Michael J. Hartman

The relationship between vertical jump power estimates and weightlifting ability: a field-test approach.

&NA; Carlock, J.M., S.L. Smith, M.J. Hartman, R.T. Morris, D.A. Ciroslan, K.C. Pierce, R.U. Newton, E.A. Harman, W.A. Sands, and M.H. Stone. The relationship between vertical jump power estimates and weightlifting ability: A field‐test approach. J. Strength Cond. Res. 18(3):534–539. 2004.—The purpose of this study was to assess the usefulness of the vertical jump and estimated vertical‐jump power as a field test for weightlifting. Estimated PP output from the vertical jump was correlated with lifting ability among 64 USA national‐level weightlifters (junior and senior men and women). Vertical jump was measured using the Kinematic Measurement System, consisting of a switch mat interfaced with a laptop computer. Vertical jumps were measured using a hands‐on‐hips method. A counter‐movement vertical jump (CMJ) and a static vertical jump (SJ, 90° knee angle) were measured. Two trials were given for each condition. Testretest reliability for jump height was intra‐class correlation (ICC) = 0.98 (CMJ) and ICC = 0.96 (SJ). Athletes warmed up on their own for 2–3 minutes, followed by 2 practice jumps at each condition. Peak power (PP) was estimated using the equations developed by Sayers et al. (24). The athletes’ current lifting capabilities were assessed by a questionnaire, and USA national coaches checked the listed values. Differences between groups (i.e., men versus women, juniors versus resident lifters) were determined using t‐tests (p ≤ 0.05). Correlations were determined using Pearsons r. Results indicate that vertical jumping PP is strongly associated with weightlifting ability. Thus, these results indicate that PP derived from the vertical jump (CMJ or SJ) can be a valuable tool in assessing weightlifting performance.

The importance of isometric maximum strength and peak rate-of-force development in sprint cycling.

This study was designed to investigate the relationship of whole-body maximum strength to variables potentially associated with track sprint-cycling success. These variables included body composition, power measures, coachs rank, and sprint-cycling times. The study was carried out in 2 parts. The first part (n = 30) served as a pilot for the second part (n = 20). Subjects for both parts ranged from international-caliber sprint cyclists to local-level cyclists. Maximum strength was measured using an isometric midthigh pull (IPF). Explosive strength was measured as the peak rate-of-force development (IPRFD) from the isometric force-time curve. Peak power was estimated from countermovement (CMJPP) and static vertical jumps (SJPP) and measured by modified Wingate tests. Athletes were ranked by the U.S. national cycling coach (part 1). Sprint times (from a standing start) were measured using timing gates placed at 25, 82.5, 165, 247.5, and 330 m of an outdoor velodrome (part 2). Maximum strength (both absolute and body-mass corrected) and explosive strength were shown to be strongly correlated with jump and Wingate power. Additionally, maximum strength was strongly correlated with both coachs rank (parts 1 and 2) and sprint cycling times (part 2). The results suggest that larger, stronger sprint cyclists have an advantage in producing power and are generally faster sprint cyclists.

Do practical durations of stretching alter muscle strength? A dose-response study.

PURPOSE To examine the time course (immediate, 10, 20, and 30 min) for the acute effects of 2, 4, and 8 min of passive stretching (PS) on isometric peak torque (PT), percent voluntary activation (%VA), EMG amplitude, peak twitch torque (PTT), rate of twitch torque development (RTD), and range of motion (ROM) of the plantarflexors. METHODS Thirteen volunteers (mean +/- SD age, 22 +/- 3 yr) participated in four randomly ordered experimental trials: control (CON) with no stretching, 2 min (PS2), 4 min (PS4), and 8 min (PS8) of PS. Testing was conducted before (pre), immediately after (post), and at 10, 20, and 30 min poststretching. The PS trials involved varied repetitions of 30-s passive stretches, whereas the CON trial included 15 min of resting. PT, %VA, EMG amplitude, PTT, and RTD were assessed during the twitch interpolation technique, whereas ROM was quantified as the maximum tolerable angle of passive dorsiflexion. RESULTS PT decreased (P < or = 0.05) immediately after all conditions [CON (4%), PS2 (2%), PS4 (4%), and PS8 (6%)] but returned to baseline at 10, 20, and 30 min poststretching. %VA and EMG amplitude were unaltered (P > 0.05) after all conditions. PTT and RTD decreased (P < or = 0.05) immediately after the PS4 (7%) and the PS8 (6%) conditions only; however, these changes were not sufficient to alter voluntary force production. There were also increases (P < or = 0.05) in ROM after the PS2 (8%), the PS4 (14%), and the PS8 (13%) conditions that returned to baseline after 10 min. CONCLUSION Practical durations of stretching (2, 4, or 8 min) of the plantarflexors did not decrease isometric PT compared with the CON but caused temporary improvements in the ROM, thereby questioning the overall detrimental influence of PS on performance.

