title: The influence of maximal isometric activity on twitch and H-reflex potentiation, and quadriceps femoris performance.
abstract: The possibility of post-activation potentiation (PAP), enhanced neuromuscular performance following prior contractile activity, has received considerable attention but with little assessment of physiological changes. Maximum twitch force and H-reflex amplitude can be used to quantify the effect of prior activity, and may account for any PAP. Quadriceps femoris maximum twitch force (twitch potentiation, TP), the EMG Hmax/Mmax ratio and associated twitch force ratio (reflex potentiation, RP), were measured for 18 min after a period of rest (CON condition) and a 10 s isometric maximal voluntary contraction (iMVC, EXP condition) in eight recreationally active males. In comparison to CON, the Hmax/Mmax ratio (electrical RP) was potentiated for 5-11 min after iMVC (P < 0.05), with the highest values recorded 5 min post (+42 +/- 27% compared to mean of CON). Relative twitch force at Hmax (mechanical RP) was potentiated from 5 to 9 min post (P < 0.05). TP was greatest 10 s after iMVC (+67 compared to CON), and remained elevated for 18 min (P < 0.05). Optimal conditions for PAP were arbitrarily decided to occur 5 min after iMVC (TP, ~+16%; electrical RP, +42%), and performance (isometric rate of force development and isokinetic torque at 4.19 rad s(-1)) was measured at this point after CON and EXP treatments. No measures of performance were improved with EXP (P = 0.26-0.91). Electrical and mechanical RP of the quadriceps femoris was demonstrated, but the clear RP and TP found to occur after a 10 s iMVC did not produce any performance benefit.
authors.affiliation: School of Sport and Exercise Sciences, Loughborough University, Loughborough, UK. j.p.folland@lboro.ac.uk
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Folland
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Wakamatsu
authors.forename: Marius S
authors.initials: MS
authors.lastname: Fimland
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D017774:Long-Term Potentiation / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D012146:Rest / Q000502:physiology