Jorge M. Zuniga

The Effects of Creatine Monohydrate Loading on Anaerobic Performance and One-Repetition Maximum Strength.

Abstract Zuniga, JM, Housh, TJ, Camic, CL, Hendrix, CR, Mielke, M, Johnson, GO, Housh, DJ, and Schmidt, RJ. The effects of creatine monohydrate loading on anaerobic performance and one-repetition maximum strength. J Strength Cond Res 26(6): 1651–1656, 2012—The purpose of this study was to examine the effects of 7 days of supplementation with 20 g·d−1 of creatine monohydrate (CM) on mean power (MP) and peak power (PP) from the Wingate anaerobic test (WAnT), body weight (BW), 1-repetition maximum (1RM) bilateral leg extension (LE) strength, and 1RM bench press (BP) strength. This study used a randomized, double-blind, placebo-controlled design. Twenty-two men (mean ± SD: age = 22.1 ± 2.0 years; height = 178.0 ± 5.8 cm; body weight [BW] = 77.6 ± 7.6 kg) were randomly assigned to either a supplement (SUPP; n = 10) or placebo (PLAC; n = 12) group. The SUPP group ingested 20 g·d−1 of CM powder for 7 days, whereas the PLAC ingested 20 g·d−1 of maltodextrin powder. Measurements for the PLAC and SUPP groups included BW, PP, and MP from two 30-second WAnTs (separated by 7 minutes), and 1RM strength for LE and BP. Testing was conducted before (PRE) and after (POST) 7 days of ingesting either the supplement or placebo. The results of this study indicated that there was a significant (p ⩽ 0.05) increase from PRE to POST testing in MP for the SUPP group (5.4%) but not for the PLAC group (−0.3%). There were no between-group differences, however, for 1RM LE and 1RM BP strength. Furthermore, there were no changes in PP or BW for either group. The findings of this study indicated that loading with 20 g·d−1 of CM for 7 days increased MP (5.4% increase) from the WAnT, but it had no effect on strength (1RM LE and 1RM BP), PP, or BW.

The effects of 4 weeks of an arginine-based supplement on the gas exchange threshold and peak oxygen uptake

The purpose of the present study was to examine the effects of the daily administration of an arginine-based supplement for 4 weeks on the gas exchange threshold (GET) and peak oxygen uptake. The study used a double-blind, placebo-controlled design. Forty-one college-aged males (mean age +/- SD = 22.1 +/- 2.4 years) were randomized into either the PLACEBO (n = 20) or ARGININE (n = 21) group. The placebo was microcrystalline cellulose. The ARGININE group ingested 3.0 g of arginine, 300 mg of grape seed extract, and 300 mg of polyethylene glycol. All subjects performed an incremental test to exhaustion on a cycle ergometer prior to supplementation (PRE) and after 4 weeks of supplementation (POST). The GET was determined by using the V-slope method of the carbon dioxide output vs. oxygen uptake relationship. The results indicated that there were significant mean increases (PRE to POST) in GET (4.1%), as well as in carbon dioxide output (4.3%) and power output (5.4%) at the GET for the ARGININE group, but no significant changes for the PLACEBO group (2.5%, 4.3%, and 3.9%, respectively). In addition, there were no significant changes in peak oxygen uptake for the ARGININE (-1.0%) or PLACEBO (-1.5%) groups. These findings supported the use of the arginine-based supplement for increasing GET and the associated power output, but not for increasing peak oxygen uptake during cycle ergometry.

The effects of skinfold thicknesses and innervation zone on the mechanomyographic signal during cycle ergometry

The purpose of this study was to examine the effects of skinfold (SF) thicknesses at four locations on the vastus lateralis (VL) muscle and the placement of accelerometers relative to the innervation zone (IZ) on the mechanomyographic (MMG) amplitude and mean power frequency (MPF) responses during incremental cycle ergometry. Twenty adults (age±SD=23.8±3.0 years) participated in the investigation. The MMG signals were detected during incremental cycle ergometry using four accelerometers placed on the right VL. Prior to the cycle ergometer test, SF thicknesses were measured. Simple linear regression analyses and one-way repeated measures analyses of variance (ANOVAs) were performed. The present study found that only 10% of the regression analyses and mean comparisons were significant (p<0.05). Furthermore, the accelerometer placed at the most proximal site (Prox 2) had significantly greater MMG amplitude and MMG MPF than accelerometers placed at more distal sites (Prox 1, Over IZ, and Dist). There were no significant differences, however, in SF thickness between accelerometer placement sites. In addition, the IZ had no effect on MMG amplitude and little effect on MMG MPF values. The results of the present study indicated that the SF thickness values and IZ did not affect the MMG signal.

