Publications

  • Brian L Tracy, Cady E F Hart
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    ABSTRACT: There has been relatively little longitudinal, controlled investigation of the effects of yoga on general physical fitness, despite the widespread participation in this form of exercise. The purpose of this exploratory study was to examine the effect of short-term Bikram™ yoga training on general physical fitness. Young healthy adults were randomized to yoga training (N=10, 29 ± 6 yrs, 24 sessions in eight weeks) or a control group (N=11, 26 ± 7 yrs). Each yoga training session consisted of 90 min of standardized, supervised postures performed in a heated and humidified studio. Isometric deadlift strength, handgrip strength, lower back/hamstring and shoulder flexibility, resting heart rate and blood pressure, maximal oxygen consumption (treadmill), and lean and fat mass (DEXA) were measured before and after training. Yoga subjects exhibited increased deadlift strength, substantially increased lower back/hamstring flexibility, increased shoulder flexibility, and modestly decreased body fat compared with Control. There were no changes in handgrip strength, cardiovascular measures, or maximal aerobic fitness. In summary, this short-term yoga training protocol produced beneficial changes in musculoskeletal fitness that were specific to the training stimulus.
    The Journal of Strength and Conditioning Research 05/2012; · 1.80 Impact Factor
  • Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE. 01/2009; 41.
  • Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE. 01/2009; 41.
  • Cady E F Hart, Brian L Tracy
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    ABSTRACT: Exercise training programs can increase strength and improve submaximal force control, but the effects of yoga as an alternative form of steadiness training are not well described. The purpose was to explore the effect of a popular type of yoga (Bikram) on strength, steadiness, and balance. Young adults performed yoga training (n = 10, 29 +/- 6 years, 24 yoga sessions in 8 weeks) or served as controls (n = 11, 26 +/- 7 years). Yoga sessions consisted of 1.5 hours of supervised, standardized postures. Measures before and after training included maximum voluntary contraction (MVC) force of the elbow flexors (EF) and knee extensors (KE), steadiness of isometric EF and KE contractions, steadiness of concentric (CON) and eccentric (ECC) KE contractions, and timed balance. The standard deviation (SD) and coefficient of variation (CV, SD/mean force) of isometric force and the SD of acceleration during CON and ECC contractions were measured. After yoga training, MVC force increased 14% for KE (479 +/- 175 to 544 +/- 187 N, p < 0.05) and was unchanged for the EF muscles (219 +/- 85 to 230 +/- 72 N, p > 0.05). The CV of force was unchanged for EF (1.68 to 1.73%, p > 0.05) but was reduced in the KE muscles similarly for yoga and control groups (2.04 to 1.55%, p < 0.05). The variability of CON and ECC contractions was unchanged. For the yoga group, improvement in KE steadiness was correlated with pretraining steadiness (r = -0.62 to -0.84, p < 0.05); subjects with the greatest KE force fluctuations before training experienced the greatest reductions with training. Percent change in balance time for individual yoga subjects averaged +228% (19.5 +/- 14 to 34.3 +/- 18 seconds, p < 0.05), with no change in controls. For young adults, a short-term yoga program of this type can improve balance substantially, produce modest improvements in leg strength, and improve leg muscle control for less-steady subjects.
