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The purpose of this study was to compare hormonal, neuromuscular, and aerobic performance changes between a constant 2-minute interset recovery time and an interset recovery time based on individual heart rate (HR) responses during a 7-week (3 sessions per week, 3 × 10 repetition maximum [RM]) hypertrophic strength training period. The HR-dependent recovery time was determined with a Polar FT80 HR monitor, whereas the control groups used constant 2-minute periods between sets. From 24 male subjects who were divided in 2 equal groups, 21 completed the study (FT80, n = 12; CONTROL, n = 9). Serum blood samples analyzed for testosterone (TES) and cortisol (COR) were taken before and after the 7-week training period at rest. Concentric knee extension 1RM was measured before, after 4 weeks, and at the end of the training period. Concentric knee extension and knee flexion 10RM, central activation ratio (CAR), and maxVO2 were measured before and after the training. Serum TES concentrations were significantly higher after the training period in FT80 (p < 0.001), whereas no significant changes were observed in the CONTROL. Serum COR and maxVO2 were unchanged in both groups. In FT80 (p < 0.001), the increase in 10RM was higher (p < 0.05) than in CONTROL (p < 0.001). Central activation ratio increased in both groups, with the significant increase observed in FT80 (p < 0.05). The higher TES responses, 10RM, and CAR development in FT80 suggest that an HR-based recovery period system of the FT80 may be more efficient in this type of hypertrophic strength training (3 × 10RM). The protocol in this study may be considered as a metabolic training cycle that coaches and trainers can use within a longer periodized training program.

Experiments were carried out to determine whether the location of electrodes has an effect on eccentric exercise-induced changes in surface electromyography (sEMG) variables in the biceps brachii muscle. sEMG signals were recorded with a grid of 64 electrodes before and up to 4 days post-exercise. Root mean square (RMS) and mean power frequency (MNF) were calculated for: (1) each channel; (2) as an average of all channels; and (3) as an average of individual channel rows and columns. Mean muscle-fiber conduction velocity (CV) was estimated similarly but was based on double-differential channels. Maximal isometric voluntary torque decreased 21.3 +/- 5.6% post-exercise. The average sEMG variables decreased after the exercise and recovered 2 days (RMS and CV) or 4 days (MNF) post-exercise. Site-dependent changes were observed in sEMG variables. We conclude that site-dependent changes in sEMG variables after eccentric exercise can be detected and are influenced in part by anatomical factors.

Purpose: To test the association between exercise mode and the recovery pattern of baroreflex sensitivity (BRS) after exercise., Methods: The study population included healthy male subjects (N = 12, age: 31 +/- 3 yr). Four different interventions were performed in a randomized order: 1) aerobic exercise session on a bicycle ergometer, 2) light resistance exercise session, 3) heavy resistance exercise session, and 4) control intervention with no exercise. All interventions lasted 40 min. R-R intervals and continuous blood pressure were measured before (10 min) and 30-180 min after the interventions. BRSLF was calculated by the transfer function method from the low-frequency band (LF, 0.04-0.15 Hz) of the R-R intervals and systolic blood pressure spectra., Results: BRSLF had blunted until 30 min after aerobic and light resistance exercise (11.1 +/- 4.3 and 10.0 +/- 3.6 vs 17.5 +/- 7.0 ms.mm Hg(-1), P = 0.002 for both, compared with the control intervention, respectively). However, BRSLF was significantly blunted until 60 min after heavy resistance exercise (9.3 +/- 2.3 vs 15.1 +/- 4.7 ms.mm Hg(-1), P = 0.005, compared with the control intervention). The high-frequency power of R-R intervals (0.15-0.4 Hz) was significantly reduced, and the LF power of systolic blood pressure oscillation was significantly augmented 30 min after heavy resistance exercise (P < 0.01 for both), whereas both indices were restored to the control level by 30 min after aerobic and light resistance exercise., Conclusion: BRS after acute exercise is associated with exercise intensity, showing relatively rapid recovery after aerobic and light resistance exercise and delayed recovery after heavy resistance exercise. The delayed BRS pattern after heavy resistance exercise is regulated by delicate interplay between the withdrawal of vagal outflow and the probably increased sympathetic vasomotor tone documented by measurements of heart rate and blood pressure variability.