Responses during exhaustive exercise at critical power determined from the 3-min all-out test

Abstract The purpose of the present study was to examine oxygen consumption rate ([Vdot] ), heart rate (HR), and ratings of perceived exertion (RPE) responses, as well as time to exhaustion (Tlim) values during continuous rides at critical power (CP) determined from the 3-min all-out test. Eighteen participants (mean ± s: 23.6 ± 3.5 years; 72.7 ± 18.2 kg) performed an incremental cycle ergometer test to exhaustion to determine peak oxygen consumption rate ([Vdot] peak) and HR peak. Critical power was determined from the 3-min all-out test. Metabolic responses ([Vdot] and heart rate), RPE, and Tlim were recorded during continuous rides to exhaustion at CP. Linear regression and t-tests were used to compare [Vdot] , heart rate, and RPE responses during the continuous rides to exhaustion. The Tlim at CP was 12.5 ± 6.5 min. There were significant increases in [Vdot] , HR, and RPE during the continuous rides at CP and 15 of the 18 participants reached [Vdot] peak at exhaustion. Therefore, the [Vdot] , heart rate, and RPE responses, as well as the Tlim values in the present study suggested that CP determined from the 3-min all-out test overestimated the “true” CP and was within the severe exercise intensity domain.

The influence of the muscle fiber pennation angle and innervation zone on the identification of neuromuscular fatigue during cycle ergometry

The purpose of the present investigation was to compare the electromyographic (EMG) responses and the estimated physical working capacity at the fatigue threshold (PWC(FT)) values recorded from electrode arrangements placed: (1) parallel to the muscle fiber pennation angle (MFPA), (2) parallel to the long axis of the femur, and (3) over the innervation zone (IZ) during incremental cycle ergometry. Thirteen college-aged males and females (mean age ± SD=22.4 ± 3.4 years) performed an incremental test to exhaustion on a cycle ergometer. A linear electrode array was utilized to determine the MFPA and location of the IZ of the vastus lateralis (VL). For determination of the PWC(FT) values, EMG signals were recorded from three bipolar electrode arrangements at different locations over the VL. The results of a one-way repeated measures ANOVA indicated there were no significant (p<0.05) mean differences in PWC(FT) values among the electrode arrangements (parallel to the MFPA=190 ± 36 W; parallel to the long axis of the femur=194 ± 40 W; and over the IZ=199 ± 51 W) or the EMG amplitude and MPF values at the common power outputs. There were also significant correlations (r=0.75-0.91) among the three electrode arrangements for PWC(FT) values. These findings suggested that the PWC(FT), like absolute EMG amplitude and MPF, is robust to the influence of electrode placement over the IZ as well as the orientation with respect to the MFPA during cycle ergometry.

A mechanomyographic frequency-based fatigue threshold test.

UNLABELLED Theoretically, the mechanomyographic (MMG) mean power frequency fatigue threshold (MMG MPF(FT)) describes the maximal isometric torque that can be maintained for an extended period of time with no change in the global firing rate of the unfused, activated motor units. PURPOSE The purposes of this study were twofold: (1) to determine if the mathematical model for estimating the electromyographic (EMG) MPF(FT) from the frequency of the EMG signal was applicable to the frequency domain of the MMG signal to estimate a new fatigue threshold called the MMG MPF(FT); and (2) to compare the mean torque levels derived from the MMG MPF(FT) test for the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles during isometric leg extension muscle actions. METHODS Nine adults (4 men and 5 women; mean+/-S.D. age=21.6+/-1.2 years) performed three or four continuous, fatiguing, isometric muscle actions of the leg extensors at 30, 45, 60, and 75% of maximum voluntary isometric contraction (MVIC) to exhaustion. Surface MMG signals were recorded from the VL, VM, and RF muscles during each fatiguing isometric muscle action. The MMG MPF(FT) was defined as the y-intercept of the isometric torque versus slope coefficient (MMG MPF versus time) plot. RESULTS There were no significant differences among the MMG MPF(FT) values for the VL, VM, and RF (34.8+/-23.4, 32.1+/-16.1, and 31.6+/-15.2 Nm, respectively) muscles. CONCLUSION The MMG MPF(FT) test may provide a non-invasive method to examine the effects of various interventions on the global motor unit firing rate during isometric muscle actions.

A mechanomyographic fatigue threshold test for cycling.

The purposes of this study were twofold: 1) to derive the mechanomyographic mean power frequency fatigue threshold (MMG MPFFT) for submaximal cycle ergometry; and 2) to compare the power outputs associated to the MMG MPFFT to other neuromuscular and gas exchange fatigue thresholds. 9 adults (5 men and 4 women; mean+/-SD age=23.7+/-3.7 years; body weight=66.3+/-8.2 kg) performed an incremental cycle ergometry test to exhaustion while expired gas samples, electromyographic (EMG), and MMG signals were measured from the vastus lateralis muscle. The non-significant correlations (r=0.17 to 0.66; p>0.05) among the physical working capacity at the fatigue threshold (PWCFT), MMG MPFFT, and gas exchange threshold (GET) suggested that different physiological mechanisms may underlie these 3 fatigue thresholds. A significant correlation (r=0.83) for the MPFFT vs. respiratory compensation point (RCP) suggested that these fatigue thresholds may be mediated by a common physiological mechanism. In addition, the significantly lower mean values found for the PWCFT (mean+/-SD=163+/-43 W), MMG MPFFT (132+/-33 W), and GET (144+/-28 W) than MPFFT (196+/-53 W) and RCP (202+/-41 W) suggested that these gas exchange and neuromuscular fatigue thresholds may demarcate different exercise intensity domains.