    The Journal of Strength and Conditioning Research 10/2008; 22(5):1659-69. · 1.80 Impact Factor
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    ABSTRACT: To determine the similarity of motor variability in proximal muscles, young and elderly adults performed steady elbow flexor (EF) and knee extensor (KE) contractions separately (SEP; at 2.5, 30, and 65% of maximum) and simultaneously (SIM; at 2.5 and 30% of maximum), with (VIS) and without (NVIS) visual feedback. Between-muscle correlations of fluctuation amplitude (SD, CV of force), time-based cross-correlations (CC), force power spectra, and frequency-based coherence (COH) values were computed from the concurrent force records. Correlations of fluctuation amplitude ranged from r = 0.34 to 0.86 (P < 0.05) across forces, SEP/SIM, and vision conditions, but were absent for 2.5% NVIS. The relatively low CC values for SIM (r = 0.22-0.33) were stronger for elderly than young adults. The vast majority of the power in the force fluctuations was <4 Hz for all records. Weak COH peaks were only observed <2 Hz for elderly and between 3 and 4 Hz for young, and COH was slightly stronger for elderly below 3 Hz for the 30% MVC target force. The correlations in force fluctuation amplitude suggest that the EF and KE motor neuron pools similarly transform the oscillating synaptic input and may influence each other. The cross-correlations suggest the remote motor neuron pools are influenced similarly in time by a common source of excitation, perhaps more coherently for elderly adults at low frequencies.
    Experimental Brain Research 05/2008; 189(2):159-70. · 2.22 Impact Factor
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    Brian L Tracy
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    ABSTRACT: The visual correction employed during isometric contractions of large proximal muscles contributes variability to the descending command and alters fluctuations in muscle force. This study explored the contribution of visuomotor correction to isometric force fluctuations for the more distal dorsiflexor (DF) and plantarflexor (PF) muscles of the ankle. Twenty-one healthy adults performed steady isometric contractions with the DF and PF muscles both with (VIS) and without (NOVIS) visual feedback of the force. The target forces exerted ranged from 2.5% to 80% MVC. The standard deviation (SD) and coefficient of variation (CV) of force was measured from the detrended (drift removed) VIS and NOVIS steadiness trials. Removal of VIS reduced the CV of force by 19% overall. The reduction in fluctuations without VIS was significant across a large range of target forces and was more consistent for the PF than the DF muscles. Thus, visuomotor correction contributes to the variability of force during isometric contractions of the ankle dorsiflexors and plantarflexors.
    Human Movement Science 01/2008; 26(6):796-807. · 2.06 Impact Factor
  • Brian L. Tracy, Brandon C. Chapman
    Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE. 01/2008; 40.
  • Brian L Tracy
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    ABSTRACT: This study determined the amplitude of force fluctuations for the ankle dorsiflexor (DF) and plantarflexor (PF) muscles of young and elderly adults. Maximal voluntary contraction (MVC) force and isometric DF and PF steadiness (2.5-80% MVC) was assessed in 11 young (23+/-3 years, 5 women, 6 men) and 10 elderly (73+/-6 years, 5 women, 5 men) adults. The coefficient of variation (CV) and power spectrum of the force was measured from the steadiness trials. MVC force was lower for elderly adults for PF (38% lower, P=0.002) but not DF (20% lower, P=0.14). For PF, the CV of force was greater for elderly than young adults at 2.5% (2.64 vs. 1.71%) and 5% MVC (1.78 vs. 1.24%), similar at 10, 50, and 80% MVC, and greater for young than elderly at the 30% MVC target force. For DF, the CV of force was similar for young and elderly at all target forces (P>0.05). The CV of force was 49% lower for the PF compared with DF muscles across all target forces (P<0.0001). This difference was significantly greater at the 2.5 (58%), 5 (58%), and 10% MVC (44%) target forces compared with higher target forces. The power spectra of the force fluctuations for both muscles were consistently dominated by frequencies below 2 Hz. For elderly adults, the neuromuscular factors that underlie both muscle strength and force fluctuations during low-force contractions are impaired in the ankle plantarflexors but not the dorsiflexors.