The Time Course of Musculotendinous Stiffness Responses Following Different Durations of Passive Stretching

STUDY DESIGN Repeated-measures experimental design. OBJECTIVE To examine the acute effects of different durations of passive stretching on the time course of musculotendinous stiffness (MTS) responses in the plantar flexor muscles. BACKGROUND Stretching is often implemented prior to exercise or athletic competition, with the intent to reduce the risk of injury via decreases in MTS. METHODS AND MEASURES Twelve subjects (mean +/- SD age, 24 +/- 3 years; stature, 169 +/- 12 cm; mass, 71 +/- 17 kg) participated in 4 randomly-ordered experimental trials: control with no stretching, 2 minutes (2min), 4 minutes (4min), and 8 minutes (8min) of passive stretching. The passive-stretching trials involved progressive repetitions of 30-second passive stretches, while the control trial involved 15 minutes of resting. MTS assessments were conducted before (prestretching), immediately after (poststretching), and at 10, 20, and 30 minutes poststretching on a Biodex System 3 isokinetic dynamometer. RESULTS MTS decreased (P<.05) immediately after all stretching conditions (2min, 4min, and 8min). However, MTS for the 2min condition returned to baseline within 10 minutes, whereas MTS after the 4min and 8min passive-stretching conditions returned to baseline within 20 minutes. CONCLUSIONS Practical durations of passive stretching resulted in significant decreases in MTS; however, these changes return to baseline levels within 10 to 20 minutes.

The effect of beta-alanine supplementation on neuromuscular fatigue in elderly (55–92 Years): a double-blind randomized study

BackgroundAgeing is associated with a significant reduction in skeletal muscle carnosine which has been linked with a reduction in the buffering capacity of muscle and in theory, may increase the rate of fatigue during exercise. Supplementing beta-alanine has been shown to significantly increase skeletal muscle carnosine. The purpose of this study, therefore, was to examine the effects of ninety days of beta-alanine supplementation on the physical working capacity at the fatigue threshold (PWCFT) in elderly men and women.MethodsUsing a double-blind placebo controlled design, twenty-six men (n = 9) and women (n = 17) (age ± SD = 72.8 ± 11.1 yrs) were randomly assigned to either beta-alanine (BA: 800 mg × 3 per day; n = 12; CarnoSyn™) or Placebo (PL; n = 14) group. Before (pre) and after (post) the supplementation period, participants performed a discontinuous cycle ergometry test to determine the PWCFT.ResultsSignificant increases in PWCFT (28.6%) from pre- to post-supplementation were found for the BA treatment group (p < 0.05), but no change was observed with PL treatment. These findings suggest that ninety days of BA supplementation may increase physical working capacity by delaying the onset of neuromuscular fatigue in elderly men and women.ConclusionWe suggest that BA supplementation, by improving intracellular pH control, improves muscle endurance in the elderly. This, we believe, could have importance in the prevention of falls, and the maintenance of health and independent living in elderly men and women.

Force-time curve characteristics and hormonal alterations during an eleven-week training period in elite women weightlifters.

The purpose of this investigation was to study the effects of an 11-week training period performed by female weightlifters. Two weeks before this investigation, baseline measures for total testosterone, cortisol, and testosterone:cortisol ratio were collected. The 11-week training program consisted of the core exercises (i.e., clean, clean and jerk, and snatch) and other supplemental exercises (i.e., clean pull, snatch pull, squat, and front squat). Hormonal, isometric, and dynamic middle thigh pull force-time curve characteristics were assessed biweekly throughout the duration of the investigation, whereas volume load and training intensity were assessed weekly throughout the investigation. The testosterone:cortisol ratio of the baseline (1.19 ± 0.64) was significantly different from the ratio of weeks 1 (0.67 ± 0.36) and 9 (0.94 ± 0.66). When the week-to-week values were compared, week 1 (0.67 ± 0.36) was significantly different (P < 0.05; &eegr;2 = 0.84) from week 3 (1.06 ± 0.54). A very strong correlation (r = −0.83; r2 = 0.69) was found between the percentage change of the testosterone:cortisol ratio and volume load from weeks 1 to 11. Moderate to very strong correlations were noted between the percentage change in volume load and isometric peak force, peak force during the 30% isometric peak force trial, and peak force during the 100-kg trial during the 11 weeks of training. The primary finding of this study was that alterations in training volume load can result in concomitant changes in the anabolic-to-catabolic balance, as indicated by the testosterone:cortisol ratio, and the ability to generate maximal forces.