An open source 3D-printed transitional hand prosthesis for children

Introduction Advancements in computer-aided design programs, additive manufacturing, and open-source image editing software offer the possibility of designing, printing, and fitting transitional prosthetic hands and other prosthetic devices at very low cost. The development and use of 3D-printed transitional prosthetic devices to increase range of motion (ROM), strength, and other relevant variables would have a significant clinical impact for children with upper-limb deficiencies. Thus, the purpose of this study was to identify anthropometric, active ROM, and strength changes after 6 months of using a wrist-driven 3D-printed transitional prosthetic hand for children with upper-limb deficiencies. Materials and Methods Anthropometric, active ROM, and strength measurements were assessed before and after 6 months of using a 3D-printed transitional hand prosthesis. Five children (two girls and three boys, 3–10 years of age) with absent digits (one traumatic and four congenital) participated in this study and were fitted with a 3D-printed transitional hand prosthesis. Results There were significant hand × time interactions for the forearm circumference (p = 0.02), active ROM for flexion (p = 0.02), and extension values (p = 0.04). There were no significant hand × time interactions, however, for wrist flexion strength (p = 0.29), wrist extension strength (p = 0.84), active ROM for ulnar deviation (p = 0.5), active ROM for radial deviation (p = 0.25), and forearm skinfold values (p = 0.11). Conclusion Although durability, environment, and lack of printing standards for the manufacturing of 3D-printed prostheses are factors to consider when using these types of devices, the practicality and cost-effectiveness represent a promising new option for clinicians and those patients with upper-limb deficiencies living in developing countries. Thus, the Cyborg Beast transitional prosthetic hand represents a low-cost prosthetic solution for those in need of a transitional device to increase ROM and forearm circumference.

The effects of accelerometer placement on mechanomyographic amplitude and mean power frequency during cycle ergometry

The purposes of this study were threefold: (1) to compare the power output related patterns of absolute and normalized MMG amplitude and MPF responses for proximal and distal accelerometer placements on the vastus lateralis (VL) muscle during incremental cycle ergometry; (2) to examine the influence of accelerometer placements on mean absolute MMG amplitude and MPF values; and (3) to determine the effects of normalization on mean MMG amplitude and MPF values from proximal and distal accelerometer placements. Fifteen adults (10 men and 5 women; mean+/-SD age=23.9+/-3.1 years) performed incremental cycle ergometry tests to exhaustion. Two accelerometers were placed proximal and distal on the VL muscle. Paired t-tests indicated that absolute MMG amplitude values for the proximal accelerometer were greater (p<0.05) than the distal accelerometer at all power outputs. The normalized MMG amplitude also had greater values for the proximal accelerometer at all power outputs, except 50W. There were no differences, however, between proximal and distal accelerometers for absolute MMG MPF, except at 75W, and normalization eliminated this difference. Twenty-seven percent of the subjects exhibited different power output related patterns of responses between accelerometer placements for MMG amplitude and 47% exhibited different patterns for MPF. These findings indicated that normalization did not eliminate the influence of accelerometer placement on MMG amplitude and highlighted the importance of standardizing accelerometer placements to compare MMG values during cycle ergometry.

The effects of electrode orientation on electromyographic amplitude and mean power frequency during cycle ergometry

The purposes of this study were threefold: (1) to compare the power output related patterns of absolute and normalized EMG amplitude and MPF responses for electrode orientations that were approximately parallel and perpendicular to the muscle fibers of the vastus lateralis muscle (VL); (2) to examine the influence of electrode orientation on mean absolute EMG amplitude and MPF values; and (3) to determine the effects of normalization on mean EMG amplitude and MPF values from parallel and perpendicular electrode orientations. Twenty adults (10 men and 10 women mean+/-SD age=23.4+/-3.6 years) performed incremental cycle ergometry tests to exhaustion. Two sets of bipolar surface EMG electrodes were placed approximately parallel and perpendicular to the muscle fibers over the VL. Paired t-tests indicated that absolute EMG amplitude values for the parallel electrode orientation were greater (p<0.05) at 50, 75, and 100W. The normalized EMG amplitude also had greater values for the parallel electrode orientation at 75 and 100W. For absolute EMG MPF, the parallel electrode orientation had greater values for all six power outputs, but after normalization, the perpendicular electrode orientation had a greater value at 75W. Ten percent of the subjects exhibited different power output related patterns of responses between electrode orientations for EMG amplitude and 35% exhibited different patterns for MPF. These findings indicated that normalization reduced, but did not eliminate the influence of electrode orientation and highlighted the importance of standardizing electrode orientation to compare EMG values during cycle ergometry.