Postactivation potentiation enhances upper- and lower-body athletic performance in collegiate male and female athletes.

The purpose of this study was to determine the effect of postactivation potentiation (PAP)-inducing activities in 4 separate studies examining vertical (VJP) and horizontal (HJP) jump performance, shot put performance (SPP), and sprint performance (SP), in National Collegiate Athletic Association Division II athletes. Study 1: 12 male (mean ± SD; age = 20.2 ± 2.0 years; height = 178.1 ± 6.2 cm; weight = 73.3 ± 6.43 kg) and 8 female (age = 20.1 ± 1.0 years; height = 169.6 ± 5.5 cm; weight = 59.8 ± 7.6 kg) track athletes participated in HJP and VJP testing before and after performing a parallel back squat (PBS) at 85% 1 repetition maximum (RM). Study 2: 10 (6 men and 4 women) shot put throwers (age = 20.6 ± 0.7 years; height = 182.1 ± 9.8 cm; weight = 102.8 ± 23.6 kg) participated in SPP testing for control (C), 3RM bench press, and 3RM PBS protocols. Study 3: 7 football players (age = 20.4 ± 1.6 years; weight = 87.8 ± 8.3 kg; height = 184.3 ± 7.2 cm) participated in SP testing before (PBS1) and after (PBS2) performing a 3RM PBS. Study 4: 11 football players (age = 20.3 ± 1.8 years; height = 180.6 ± 7.5 cm; weight = 86.1 ± 12.8 kg) participated in VJP testing for C and 3RM PBS protocols. Results of study 1: There was a significant (p ≤ 0.05) increase in VJP (PRE = 61.9 ± 12.3 cm; POST = 63.6 ± 11.6 cm) and HJP (PRE = 93.7 ± 11.0 cm; POST = 95.9 ± 11.5 cm). Study 2: SPP after PBS (11.67 ± 1.92 m) was not different vs. C (11.77 ± 1.81), but bench press (11.91 ± 1.81 m) was significantly greater (p ≤ 0.05) than both PBS and C. Study 3: SP time was significantly lower for PBS2 (4.6014 ± 0.17995 seconds) vs. PB1 (4.6557 ± 0.19603 seconds). Study 4: There was no difference in VJP for C (68.35 ± 2.16 cm) vs. PBS (68.12 ± 2.51 cm). Our data show that a 3RM PBS resulted in significant improvements in VJP, HJP, SPP, and SP in National Collegiate Athletic Association Division II male and female athletes. Strength and conditioning practitioners should potentially alter their warm-up programs to include PAP protocols to enhance performance of power athletes. However, there were nonresponders in each study, and coaches and athletes need to determine whether it is worthwhile to identify nonresponders before implementing PAP protocols.

Effect of adiposity on insulin action after acute and chronic resistance exercise in non-diabetic women.

PURPOSE: Obesity may attenuate metabolic health improvements following lifestyle interventions. However, the effect of adiposity on insulin action following resistance exercise in young non-diabetic women is unknown. The purpose of this study was to test the hypothesis that adiposity attenuates improvements in insulin sensitivity and glucose-stimulated insulin secretion (INS0-60/GLC0-60) after both acute resistance exercise (ARE) and progressive training (PRT). METHODS: Twenty-six young non-diabetic women (21.2 ± 0.7 years) were randomly assigned to control (C; n = 7; BF 40.1 ± 2.1 %) or exercise groups: normal body fat (NBF; n = 8; BF 29.9 ± 2.3 %) and high body fat (HBF; n = 12; BF 48.2 ± 1.4 %). Acute whole-body exercises were performed at 60 % of 1-RM for three sets of 8-12 repetitions, and PRT was performed 3 days/week for 7 weeks. A 75 g OGTT was conducted before and after ARE and PRT to estimate insulin sensitivity (Matsuda index) and INS0-60/GLC0-60. Insulin area under the curve (AUC) was calculated using the trapezoidal model. RESULTS: ARE had no statistical effect on insulin action across groups. Strength and fat-free mass (via DXA) increased after PRT in both NBF and HBF (p < 0.05), but only HBF women decreased BF (p < 0.01). HBF women were less insulin sensitive at baseline compared to NBF women (p < 0.05). Insulin sensitivity increased 95 % and INS0-60/GLC0-60 decreased 32 % following PRT in NBF, but not HBF or C (p < 0.05). After training, enhanced insulin sensitivity was inversely related to decreased INS0-60/GLC0-60 (r = -0.71, p < 0.001), fasting insulin (r = -0.71, p < 0.001), and insulin AUC (r = -0.85, p < 0.001). CONCLUSION: Seven weeks of PRT increases insulin sensitivity and reduces glucose-stimulated insulin secretion in NBF, but not HBF women. Obesity attenuates exercise-induced improvements in glucose regulation in young non-diabetic women.

