When people who don't normally lift weights do a tough arm exercise twice, four weeks apart, their biceps don't stretch as much the second time, even though they're trying just as hard.
Scientific Claim
In untrained men, performing a second bout of maximal eccentric elbow flexor contractions 4 weeks after the first is associated with a 50% smaller increase in distal biceps brachii myotendinous junction displacement across 10 sets, suggesting reduced muscle lengthening during repetitive eccentric contractions.
Original Statement
“During ECC1, the displacement was significantly greater during sets 5 and 10 when compared with set 1, and for set 10 compared with set 5; however, no significant difference between the sets was evident during ECC2... In ECC1, the MTJ displacement doubled from set 1 to set 10 (16.4 ± 4.7 mm); however, there were no significant changes in ECC2 from set 1 to set 10 (9.3 ± 3.1 mm).”
Evidence Quality Assessment
Claim Status
overstated
Study Design Support
Design supports claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The study uses within-subject repeated measures but lacks randomization and blinding confirmation, preventing causal inference. The authors imply causation with 'mechanism underpinning,' but only association is supported.
Evidence from Studies
Supporting (1)
Reduced muscle lengthening during eccentric contractions as a mechanism underpinning the repeated-bout effect.
After doing hard arm exercises once, when the guys did them again four weeks later, their biceps didn’t stretch as much — meaning their muscles adapted and didn’t get stretched out as much during the workout, which helped them avoid damage.