Acidogenicity and acid tolerance of Streptococcus oralis and Streptococcus mitis isolated from plaque of healthy and incipient caries teeth.

BACKGROUND: Non-mutans low pH oral streptococci are postulated to contribute to caries etiology. OBJECTIVE: This study was undertaken to investigate whether the acidogenicity and acid tolerance of clinical strains of Streptococcus oralis and Streptococcus mitis correlate with health or early-stage enamel caries. DESIGN: S. oralis and S. mitis were isolated from plaque samples taken from the occlusal surfaces of second molars sampled at two different visits 4 years apart. All sites were sound at Visit 1; subjects were segregated into one of three groups based on the status of the site at Visit 2 and caries elsewhere in the dentition. Strains of S. oralis and S. mitis were evaluated for acidogenicity and acid tolerance, and the results correlated with the clinical status of the sites from which they were isolated. Mutans streptococci (MS) isolated from the plaque samples were also quantified, and the presence or absence of growth on pH 5.5 media or on media selective for bifidobacteria was recorded. RESULTS: No significant positive correlations were found between the acidogenicity properties of the S. oralis and S. mitis clones and caries at either visit. Similar results were obtained for acid tolerance of S. oralis clones but were inconclusive for S. mitis clones. A statistically significant positive correlation between MS levels and caries (or future caries) was evident at both visits, but there were no statistical correlations with the growth on pH 5.5 media or media selective for bifidobacteria. CONCLUSIONS: The low pH potential likely varies considerably among oral streptococcal species and is least likely to be found among strains of S. mitis. Accordingly, the concept and constitution of 'low pH streptococci' may need to be re-evaluated.

Comparison of methods to quantify volume during resistance exercise.

The purpose of this investigation was to compare 4 different methods of calculating volume when comparing resistance exercise protocols of varying intensities. Ten Appalachian State University students experienced in resistance exercise completed 3 different resistance exercise protocols on different days using a randomized, crossover design, with 1 week of rest between each protocol. The protocols included 1) hypertrophy: 4 sets of 10 repetitions in the squat at 75% of a 1-repetition maximum (1RM) (90-second rest periods); 2) strength: 11 sets of 3 repetitions at 90% 1RM (5-minute rest periods); and 3) power: 8 sets of 6 repetitions of jump squats at 0% 1RM (3-minute rest periods). The volume of resistance exercise completed during each protocol was determined with 4 different methods: 1) volume load (VL) (repetitions [no.] x external load [kg]); 2) maximum dynamic strength volume load (MDSVL) (repetitions [no.] x [body mass--shank mass (kg) + external load (kg)]); 3) time under tension (TUT) (eccentric time +milliseconds] + concentric time +milliseconds]); and 4) total work (TW) (force [N] x displacement [m]). The volumes differed significantly (p , 0.05) between hypertrophy and strength in comparison with the power protocol when VL and MDSVL were used to determine the volume of resistance exercise completed. Furthermore, significant differences in TUT existed between all 3 resistance exercise protocols. The TW calculated was not significantly different between the 3 protocols. These data imply that each method examined results in substantially different values when comparing various resistance exercise protocols involving different levels of intensity.

Power-time, force-time, and velocity-time curve analysis of the countermovement jump: impact of training.

The purpose of this investigation was to examine the impact of training on the power-, force-, and velocity-time curves of the countermovement jump (CMJ) through both cross-sectional and longitudinal comparisons. The most novel aspect of this study was the analysis of these curves for the entire movement at a sampling frequency of 386-506 Hz averaged across 30 subjects. Thirty subjects, all men, participated in this investigation and included 12 athletes and 18 untrained men. Two major comparisons were conducted: 1) an acute, cross-sectional examination comparing experienced jumpers (jump height > 0.50 m; n = 12 men's athletes) with nonjumpers (jump height < 0.50 m; n = 14 untrained men), and 2) a longitudinal examination comparing performance before and after 12 weeks of power training (training group n = 10 untrained men; control group n = 8 untrained men). Data obtained from the baseline testing session of 14 subjects involved in the longitudinal study were used for the cross-sectional examination to represent the nonjumper group. The cross-sectional examination revealed significant (p

Acute hormonal and neuromuscular responses to hypertrophy, strength and power type resistance exercise.