Interpreting normalized and nonnormalized data after acute static stretching in athletes and nonathletes.

The purpose of this study was to determine the effect of acute static stretching on torque and electromyography (EMG) in female athletes (ATHs) and nonathletes (NONATHs) using both normalized (NORM) and nonnormalized (NONNORM) data. Fifteen ATHs recruited from women's National Collegiate Athletic Association Division II varsity basketball and volleyball teams were paired to 14 NONATHs. Electromyography (microV) was detected over the rectus femoris during isokinetic leg extensions at 60 and 300 degrees .s before (PRE) and after (POST) static stretching. There was a significant main effect for torque (mean +/- SD PRE = 81.9 +/- 22.7 Nxm; POST = 77.0 +/- 21.9 Nxm) and EMG amplitude (PRE = 767.6 +/- 288.6 microV; POST = 664.2 +/- 219.3 microV) for PRE compared to POST. For the NORM data, there was a significant decrease in torque for the NONATHs (mean +/- SD PRE = 73 +/- 12 Nxm; POST = 67 +/- 12 Nxm) but no significant difference for the ATHs (mean +/- SD PRE = 65 +/- 11 Nxm; POST = 66 +/- 8 Nxm). The NONNORM data indicated that both the ATHs and NONATHs displayed a stretching-induced decrease in torque that may be manifested in a decreased ability to activate the muscle. The NORM data revealed the NONATHs but not the ATHs were hindered in their ability to produce torque as a result of the stretching. Coaches and ATHs may want to carefully consider whether to include stretching in their precompetition routine. When reading the literature, the practitioner should consider the manner in which the data were calculated and analyzed (NORM or NONNORM) because it may affect the conclusions of the study.

Effects of low- and high-volume stretching on bench press performance in collegiate football players.

The purpose of this study was to determine the effects of acute low- and high-volume static and proprioceptive neuromuscular facilitation (PNF) stretching on 1-repetition maximum (1RM) bench press. Fifteen healthy male National Collegiate Athletic Association Division II football players (age: 19.9 +/- 1.1 years; weight: 98.89 +/- 13.39 kg; height: 184.2 +/- 5.7 cm; body composition: 14.6 +/- 7.4%; and 1RM bench press: 129.7 +/- 3.3 kg) volunteered to participate in the study. Subjects completed 5 different stretching protocols integrated with a 1RM dynamic warm-up routine followed by 1RM testing in randomly assigned order. The protocols included (a) nonstretching (NS), (b) low-volume PNF stretching (LVPNFS), (c) high-volume PNF stretching (HVPNFS), (d) low-volume static stretching (LVSS), and (d) high-volume static stretching (HVSS). Two and 5 sets of stretching were completed for the low- and high-volume protocols, respectively. The stretching protocols targeted triceps and chest/shoulder muscle groups using 2 separate exercises. There were no significant differences in 1RM bench press performance (p > 0.05) among any of the stretching protocols NS (129.7 +/- 3.3 kg), LVPNFS (128.9 +/- 3.8 kg), HVPNFS (128.3 +/- 3.7 kg), LVSS (129.7 +/- 3.7 kg), and HVSS (128.2 +/- 3.7 kg). We conclude that low- and high-volume PNF and static stretching have no significant acute effect on 1RM bench press in resistance-trained collegiate football players. This suggests that resistance-trained athletes can include either (a) a dynamic warm-up with no stretching or (b) a dynamic warm-up in concert with low- or high-volume static or PNF flexibility exercises before maximal upper body isotonic resistance-training lifts, if adequate rest is allowed before performance.