    Arbeitsphysiologie 11/2007; 101(5):629-36. · 2.66 Impact Factor
  • Seth J Welsh, Devin V Dinenno, Brian L Tracy
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    ABSTRACT: The purpose was to determine the contribution of visual feedback and the effect of aging on the variability of knee extensor (KE) muscle force and motor unit (MU) discharge. Single MUs were recorded during two types of isometric trials, (1) visual feedback provided (VIS) and then removed (NOVIS) during the trial (34 MUs from young, 32 from elderly), and (2) only NOVIS (66 MUs from young, 77 from elderly) during the trial. Recruitment threshold (RT) ranged from 0-37% MVC. Standard deviation (SD) and coefficient of variation (CV) of muscle force and MU interspike interval (ISI) was measured during steady contractions at target forces ranging from 0.3 to 54% MVC. Force drift (<0.5 Hz) was removed before analysis. VIS/NOVIS trials: the decrease in the CV of ISI from VIS to NOVIS was greater for MUs from elderly (12.5 +/- 4.1 to 9.94 +/- 2.6%) than young (10.6 +/- 3.3 to 10.3 +/- 2.8%, age group x vision interaction, P = 0.006). The change in CV of force from VIS to NOVIS was significantly greater for elderly (1.45 to 1.05%) than young (1.42 to 1.41%). NOVIS only trials: for all MUs, the average RT (6.6 +/- 7.7 % MVC), target force above RT (1.20 +/- 2.7% MVC), SD of ISI (0.012 +/- 0.005 s), and CV of ISI (11.1 +/- 3.3%) were similar for young and elderly MUs. The CV of force was similar between age groups for trials between 0 and 3% MVC (1.74 +/- 0.74%) and was greater for young subjects from 3 to 10% MVC (1.47 +/- 0.5 vs. 1.21 +/- 0.4%) and >10% MVC (1.44 +/- 0.6 vs. 1.01 +/- 0.3%). The CV of ISI was similar between age groups for MUs in 0-3, 3-10, and >10% bins of RT. Thus, the contribution of visuomotor correction to the variability of motor unit discharge and force is greater for elderly adults. The presence of visual feedback appears to be necessary to find greater discharge variability in motor units from the knee extensors of elderly adults.
    Experimental Brain Research 05/2007; 179(2):219-33. · 2.22 Impact Factor
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    ABSTRACT: To determine the contribution of visuomotor correction to increased force fluctuations in the elbow flexor and knee extensor muscles of elderly adults. Young (N = 22, 23 +/- 3 yr) and elderly (N = 23, 74 +/- 7 yr) adults performed constant-force contractions at target forces of 2.5, 30, and 65% MVC. Visual feedback was provided (6-8 s) and then removed (6-8 s). After removal of drift (< 0.5 Hz) from the force, the standard deviation (SD) and coefficient of variation (CV) of force were calculated from vision and no-vision data. Maximal voluntary contraction (MVC) force was 19% lower for elbow flexors and 37% lower for knee extensors in elderly adults than in young adults. Overall, the CV of force was 27% greater in the vision condition compared with the no-vision condition. The CV of force for vision was greater for elderly adults than for young adults at the 2.5% MVC target force and lower at 30 and 65% MVC. For the 2.5% MVC target force, the decline in CV of force from vision to no vision was greater for elderly adults than for young adults. At 30 and 65% MVC, the decline was significant but similar for young and elderly adults. For elbow flexors, the change in power from vision to no vision was greater for 0- to 4-Hz (reduced power) and 8- to 12-Hz (increased power) frequencies for elderly adults compared with young adults. Visuomotor correction contributed to force fluctuations in large proximal muscles. The contribution was greater for healthy elderly adults at low forces. Visuomotor processes thus contributed to the age-related increase in force fluctuations.