Introduction/purpose: Recovery of force and stretch reflex from exhaustive stretch-shortening cycle (SSC) exercise is usually bimodal, characterized as immediate exercise-induced performance reduction, with its quick recovery followed by a longer-lasting reduction in performance. A clear parallel exists between the respective changes in performance, neural activation, and metabolic or structural exercise-induced changes. This implies the existence of potential coupling between muscle failure and the induced neural adjustments that take place along its recovery. The present study was designed to explore the evidence of this coupling more thoroughly., Methods: H- and stretch reflexes were measured before and periodically after exhaustive SSC exercise in human subjects. Several markers of muscle damage and inflammation were also measured during the 8-d postexercise follow-up period., Results: The results indicate that acute changes of H- and stretch reflex patterns and maximal isometric force are associated with significant increases in lactate, interleukin 6, and prostaglandin E2 concentrations. The delayed changes in reflexes and isometric force occurred concomitantly with increases in muscle thickness, C reactive protein, and substance P concentrations and also in serum creatine kinase activity., Conclusion: The immediate postexercise decreases in H- and stretch reflexes are probably partially caused by activation of group III and IV afferent fibers by high lactate concentration in combination with possible increases in potassium outflow. Both of these parameters recovered quickly (i.e., 2 h after exercise). The events after the 2-h postexercise point are very likely to be related to muscle damage and associated inflammation. Group III and IV afferent fibers are probably reactivated during this period by mechanical factors.

The purpose of this study was to examine a course of force potentiation and/or inhibition during maximal voluntary eccentric action. Maximal voluntary force (MVC) of elbow flexion of ten healthy male volunteers was measured during isometric and isokinetic eccentric action starting from 80 degrees or 110 degrees and ending at 140 degrees elbow angle. Surface EMG was recorded from biceps brachii (BB) and brachioradialis (BR) muscles. Maximal voluntary eccentric force during the first 10 degrees of the movement was higher (P<0.001) than the maximal voluntary isometric preactivation force both in 80 degrees and in 110 degrees starting position at all three velocities (1, 2, and 4 rad s(-1)). The relative force potentiation was velocity dependent being smallest at the lowest stretching speed (P<0.01). Average EMG (aEMG) of BB and BR decreased as the joint angle increased both in eccentric and in isometric actions but the decrease in aEMG towards extension was somewhat higher in eccentric actions as compared to isometric. It was concluded that the force measured during the first 10 degrees of eccentric contraction always exceeded the maximal voluntary isometric preactivation force regardless of the joint angle or of the movement velocity. When maximal voluntary preactivation preceded the stretch, the relative force potentiation seemed to be greater at higher stretching velocities (velocity dependent) while at lower preactivation levels, the velocity dependence was not observed. Decreased muscle activation and lower maximal voluntary force towards the end of the movement suggested inhibition during maximal voluntary eccentric actions.

The purpose of this study was to examine acute hormonal and neuromuscular responses in men and women to 3 heavy resistance but clearly different exercise protocols: (a) submaximal heavy resistance exercise (SME), (b) maximal heavy resistance exercise (HRE), and (c) maximal explosive resistance exercise (EE). HRE included 5 sets of 10 repetition maximum (10RM) sit-ups, bench press, and bilateral leg extensions (David 210 machine) with a 2-minute recovery between the sets. In SME, the load was 70%, and in EE, the load was 40% from that used in HRE. A significant increase (p < 0.05) in serum growth hormone (GH) was observed after HRE both in men and women, but the increase was greater (p < 0.05) in men than in women. Serum testosterone (T) increased significantly (p < 0.05) only during HRE in men. Since GH and T are anabolic hormones, the acute exercise-induced response during HRE may play an important role in the long-term anabolic adaptation processes related to muscle hypertrophy and maximal strength development.