The purpose of the current study was to determine the acute neuroendocrine response to hypertrophy (H), strength (S), and power (P) type resistance exercise (RE) equated for total volume. Ten male subjects completed three RE protocols and a rest day (R) using a randomized cross-over design. The protocols included (1) H: 4 sets of 10 repetitions in the squat at 75% of 1RM (90 s rest periods); (2) S: 11 sets of three repetitions at 90% of 1RM (5 min rest periods); and (3) P: 8 sets of 6 repetitions of jump squats at 0% of 1RM (3 min rest periods). Total testosterone (T), cortisol (C), and sex hormone binding globulin (SHBG) were determined prior to (PRE), immediately post (IP), 60 min post, 24 h post, and 48 h post exercise bout. Peak force, rate of force development, and muscle activity from the vastus medialis (VM) and biceps femoris (BF) were determined during a maximal isometric squat test. A unique pattern of response was observed in T, C, and SHBG for each RE protocol. The percent change in T, C, and SHBG from PRE to IP was significantly (p

Power-time, force-time, and velocity-time curve analysis during the jump squat: impact of load.

The purpose of this investigation was to examine the impact of load on the power-, force- and velocity-time curves during the jump squat. The analysis of these curves for the entire movement at a sampling frequency of 200-500 Hz averaged across 18 untrained male subjects is the most novel aspect of this study. Jump squat performance was assessed in a randomized fashion across five different external loads: 0, 20, 40, 60, and 80 kg (equivalent to 0 +/- 0, 18 +/- 4, 37 +/- 8, 55 +/- 12, 74 +/- 15% of 1RM, respectively). The 0-kg loading condition (i.e., body mass only) was the load that maximized peak power output, displaying a significantly (p

The effect of resistance exercise on humoral markers of oxidative stress.

UNLABELLED: Previous research attempts to identify an oxidative stress response to acute resistance exercise have yielded mixed results. Inconsistencies in the current literature base probably reflect study-to-study variance in resistance exercise protocols; where high volume and short recovery elicit the most identifiable oxidative stress response. PURPOSE: This study examined the effect of resistance exercise intensity on blood oxidative stress. METHODS: To elicit a blood oxidative stress, 10 subjects undertook two different back squat protocols: 1) a hypertrophy protocol of four sets, 10 repetitions with 90 s of rest at 75% one-repetition max (1RM); and 2) a strength protocol of 11 sets, three repetitions with 5 min of rest at 90% 1RM. The resistance exercise protocols were standardized for total volume and completed in a randomized crossover fashion with 1 wk between trials. Blood drawn before (PRE), immediately following exercise (IP), and 60 min following exercise (60POST) was analyzed for markers of oxidative stress and damage. RESULTS: In response to both hypertrophy and strength exercise protein carbonyls were significantly elevated IP and 60POST while plasma lipid hydroperoxides were not. Following the hypertrophy protocol, trolox equivalent antioxidant capacity was elevated IP while urate lower than baseline. At the 60POST time point plasma ferric reducing ability of plasma was elevated following the hypertrophy protocol. Based on protein carbonyl data, a similar oxidative stress was incurred following both hypertrophy and strength protocols. CONCLUSION: Normalization for time of blood draw following the two protocols indicates that the magnitude of blood oxidative protein damage was identical between the protocols. These findings demonstrate that both resistance exercise protocols elicited a blood oxidative stress in a time-dependent fashion.

Influence of preactivity and eccentric muscle activity on concentric performance during vertical jumping.

