de novo sarcomere assembly in C2C12 myotubes can occur without the requirement for newly synthesized proteins.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design cannot support claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The claim uses 'similar' and 'suggesting' appropriately, as the evidence comes from multiple human studies measuring protein synthesis—no causal claim is made. The narrative review correctly frames this as an observed pattern, not a proven mechanism.
More Accurate Statement
“Eccentric and concentric resistance training are associated with similar long-term muscle protein synthesis rates in humans, suggesting that hypertrophy may be driven more by structural reorganization of existing proteins than by differential anabolic signaling.”
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.
Randomized Controlled TrialLevel 1bCausal equivalence of eccentric and concentric training on muscle protein synthesis over time in humans.
Causal equivalence of eccentric and concentric training on muscle protein synthesis over time in humans.
What This Would Prove
Causal equivalence of eccentric and concentric training on muscle protein synthesis over time in humans.
Ideal Study Design
A double-blind RCT with 30 healthy young men receiving deuterium oxide labeling for 4 weeks, randomized to either isolated eccentric (120% 1RM) or concentric (100% 1RM) leg extension training (3x/week). Primary outcome: myofibrillar fractional synthetic rate measured via mass spectrometry at baseline, week 2, and week 4, with muscle biopsies from vastus lateralis.
Limitation: Does not capture regional differences in synthesis or long-term (>6 month) adaptations.
Prospective Cohort StudyLevel 2bLong-term association between training mode and protein turnover patterns in trained individuals.
Long-term association between training mode and protein turnover patterns in trained individuals.
What This Would Prove
Long-term association between training mode and protein turnover patterns in trained individuals.
Ideal Study Design
A 1-year prospective cohort of 80 resistance-trained adults (20–40) who self-select eccentric- or concentric-dominant routines, with quarterly muscle biopsies and deuterium oxide labeling to measure myofibrillar and collagen protein synthesis rates, controlled for protein intake and training volume.
Limitation: Cannot control for unmeasured lifestyle or genetic confounders.
Cell Culture StudyLevel 5Whether mechanical stretch vs. shortening directly triggers sarcomere assembly without new protein synthesis.
Whether mechanical stretch vs. shortening directly triggers sarcomere assembly without new protein synthesis.
What This Would Prove
Whether mechanical stretch vs. shortening directly triggers sarcomere assembly without new protein synthesis.
Ideal Study Design
C2C12 myotubes subjected to controlled mechanical stretch (eccentric-mimetic) or shortening (concentric-mimetic) via flexible substrates, with and without protein synthesis inhibitors (cycloheximide), measuring sarcomere number via immunofluorescence and protein content via mass spectrometry over 72 hours.
Limitation: Cannot replicate in vivo muscle-tendon dynamics or systemic hormonal influences.
Evidence from Studies
Supporting (1)
Both types of weight training—pushing and lowering weights—make muscles grow about the same amount, even though they work differently inside the muscle. This suggests muscle growth isn’t just about chemical signals, but maybe about rearranging existing muscle parts.