The EMG power spectrum may shift towards higher frequencies with higher movement velocities. Fatigue, on the other hand, can cause a decrease in the frequency components. The purpose of this study was to examine acute effects of explosive (EE) and heavy resistance (HRE) concentric leg press exercise on muscle force, EMG and blood lactate. The EE included five sets of ten repetitions with 40+/-6% of the isometric maximum at a 100 degrees knee angle performed as explosively as possible. The same number of repetitions was performed in HRE but with a heavier load (67+/-7% of the isometric maximum at a 100 degrees knee angle). Maximal isometric and single concentric actions of different loads, and an isometric fatigue test were measured before and after both exercises. Surface EMG was recorded from the vastus medialis muscles for analyses of average EMG (aEMG) and EMG power spectrum. Muscle fiber composition of the vastus lateralis was determined and blood lactate measured throughout the exercises. Mean power frequency and median frequency were higher during EE than during HRE (P<0.05). They increased during EE (P<0.05) as the exercise progressed, whereas during HRE no change or even slight decreases were observed. Signs of fatigue after pure concentric work were not observed after EE, and even after HRE, possibly due to the relatively small range of motion and short duration of action time, the fatigue was not that extensive. The relative number of fast twitch fibers was correlated (r=0.87, P<0.05) with the change in blood lactate in HRE. It was concluded that there may be a greater use of fast twitch motor units in explosive movements and that instead of fatigue, the present number of concentric actions in explosive exercise seems to have facilitated the neuromuscular system.

The purpose of this study was to examine acute neuromuscular fatigue and its recovery in men (n = 8) and women (n = 8). Two strenuous, but clearly different exercises were compared: maximal (MSL) versus explosive strength loading (ESL). The MSL included five sets of ten repetition maximum bilateral leg extensions. The same task and the same number of sets was performed in ESL but with 40% from the load used in MSL and performed as explosively as possible. Isometric force-time curves were measured during maximal voluntary bilateral isometric action of the leg extensors before the fatigue loading and after each set. The measurements were repeated after resting for 1 h, 2 h, 1 day and two days. Surface elecrtomyogram (EMG) activity was recorded from the vastus lateralis, vastus medialis and rectus femoris muscles. Blood samples from the fingertips were also taken throughout the experiment to determine blood lactate concentration. Marked changes took place in both sexes in force production during both MSL and ESL but the overall decreases were greater and the recovery was slower after MSL. Pronounced decreases occurred also in maximal integrated EMG (iEMG). In the men, the decrease in iEMG for the early contraction phase (0-100 ms) during ESL was greater (P < 0.05) than that of MSL, whereas the decrease in iEMG in the peak force phase (500-1500 ms) was similar. As expected, the increase in blood lactate concentration was greater during MSL in both sexes. It was concluded that heavy resistance loading may result in considerable acute fatigue of central and peripheral origin. The reduced electrical activity in the muscles accompanied by an accumulation of blood lactate led to marked decreases in strength. Explosive type loading, especially in men, appeared to lead primarily to central fatigue with less involvement of peripheral fatigue than MSL. The women seemed unable to fatigue themselves as much as the men, particularly in ESL.