The purpose of this investigation was to observe the influence of increasing amounts of preactivity and eccentric muscle activity imposed by three different jump types on concentric vertical jumping performance. Sixteen athletes involved in jumping-related sports at Appalachian State University, which is a Division IA school, performed a static jump (SJ), counter-movement jump (CMJ), and drop jump (DJ). Force, power, velocity, and jump height were measured during each jump type. In addition, muscle activity was measured from two agonist muscles (vastus lateralis, vastus medialis) and one antagonist muscle (biceps femoris). Preactivity and eccentric phase muscle activity of the agonist muscles (average integrated electromyography) was significantly (p < or = 0.05) higher during the DJ (preactivity, 0.2 +/- 0.11 mV; eccentric phase, 1.00 +/- 0.36 mV) in comparison with the CMJ (preactivity, 0.11 +/- 0.10 mV; eccentric phase, 0.45 +/- 0.17 mV). Peak concentric force was highest during the DJ and was significantly different among all three jump types (SJ, CMJ, DJ). Maximal jump height was significantly higher during the DJ (0.41 +/- 0.05 m) and CMJ (0.40 +/- 0.06 m) compared with the SJ (0.37 +/- 0.07 m). However, no significant difference in jump height existed between the CMJ and DJ. A positive energy balance, as assessed by force-displacement curves during the eccentric and concentric phases, was observed during the CMJ, and a negative energy balance was observed during the DJ. The data from this investigation indicate that a significant increase in concentric vertical jump performance is associated with increased levels of preactivity and eccentric phase muscle activity (SJ to CMJ). However, higher eccentric loading (CMJ to DJ) leads to a negative energy balance during the eccentric phase, which may relate to a non-significant increase in vertical jump height, even with coincidental increases in peak concentric force. Practitioners may want to focus on improving eccentric phase muscle activity through the use of plyometrics to improve overall jumping performance in athletes.

Relationship between countermovement jump performance and multijoint isometric and dynamic tests of strength.

The purpose of this investigation was to determine the relationship between countermovement vertical jump (CMJ) performance and various methods used to assess isometric and dynamic multijoint strength. Twelve NCAA Division I-AA male football and track and field athletes (age, 19.83 +/- 1.40 years; height, 179.10 +/- 4.56 cm; mass, 90.08 +/- 14.81 kg; percentage of body fat, 11.85 +/- 5.47%) participated in 2 testing sessions. The first session involved 1 repetition maximum (1RM) (kg) testing in the squat and power clean. During the second session, peak force (N), relative peak force (N x kg(-1)), peak power (W), relative peak power (W x kg(-1)), peak velocity (m x s(-1)), and jump height (meters) in a CMJ, and peak force and rate of force development (RFD) (N x s(-1)) in a maximal isometric squat (ISO squat) and maximal isometric mid-thigh pull (ISO mid-thigh) were assessed. Significant correlations (P < or = 0.05) were found when comparing relative 1RMs (1RM/body mass), in both the squat and power clean, to relative CMJ peak power, CMJ peak velocity, and CMJ height. No significant correlations existed between the 4 measures of absolute strength, which did not account for body mass (squat 1RM, power clean 1RM, ISO squat peak force, and ISO mid-thigh peak force) when compared to CMJ peak velocity and CMJ height. In conclusion, multijoint dynamic tests of strength (squat 1RM and power clean 1RM), expressed relative to body mass, are most closely correlated with CMJ performance. These results suggest that increasing maximal strength relative to body mass can improve performance in explosive lower body movements. The squat and power clean, used in a concurrent strength and power training program, are recommended for optimizing lower body power.

Trunk muscle activity during stability ball and free weight exercises.

