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.

The purpose of this study was to compare one-repetition maximum (1-RM) and muscle activity in three chest-press exercises with different stability requirements (Smith machine, barbell, and dumbbells). Twelve healthy, resistance-trained males (age 22.7 ± 1.7 years, body mass 78.6 ± 7.6 kg, stature 1.80 ± 0.06 m) were tested for 1-RM of the three chest-press exercises in counterbalanced order with 3-5 days of rest between the exercises. One-repetition maximum and electromyographic activity of the pectoralis major, deltoid anterior, biceps, and triceps brachii were recorded in the exercises. The dumbbell load was 14% less than that for the Smith machine (P ≤ 0.001, effect size [ES] = 1.05) and 17% less than that for the barbell (P ≤ 0.001, ES = 1.11). The barbell load was ∼3% higher than that for the Smith machine (P = 0.016, ES = 0.18). Electrical activity in the pectoralis major and anterior deltoid did not differ during the lifts. Electrical activity in the biceps brachii increased with stability requirements (i.e. Smith machine

Multiple sclerosis (MS) patients suffer from impaired muscle activation and lower limb strength. Strength training enhances muscle activation and muscle strength, but neural adaptations to strength training remain unexplored in MS patients. The hypothesis was that maximal strength training (MST) using high loads and few repetitions would improve central neural drive and thus strength capacity of MS patients. 14 MS patients staying at a national MS rehabilitation center were randomly assigned to a MST group or a control group (CG). Both groups received "today's treatment". In addition, the MST group trained 4 x 4 repetitions of unilateral dynamic leg press and plantar flexion 5 days a week for 3 weeks. Neural adaptations of the soleus muscle were assessed by surface electromyography (EMG) activity, and by superimposed H-reflexes and V-waves obtained during maximum voluntary isometric plantar flexor contractions (MVCs). H-reflexes and V-waves were normalized by the M-wave (H(SUP)/M(SUP), V/M(SUP), respectively). In the MST group, MVC increased by 20 +/- 9% (P < 0.05). Soleus EMG activity and V/M(SUP) ratio increased by 40 and 55%, respectively, in the MST group compared to the CG (P