Effects of Creatine Monohydrate and Polyethylene Glycosylated Creatine Supplementation on Muscular Strength, Endurance, and Power Output

Herda, TJ, Beck, TW, Ryan, ED, Smith, AE, Walter, AA, Hartman, MJ, Stout, JR, and Cramer, JT. Effects of creatine monohydrate and polyethylene glycosylated creatine supplementation on muscular strength, endurance, and power output. J Strength Cond Res 23(3): 818-826, 2009-The purpose of this study was to examine the effects of a moderate dose of creatine monohydrate (CM) and two smaller doses of polyethylene glycosylated (PEG) creatine on muscular strength, endurance, and power output. Fifty-eight healthy men (mean ± SD: age, 21 ± 2 years; height, 176 ± 6 cm; body mass [BM], 75 ± 14 kg) volunteered and were randomly assigned to 1 of 4 groups: (a) placebo (PL; 3.6 g of microcrystalline cellulose; n = 15), (b) CM (5 g of creatine; n = 13), (c) small-dose PEG creatine (1.25 g of creatine: PEG1.25; n = 14), or (d) moderate-dose PEG creatine (2.50 g of creatine: PEG2.50; n = 16). Testing was conducted before (pre-) and after (post-) a 30-day supplementation period. Measurements included body mass, countermovement vertical jump (CVJ) height, power output during the Wingate test (peak power [PP] and mean power [MP]), 1 repetition maximum bench press (1RMBP), 1RM leg press (1RMLP) strength, and repetitions to failure at 80% of the 1RM for bench press (REPBP) and leg press (REPLP). BM and MP (W) increased (p ≤ 0.05) from pre- to postsupplementation for the CM group only, whereas 1RMBP and 1RMLP increased (p ≤ 0.05) for the CM, PEG1.25, and PEG2.50 groups. CVJ height (cm and cm·kg−1), MP (W·kg−1), PP (W and W·kg−1), REPBP, and REPLP increased (p ≤ 0.05) for all groups. These findings indicated that the recommended safe dose of 5 g·d−1 of CM increased BM and improved muscle strength (1RMBP and 1RMLP). Smaller doses of PEG creatine (1.25 and 2.50 g·d−1) improved muscle strength (1RMBP and 1RMLP) to the same extent as 5 g·d−1 of CM, but did not alter BM, power output, or endurance. When compared to the PL group, neither CM nor PEG creatine supplementation improved peak power output (CVJ or PP), MP, or muscle endurance (REPBP or REPLP). Thus, PEG creatine may have ergogenic effects that are comparable to those of CM, but with a smaller dose of creatine.

Mechanomyographic amplitude and mean power frequency responses during isometric ramp vs. step muscle actions

The purpose of the present study was to compare the mechanomyographic amplitude (MMG(RMS)) and mean power frequency (MMG(MPF)) vs. torque relationships during isometric ramp and step muscle actions for the vastus lateralis (VL) and rectus femoris (RF) muscles. Nineteen subjects (mean+/-S.D. age=24+/-4 years) performed 2 isometric maximal voluntary contractions (MVCs) before and after 2 or 3 isometric ramp muscle actions from (5-95% MVC) to 9 submaximal step muscle actions (15, 25, 35, 45, 55, 65, 75, 85, and 95% MVC). MMG signals were recorded from the VL and RF muscles, and MMG(RMS) and MMG(MPF) values were computed for each corresponding percentage of the MVC. Absolute and normalized MMG(RMS) and MMG(MPF) vs. torque relationships were analyzed and interpreted on a subject-by-subject and composite pattern basis using polynomial regression and repeated measures ANOVAs. For MMG(RMS) and MMG(MPF), only 16-53% and 11-26% of the individual responses were consistent with the composite polynomial models, respectively. In addition, the normalized composite MMG(RMS) values were greater for the RF than the VL from 35 to 85% MVC. Only 47% of the MMG(RMS) and 5% of the MMG(MPF) individual patterns of responses were the same for the ramp and step muscle actions, and differences were also observed for the composite MMG(RMS) and MMG(MPF) patterns between the ramp and step muscle actions. Overall, these findings indicated that the torque-related patterns of responses for MMG(RMS) and MMG(MPF) were different among subjects (i.e., inter-individual variability) and were muscle- (VL vs. RF) and mode-specific (ramp vs. step).