    Medicine &amp Science in Sports &amp Exercise 03/2007; 39(3):469-79. · 4.48 Impact Factor
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    ABSTRACT: The purpose of this study was to determine motor output variability for different muscles in the same individuals. Ten young (21.7 +/- 3.4 years) and ten elderly (72.1 +/- 3.9 years) men underwent assessment of maximal isometric (MVC) and dynamic (1-RM) strength, and performed constant-force (2-50% MVC), constant-load (5-50% 1-RM load), and unloaded postural contractions as steadily as possible with the first dorsal interosseus (FDI), elbow flexors (EF), and knee extensors (KE). The coefficient of variation (CV) of force for isometric contractions and the standard deviation (SD) of acceleration for concentric, eccentric, and postural contractions were calculated. The 1-RM load, the CV of force for four of five isometric target forces, and the SD of acceleration during postural contractions were correlated between the EF and KE muscles. MVC force, 1-RM load, and SD of acceleration during postural contractions were not correlated between the FDI/EF or FDI/KE. The CV of force was correlated between the FDI/EF and FDI/KE for two of five isometric target forces. The SD of acceleration during concentric and eccentric contractions was not correlated between muscles. The normalized fluctuations during isometric contractions were greater for the FDI compared with the EF and KE. Elderly adults displayed greater fluctuations only for the FDI during low-force isometric and postural contractions. The dominant frequency of fluctuations was similar for the EF and KE muscles. The correlated fluctuations for the EF and KE muscles, within subjects, suggests that the two motor neuron pools transform the various neural inputs similarly.
    Experimental Brain Research 02/2007; 176(3):448-64. · 2.22 Impact Factor
  • Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE. 01/2007; 39.
  • Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE. 01/2007; 39.
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    Brian L Tracy, Roger M Enoka
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    ABSTRACT: This study was conducted to determine the effect of steadiness training with light loads in the knee extensors of elderly adults. Twenty-one elderly adults (72 +/- 4.6 yr) performed 16 wk of closely supervised knee extensor training that consisted of lifting and lowering 30% of the one-repetition maximum (1-RM) load as steadily as possible (10 reps per set, three sets per session, three sessions per week). Nine subjects served in a control group. Unilateral and bilateral maximal voluntary contraction (MVC) force; 1-RM load; force fluctuations during submaximal isometric, concentric, and eccentric contractions; timed functional performance (gait, chair rise, stair ascent and descent); muscle volume via magnetic resonance imaging (MRI); and the electromyogram (EMG) were measured. The training group exhibited modest average gains in MVC force and 1-RM load; muscle volume and EMG were unaltered. Although isometric steadiness was unchanged on average, training elicited the greatest improvements in the least steady subjects. Force fluctuations during concentric and eccentric contractions were significantly reduced. Of 21 subjects, 14 responded to training with gains in 1-RM load greater than the typical change (6%) in the control group. Before training, these responders exhibited greater force during bilateral compared with unilateral contractions. The small changes in physical functional performance were similar for the training and control groups. The training group could lift the pretraining 1-RM load 4.6 times after training (5.6 times for responders). Steadiness training with the knee extensors thus produced neural adaptations that increased strength in elderly adults who exhibited bilateral facilitation, improved isometric steadiness in unsteady subjects, improved steadiness during concentric and eccentric contractions, and enhanced the ability to lift heavy loads repeatedly.
    Medicine &amp Science in Sports &amp Exercise 05/2006; 38(4):735-45. · 4.48 Impact Factor
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    ABSTRACT: This study assessed age and sex effects on muscle fibre adaptations to heavy-resistance strength training (ST). Twenty-two young men and women (20-30 years old) and 18 older men and women (65-75 years old) completed 9 weeks of heavy-resistance knee extension exercises with the dominant leg 3 days week(-1); the non-dominant leg served as a within-subject, untrained control. Bilateral vastus lateralis muscle biopsies were obtained before and after ST for analysis of type I, IIa and IIx muscle fibre cross-sectional area (CSA) and fibre type distribution. One-repetition maximum (1-RM) strength was also assessed before and after ST. ST resulted in increased CSA of type I, IIa and IIx muscle fibres in the trained leg of young men, type I and IIa fibres in young women, type IIa fibres in older men, and type IIx fibres in older women (all P<0.05). Analysis of fibre type distribution revealed a significant increase in the percentage of type I fibres (P<0.05) along with a decrease in type IIx fibres (P=0.054) after ST only in young women. There were no significant changes in muscle fibre CSA or fibre type distribution in the untrained leg for any group. All groups displayed significant increases in 1-RM (27-39%; all P<0.01). In summary, ST led to significant increases in 1-RM and type II fibre CSA in all groups; however, age and sex influence specific muscle fibre subtype responses to ST.