The osteogenicity of a given exercise may be estimated by calculating an osteogenic index (OI) consisting of magnitude and rate of strain. Volleyball involves repetitive jumping and requires high power output and thus may be expected to be beneficial to bone and performance. The purpose of the present study was to examine if habitual volleyball playing is reflected in OI. Ten elderly habitual volleyball players [age 69.9 (SD 4.4) years] and ten matched controls volunteered [age 69.7 (4.2) years] as subjects. Distal tibia (d), tibial mid-shaft (50) and femoral neck (FN) bone characteristics were measured using pQCT and DXA. To estimate skeletal rigidity, cross-sectional area (ToA(50)), and compressive (BSI(d)) and bending strength indices (SSImax(50)) were calculated. Maximal performance was assessed with eccentric ankle plantar flexion, isometric leg press and countermovement jump (CMJ). A fast Fourier transform (FFT) was calculated from the acceleration of the center of mass during the CMJ. Maximal acceleration (MAG) and mean magnitude frequency (MMF) were selected to represent the constituents of OI. OI was calculated as the sum of the products of magnitudes and corresponding frequencies. Volleyball players had 7% larger ToA(50) and 37% higher power in CMJ, 15% higher MAG and 36% higher OI (P or= 0.646). In conclusion, habitual volleyball players may be differentiated from their matched peers by their dynamic jumping performance, and the differences are reflected in the magnitude but not rate of loading. [ABSTRACT FROM AUTHOR]

Muscle mass and strength have been shown to be important factors in bone strength. Low muscular force predisposes to falling especially among elderly. Regular exercise helps to prevent falls and resulting bone fractures. Better understanding of muscle function and its importance on bone properties may thus add information to fracture prevention. Therefore the purpose of this study was to examine the relationship between bone strength and muscular force production. Twenty-young men [24 (2) years] and 20 [24 (3) years] women served as subjects. Bone compressive (BSI(d)) and bending strength indices (50 Imax) were measured with peripheral quantitative computed tomography (pQCT) at tibial mid-shaft and at distal tibia. Ankle plantarflexor muscle volume (MV) was estimated from muscle thickness measured with ultrasonography. Neuromuscular performance was evaluated from the measurements of maximal ground reaction force (GRF) in bilateral jumping and of eccentric maximal voluntary ankle plantarflexor torque (MVC). Specific tension (ST) of the plantarflexors was calculated by dividing the MVC with the muscle volume. Activation level (AL) was measured with superimposed twitch method. Distal tibia BSI(d) and tibial mid-shaft 50 Imax correlated positively with GRF, MVC and MV in men (r = 0.45-0.67, P < 0.05). Tibial mid-shaft 50 Imax and neuromuscular performance variables were correlated in women (r = 0.46-0.59, P < 0.05), whereas no correlation was seen in distal tibia. In the regression analysis, MV and ST could explain 64% of the variance in tibial mid-shaft bone strength and 41% of the variation in distal tibia bone strength. The study emphasizes that tibial strength is related to maximal neuromuscular performance. In addition, tibial mid-shaft seems to be more dependent on the neuromuscular performance, than distal tibia. In young adults, the association between bone adaptation and neuromuscular performance seems to be moderate and also site and loading specific. [ABSTRACT FROM AUTHOR]

This study focused on the architectural changes in the muscle-tendon complex during the immediate and secondary (delayed) reductions of performance (bimodal recovery) caused by an exhaustive rebound type stretch-shortening cycle (SSC) exercise. The isometric plantar flexor torque during maximum voluntary contraction (MVC) was measured together with recording of electromyography (EMG) and ultrasonography from the soleus muscle before (BEF), after (AFT), 2 h (2H), 2 and 8 days (2D, 8D) after the SSC exercise (n=8). The performance variables (MVC torque and EMG activation) followed the bimodal recovery patterns. This was not the case in the changes of the fascicle length and muscle thickness. The relative torque changes in MVC correlated positively (R=0.78, P=0.02) to the corresponding averaged EMG changes between BEF and 2H (BEF-->2H); the significance disappeared in the comparison between 2H and 2D (2H-->2D), during which period MVC showed a secondary reduction. The relative torque changes in MVC showed no correlation with the changes in muscle thickness between BEF-2H. However, this correlation between 2H-2D was negative (R=-0.85, P<0.01). The fascicle shortening/average EMG ratio in MVC increased at 2H, and then decreased more at 2D than 2H (P<0.05). Thus, the secondary performance decline was not related to the corresponding EMG reduction but to the increased muscle thickness, which peaked at 2D. The results suggest clearly that the secondary decline in MVC could be related to the increase in muscle volume. [ABSTRACT FROM AUTHOR]