Effect of mechanomyography as a biofeedback method to enhance muscle relaxation and performance.

The purpose of the study was to examine the potential for using the mechanomyographic (MMG) signal as a biofeedback method to enhance muscular relaxation and to improve performance during forearm flexion repetitions to fatigue. Twelve adult (mean +/- SD; age: 22.0 +/- 1.1 years) moderately trained subjects (weight: 82.3 +/- 29.2 kg; height: 165.7 +/- 49.0 cm) were instructed to relax the biceps brachii muscle using MMG biofeedback (BIO) provided by viewing a computer screen graphically displaying the MMG signal and then without using MMG biofeedback (NOBIO). Electromyographic (EMG) and MMG signals were detected midway over the biceps brachii during the relaxation protocol. In subsequent visits to the laboratory, subjects performed as many repetitions as possible at 85% of 1 repetition maximum with BIO and NOBIO using the seated preacher curl exercise. Two-way (biofeedback x gender) mixed factorial analyses of variance revealed significantly (p < 0.05) lower MMG (mean +/- SEM; BIO = 0.6 +/- 0.1 mV; NOBIO = 1.1 +/- 0.2 mV) and EMG amplitudes (BIO = 6.6 +/- 0.6 microV; NOBIO = 9.4 +/- 1.4 microV) for BIO when subjects were instructed to relax the biceps brachii muscle. There was no significant difference in the number of forearm flexion repetitions performed for BIO (mean +/- SD; 7.9 +/- 0.4 reps) vs. NOBIO (8.1 +/- 0.6 reps). The results of the present study revealed that using MMG as a biofeedback technique can enhance the development of muscle relaxation, but is not useful in delaying fatigue during forearm flexion repetitions. Our results may have been influenced by a relatively short training phase designed to teach subjects to use the MMG signal as a biofeedback method. Future studies are needed to determine whether MMG biofeedback can be used for other purposes. If MMG is found to be useful as a biofeedback method, it has some distinct practical advantages over EMG that the strength and conditioning athlete and professional may find appealing.

The effect of glycerol on torque, electromyography, and mechanomyography.

The purpose of this investigation was to determine the effect of hyperhydration on the electromyographic (EMG) and mechanomyographic (MMG) responses during isometric and isokinetic muscle actions of the biceps brachii. Eight (22.1 +/- 1.8 years, 79.5 +/- 22.8 kg) subjects were tested for maximal isometric, submaximal isometric, and maximal concentric isokinetic muscle strength in either a control (C) or hyperhydrated (H) state induced by glycerol ingestion while the EMG and MMG signals were recorded. Although fluid retention was significantly greater during the H protocol, the analyses indicated no change in torque, EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, or MMG MPF with hyperhydration. These results indicated that glycerol-induced fluid retention does not affect the torque-producing capabilities of a muscle, the impulses (EMG) going to a muscle, or muscular vibrations (MMG). It has been suggested that EMG and MMG can be used as direct electrical/mechanical monitoring, which could be presented to trainers and athletes; however, before determining the utility of these signals, the MMG and EMG responses should be examined under a variety of conditions such as in the present study.

Effect of static stretching of the biceps brachii on torque, electromyography, and mechanomyography during concentric isokinetic muscle actions.