    Experimental Physiology 03/2006; 91(2):457-64. · 2.79 Impact Factor
  • Brian L. Tracy, Halden J. Clark, Ryan L. Smith
    Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE. 01/2006; 38.
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    ABSTRACT: The purpose of this study was to determine the effect of task-specificity on knee extensor steadiness adaptations in functionally limited older adults. Twenty-four functionally limited older adults (74.6+/-7.6 years: 22 women, 2 men) completed a 10-week control period followed by 10 weeks (2 days/week) of resistance (RT), functional (FT) (practicing everyday tasks, i.e., chair rises) or functional + resistance (FRT) training, which featured both shortening and lengthening movements. During testing, subjects performed a steady isometric [10, 25, 50% of maximal voluntary contraction (MVC)] and shortening/lengthening (5, 30, 65% of MVC) knee extensor contractions. There were no steadiness (isometric, shortening or lengthening contractions) changes in the control period and no adaptations in isometric steadiness due to training. RT induced a 37% reduction in shortening fluctuations at 5% of MVC and 35% reduction in lengthening fluctuations at both 30% and 65% of MVC. FRT induced a 60% reduction in shortening fluctuations at 30% of MVC. No adaptations in dynamic steadiness were observed in the FT group. Further analysis indicated that those who were the least steady at baseline showed the greatest training effects during isometric (RT: R (2)=0.25, FRT: R (2)=0.49, FT: R (2)=0.38), shortening (RT: R (2)=0.36, FRT: R (2)=0.36, FT: R (2)=0.35) and lengthening (RT: r (2)=0.29, FRT: r (2)=0.44) contractions. In conclusion, steadiness improvements in groups performing resistance exercise, without a concomitant improvement in the FT group, supports a role for task-specificity in explaining steadiness adaptations, particularly for unsteady older adults.
    Arbeitsphysiologie 01/2006; 95(5-6):436-46. · 2.66 Impact Factor
  • Seth J. Welsh, Devin V. Dinenno, Brian L. Tracy
    Medicine and Science in Sports and Exercise - MED SCI SPORT EXERCISE. 01/2006; 38.
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    ABSTRACT: Variability of motor unit discharge is a likely contributor to the greater force fluctuations observed in old adults at low muscle forces. We sought to determine whether the variability of motor unit discharge rate underlies the fluctuations in force during steady contractions across a range of forces in young (n = 11) and old (n = 14) adults. The coefficient of variation (CV) for discharge rate and force were measured during a force-matching task as the first dorsal interosseous muscle performed isometric contractions. The recruitment thresholds of the 78 motor units ranged from 0.04% to 34% of maximal voluntary contraction (MVC) force. The CV for discharge rate ranged from 7.6% to 46.2% and was greater (P < 0.05) for old adults (21.5% +/- 7.7%) than young adults (17.3% +/- 8.1%). Although the CV for force was similar for young and old subjects (2.53% +/- 1.6%) across all target forces, it was greater for old adults at the lowest forces. Furthermore, there was a positive relation (r2 = 0.20, P < 0.001) between the CV for force and the CV for discharge rate across the range of recruitment thresholds. This relation was significant for old adults (r2 = 0.30, P < 0.001), but not for young adults (r2 = 0.06, P > 0.05). Thus, the normalized variability (CV) of motor unit discharge was greater in old adults and was related to the amplitude of force fluctuations across a broader range of forces than previously examined. These findings underscore the contribution of variability of motor unit activity to motor output in normal human aging.
    Muscle & Nerve 11/2005; 32(4):533-40. · 2.31 Impact Factor
  • Medicine &amp Science in Sports &amp Exercise 04/2005; 37(5):S162. · 4.48 Impact Factor

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