The purpose of this investigation was to compare trunk muscle activity during stability ball and free weight exercises. Nine resistance-trained men participated in one testing session in which squats (SQ) and deadlifts (DL) were completed with loads of approximately 50, 70, 90, and 100% of one-repetition maximum (1RM). Isometric contractions during 3 stability ball exercises (quadruped (QP), pelvic thrust (PT), ball back extension (BE)) were also completed. During all exercises, average integrated electromyography (IEMG) from the rectus abdominus (RA), external oblique (EO), longissimus (L1) and multifidus (L5) was collected and analyzed. Results demonstrate that when expressed relative to 100% DL 1RM, muscle activity was 19.5 +/- 14.8% for L1 and 30.2 +/- 19.3% for L5 during QP, 31.4 +/- 13.4% for L1 and 37.6 +/- 12.4% for L5 during PT, and 44.2 +/- 22.8% for L1 and 45.5 +/- 21.6% for L5 during BE. IEMG of L1 during SQ and DL at 90 and 100% 1RM, and relative muscle activity of L5 during SQ and DL at 100% 1RM was significantly greater (P < or = 0.05) than in the stability ball exercises. Furthermore, relative muscle activity of L1 during DL at 50 and 70% 1RM was significantly greater than in QP and PT. No significant differences were observed in RA and EO during any of the exercises. In conclusion, activity of the trunk muscles during SQs and DLs is greater or equal to that which is produced during the stability ball exercises. It appears that stability ball exercises may not provide a sufficient stimulus for increasing muscular strength or hypertrophy; consequently, the role of stability ball exercises in strength and conditioning programs is questioned. SQs and DLs are recommended for increasing strength and hypertrophy of the back extensors.

The influence of body mass on calculation of power during lower-body resistance exercises.

The objective of this investigation was to examine the influence of body mass in the calculation of power and the subsequent effect on the load-power relationship in the jump squat, squat, and power clean. Twelve Division I male athletes were evaluated on their performance across various intensities in all the 3 lifts. Power output was calculated using 3 separate techniques: (a) including the contribution of body mass in force output (IBM), (b) including the contribution of the mass of body less the mass of the shanks and feet in force output (IBMS), and (c) excluding the contribution of body mass in force output (EBM). Peak power, peak power relative to body mass, and peak force calculated using EBM were significantly (p < or = 0.05) lower than outputs calculated with IBM and IBMS. The load that maximized power output was unchanged between the 3 techniques in the jump squat (0% 1 repetition maximum [1RM]) and power clean (80% 1RM) but was shifted from 56% (IBM and IBMS) to 71% 1RM (EBM) in the squat. Across all 3 movements, the shape of the load-power curve was affected when derived via the EBM method as a result of the underrepresentation of power output at light loads. This was due to the majority of the load being neglected when the mass of the body was removed from the system mass used in the calculation of force. This study indicates that not only is the actual power output significantly lower when body mass is excluded from the force output of a lower body movement, but the load-power relationship is altered as well. Therefore, it is imperative that the mass of the individual being tested is incorporated into the calculation of force used to determine power output during lower-body movements.

Validation of power measurement techniques in dynamic lower body resistance exercises.

The objective of this study was to investigate the validity of power measurement techniques utilizing various kinematic and kinetic devices during the jump squat (JS), squat (S) and power clean (PC). Ten Division I male athletes were assessed for power output across various intensities: 0, 12, 27, 42, 56, 71, and 85% of one repetition maximum strength (1RM) in the JS and S and 30, 40, 50, 60, 70, 80, and 90% of 1RM in the PC. During the execution of each lift, six different data collection systems were utilized; (1) one linear position transducer (1-LPT); (2) one linear position transducer with the system mass representing the force (1-LPT+MASS); (3) two linear position transducers (2-LPT); (4) the force plate (FP); (5) one linear position transducer and a force plate (1-LPT+FP); (6) two linear position transducers and a force place (2-LPT+FP). Kinetic and kinematic variables calculated using the six methodologies were compared. Vertical power, force, and velocity differed significantly between 2-LPT+FP and 1-LPT, 1-LPT+MASS, 2-LPT, and FP methodologies across various intensities throughout the JS, S, and PC. These differences affected the load-power relationship and resulted in the transfer of the optimal load to a number of different intensities. This examination clearly indicates that data collection and analysis procedures influence the power output calculated as well as the load-power relationship of dynamic lower body movements.

Power versus strength-power jump squat training: influence on the load-power relationship.