The purpose of this study was to determine the effect of an acute static stretching bout of the biceps brachii on torque, electromyography (EMG), and mechanomyography (MMG) during concentric isokinetic muscle actions. Eighteen (men, n = 10; women, n = 8) adult subjects (M +/- SD age = 22.7 +/- 2.8 years; weight = 78.0 +/- 17.0 kg; height = 177.9 +/- 11.0 cm) performed maximal isokinetic (30 and 270 degrees.s(-1)) forearm flexion strength testing on 2 occasions while EMG and MMG were recorded. Subjects were randomly assigned to stretching (STR) or nonstretching (NSTR) protocols before strength testing. Two-way ANOVAs with repeated measures revealed significantly (p < or = 0.05) greater torque for NSTR (M +/- SEM = 36.9 +/- 3.3 N.m) vs. STR (35.2 +/- 3.3 N.m), significantly greater MMG amplitude for STR vs. NSTR for 30 degrees.s(-1) (STR = 93.5 +/- 14.4 mV; NSTR = 63.1 +/- 10.6 mV) and 270 degrees.s(-1) (STR = 207.6 +/- 35.6 mV; NSTR = 136.4 +/- 31.7 mV), and no difference in EMG amplitude. These results indicate that a greater ability to produce torque without prior stretching is related to the musculotendinous stiffness of the muscle rather than the number of motor units activated. This suggests that performing activities that reduce muscle stiffness (such as stretching), may be detrimental to performance.

Effect of moderate dehydration on torque, electromyography, and mechanomyography.

The purpose of the present investigation was to test the hypotheses that the mechanomyographic (MMG) signal would be affected by hydration status due to changes in the intra- and extracellular fluid content (which could affect the degree of fluid turbulence), changes in the filtering properties of the tissues between the MMG sensor and muscle, and changes in torque production that may accompany dehydration. Ten subjects (age 22.5 +/- 1.6 years) were tested for maximal isometric (MVC), submaximal isometric (25, 50, and 75%MVC), and maximal concentric isokinetic muscle strength of the biceps brachii in either a euhydrated or dehydrated state while the electromyographic (EMG) and MMG signals were recorded. Separate three-way and two-way ANOVAs indicated no change in torque, EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, and MMG MPF with dehydration. The lack of dehydration effect suggests that MMG may be more reflective of the intrinsic contractile processes of a muscle fiber (torque production) or the motor control mechanisms (reflected by the EMG) than the tissues and fluids surrounding the muscle fiber.

The relationships among peak torque, mean power output, mechanomyography, and electromyography in men and women during maximal, eccentric isokinetic muscle actions.

The purpose of the present investigation was to examine the velocity-related patterns of peak torque (PT), mean power output (MP), mechanomyographic (MMG) amplitude, and electromyographic (EMG) amplitude of the vastus lateralis (VL) muscle in men and women during maximal, eccentric isokinetic muscle actions of the leg extensors. Eight women [mean (SD)] [aged 23 (3) years] and seven men [aged 23 (2) years] volunteered for this investigation. Their PT was measured on a calibrated dynamometer at randomly ordered velocities of 30, 90, and 150 degrees x s(-1). A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes (Ag-AgCl) over the VL muscle. Their MP was determined using the dynamometer software. The results indicated no sex-related differences (P > 0.05) for the patterns of PT, MP, MMG amplitude, or EMG amplitude across velocity. The normalized values for MP and MMG amplitude increased (P<0.05) from 30 to 150 degrees x s(-1) (30 degrees x s(-1) <90 degrees x s(-1) < 150 degrees x s(-1)), while PT and EMG amplitudes remained unchanged across velocity. The results indicated close associations between the velocity-related patterns of MP and MMG amplitudes as well as PT and EMG amplitudes. Thus, MMG amplitude reflected the velocity-related changes in muscle power output, but not torque production, while EMG amplitude reflected torque production, but not muscle power output. During maximal, eccentric isokinetic muscle actions, EMG and MMG signals provided unique information regarding the electrical and mechanical aspects of muscle strength and power.