Inter-individual variability in the torque-related patterns of responses for mechanomyographic amplitude and mean power frequency

The purpose of this study was to examine the inter-individual variability for the patterns of responses for mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus isometric torque in lower-strength (LS) and higher-strength (HS) individuals. Twelve participants (mean +/- S.D. age = 25 + 4 years) performed two isometric maximal voluntary contractions (MVCs) before and after completing nine submaximal step muscle actions (15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, and 95% MVC) of the right leg extensors. MMG signals were recorded from the vastus lateralis muscle, and MMG amplitude and MPF values were computed for each corresponding percentage of the MVC. Polynomial regression analyses indicated that the composite MMG amplitude versus isometric torque relationship was best fit with a linear model (r(2) = 0.980) for the LS group and a cubic model (r(2) = 0.994) for the HS group. The composite MMG MPF versus isometric torque relationships were best fit with linear models for both the LS (r(2) = 0.529) and HS (r(2)=0.591) groups. However, only 66% of the individuals exhibited the same linear MMG amplitude patterns as the composite relationship for the LS group, whereas only 33% of the individual relationships were cubic for the HS group. Only one subject exhibited a positive linear (r(2) = 0.681) relationship for the MMG(MPF) versus isometric torque relationship for either the LS or HS groups. These findings suggested that strength differences do not affect the patterns of responses for MMG amplitude or MPF. The lack of consistency between the individual and composite patterns of responses suggested some degree of inter-individual variability. Therefore, future studies should examine the individual patterns of response to draw conclusions about motor control strategies.

THE EFFECTS OF FATIGUE OF THE PLANTAR FLEXORS ON PEAK TORQUE AND VOLUNTARY ACTIVATION IN UNTRAINED AND RESISTANCE-TRAINED MEN

Hartman, MJ, Ryan, ED, Cramer, JT, and Bemben, MG. The effects of fatigue of the plantar flexors on peak torque and voluntary activation in untrained and resistance-trained men. J Strength Cond Res 25(2): 527-532, 2011-The purpose of this study was to compare the effects of fatigue of the plantar flexors on peak torque and voluntary activation in untrained (UT) and resistance-trained (RT) men. Six men with no previous resistance training experience and 8 men with similar histories of chronic resistance training (9.8 ± 5.9 years, 3.8 ± 0.7 days/week) volunteered for this study. Subjects performed isometric maximal voluntary contractions (MVCs) before and immediately after unilateral dynamic isotonic contractions performed at 40% of MVC until volitional exhaustion. Voluntary activation of the plantar flexors was assessed using the interpolated twitch method (ITT) and central activation ratio (CAR). Surface electromyographic (EMG) amplitude of the soleus and medial gastrocnemius (MG) was measured during the MVC. There were significant reductions in MVC torque in both UT and RT groups after the fatiguing exercise (−10.7 ± 6.8%, p < 0.02; −9.1 ± 8.7%, p < 0.02, respectively), with no difference in the number of repetitions performed between groups. The UT and RT men experienced a significant decrease in ITT after the fatiguing exercise bout (−14.2 ± 11.8%, p = 0.03; −7.8 ± 9.3%, p = 0.045, respectively). The UT group experienced a significant decrease in CAR (99.5 ± 0.8% to 91.4 ± 6.4%, p = 0.025) with no change (p > 0.05) in the RT group. There was also a fatigue-induced decrease in normalized EMG amplitude for the soleus and MG muscles in both groups (p < 0.05). However, no differences were determined between groups for ITT, CAR, or EMG. Despite similar reductions in MVC torque postexercise, the UT men had a significant decrease in CAR and experienced nearly twice the decline in ITT than the RT men. These results indicate that the neural adaptations associated with chronic resistance training may lead to less susceptibility to central fatigue as measured by ITT and CAR.