PURPOSE: The purpose of this investigation was to compare the impact of power training and strength-power training on the load-power relationship in the jump squat. METHODS: Twenty-six recreationally trained male subjects were randomly assigned to either a power training group (P; N=10), a strength-power training group (SP; N=8), or a control group (C; N=8). The P group trained for 12 wk, performing seven sets of six jump squats with the optimal load for maximal power output (body mass only, no external load), whereas the SP group performed five sets of six jump squats with the optimal load for maximal power output (body mass only, no external load) and three sets of three squats with 90% of their one-repetition maximum (1RM). Work performed by the P and SP subjects was equivalent throughout the 12 wk of training. Peak power relative to body mass (PP), jump height (JH), peak force relative to body mass (PF), and peak velocity (PV) during the jump squat were examined across loads of body mass (BM) and 20, 40, 60, and 80 kg at week 0 (baseline) and after weeks 6 (midtest) and 12 (posttest). RESULTS: After training, the P group significantly increased PP at BM and 20 kg, whereas the SP group significantly increased PP output across all loading conditions. Similarly, jump height was significantly increased by the P group at the lighter loads (BM, 20 kg, and 40 kg) and by the SP group at all loads. Whereas significant improvements in maximal power output and jump height at BM were observed in both P and SP groups, no difference in maximal power output or maximal jump height existed between the training groups. CONCLUSION: Combined lower-body strength-power training is effective as power training for improving maximum jump height and maximum power output in the jump squat, and it is more effective than power training at producing all-around (i.e., from BM to 80 kg) improvements in the load-power relationship of the jump squat.

Mechanical efficiency during repetitive vertical jumping.

The purpose of this study was to compare mechanical efficiency between repeated static jumps (SJ), countermovement jumps (CMJ), drop jumps from 75% of maximum CMJ jump height (75DJ) and drop jumps from 125% of maximum CMJ height (125DJ). Subjects included eight jump-trained males. All subjects completed 30 continuous repetitions in the SJ, CMJ, 75DJ, and 125DJ. Oxygen consumption, peak force and center of mass displacement for each repetition during the four jumping patterns were measured. ME was calculated from a combination of force-time curves, displacement-time curves and lactate-corrected oxygen consumption values. In addition, muscle activity was recorded from the vastus medialis, vastus lateralis and biceps femoris using surface electromyography (EMG). 125DJ and 75DJ resulted in significantly (P < or = 0.05) greater ME in comparison to CMJ and SJ. CMJ resulted in significantly greater ME in comparison to SJ. In addition, braking phase muscle activity was significantly greater in 125DJ and 75DJ in comparison to CMJ. Negative work was significantly different between 125DJ, 75DJ and CMJ (125DJ > 75DJ > CMJ). There was a significant positive correlation (r = 0.68) between ME and negative work performed across 125DJ, 75DJ and CMJ. These findings suggest that stretch-shortening cycle movements, which include a strenuous braking phase combined with simultaneous high muscle activity, increase ME. This may be due to optimal muscle-tendon unit kinetics and usage of stored elastic energy.

Optimal loading for maximal power output during lower-body resistance exercises.

PURPOSE: The influence of various loads on power output in the jump squat (JS), squat (S), and power clean (PC) was examined to determine the load that maximizes power output in each lift. METHODS: Twelve Division I male athletes participated in four testing sessions. The first session involved performing one-repetition maximums (1RM) in the S and PC, followed by three randomized testing sessions involving either the JS, S, or PC. Peak force, velocity, and power were calculated across loads of 0, 12, 27, 42, 56, 71, and 85% of each subject's 1RM in the JS and S and at 10% intervals from 30 to 90% of each subject's 1RM in the PC. RESULTS: The optimal load for the JS was 0% of 1RM; absolute peak power was significantly lower from the optimal load at 42, 56, 71, and 85% of 1RM (P < or = 0.05), whereas peak power relative to body mass was significantly lower at 27% of 1RM in addition to 42, 56, 71, and 85% of 1RM. Peak power in the S was maximized at 56% of 1RM; however, power was not significantly different across the loading spectrum. The optimal load in the PC occurred at 80% of 1RM. Relative peak power at 80% of 1RM was significantly different from the 30 and 40% of 1RM. CONCLUSION: This investigation indicates that the optimal load for maximal power output occurs at various percentages of 1RM in the JS, S, and PC.