Raymond W. Thompson

Sources of variance in daily physical activity levels as measured by an accelerometer

PURPOSE To examine sources of variance in objective measures of physical activity in a group of healthy adults (N = 92) participating in a physical activity measurement study. METHODS Physical activity was assessed for up to 21 consecutive days using the Computer Science Applications (CSA) accelerometer. Day-of-the-week effects were evaluated for activity counts (ct.min(-1).d(-1), ct.d(-1)) and time (min.d(-1)) spent in inactivity (0-499 ct), moderate-1 (500-1951 ct), and moderate-2-vigorous activity (> or =1952 ct). Random effects models were employed to estimate variance components for subject, day of the week, and residual error from which the number of days of assessment required to achieve 80% reliability were estimated. RESULTS Physical inactivity was lower on weekend days, and Saturday was the least inactive day of the week for both men and women. Inter-individual variation, or differences between subjects, was proportionally the largest source of variance (55-60% of total) in accelerometer counts and time spent in moderate to vigorous activity. Differences within subjects (intra-individual variation) accounted for 30-45% of the overall variance, and day-of-the-week effects accounted for 1-8%. For activity counts, and time spent in moderate to vigorous activity, at least 3-4 d of monitoring were required to achieve 80% reliability. Reliable measures of physical inactivity required at least 7 d of monitoring. CONCLUSION These findings provide insight for understanding the behavioral variability in the activity patterns of adults and suggest that reliable measures of activity behaviors require at least 7 d of monitoring.

Comparison of three methods for measuring the time spent in physical activity.

PURPOSE Three methods for measuring time spent in daily physical activity (PA) were compared during a 21-d period among 83 adults (38 men and 45 women). METHODS Each day, participants wore a Computer Science and Applications, Inc. (CSA) monitor and completed a 1-page, 48-item PA log that reflected time spent in household, occupational, transportation, sport, conditioning, and leisure activities. Once a week, participants also completed a telephone survey to identify the number of minutes spent each week in nonoccupational walking and in moderate intensity and hard/very hard-intensity PA. Data were analyzed using descriptive statistics and Spearman rank-order correlations. Three equations developed to compute CSA cut points for moderate and hard/very hard PA were also compared with the PA logs and PA survey. RESULTS There was modest to good agreement for the time spent in different PA intensity categories between the three CSA cut point methods (r = 0.43-0.94, P < 0.001). Correlations between the CSA and PA logs ranged from r = 0.22 to r = 0.36, depending on the comparisons. Correlations between the survey items and PA logs were r = 0.26-0.54 (P < 0.01) for moderate and walking activities and r < 0.09 (P > 0.05) for hard/very hard activities. Correlations between the survey items and the CSA min per day varied according to the method used to compute the CSA intensity cut points. CONCLUSIONS The results were consistent with findings from other PA validation studies that show motion sensors, PA logs, and surveys reflect PA; however, these methods do not always provide similar estimates of the time spent in resting/light, moderate, or hard/very hard PA.

The utility of the Digi-walker step counter to assess daily physical activity patterns.

PURPOSE The Digi-Walker step counter is a promising and cost-effective tool to measure physical activity under free-living conditions. Two specific studies were conducted to evaluate the number of steps required to meet current physical activity guidelines. METHODS Thirty-one adults (17 men, 14 women) served as participants. In study 1, we determined the number of steps to complete a mile under two different conditions and three paces. In study 2, we conducted a field trial to examine the relationship between daily step counts and other indices of physical activity. Participants in this study wore a Digi-Walker for 2 consecutive weeks and completed the 7-d physical activity recall (PAR) after each week. RESULTS In study 1, there were no differences in step counts by site, but steps were inversely related to pace, with values ranging from 1330 to 1996. Individual step counts at a specific pace were negatively correlated with height, weight, leg length, and stride length and were positively correlated with body fatness. In study 2, participants had average daily step counts of 11,603 when structured vigorous activity was included and 8265 when only light and moderate activity were measured. Modest correlations were found between step counts and estimated energy expenditure. Similar correlations were observed when step counts were related to minutes of activity per day and minutes of sitting per day. CONCLUSIONS Pedometers provide a useful indicator of daily step counts but variability in activity patterns make it difficult to establish step count guidelines that correspond with other public health guidelines.

The relationship between pedometer-determined ambulatory activity and body composition variables.

OBJECTIVE: To examine the relationship between pedometer-determined ambulatory activity (steps/day) and body composition variables body mass index (BMI) and percentage body fat).DESIGN: Secondary analysis of a cross-sectional objective activity monitoring study for up to 21 consecutive days.SUBJECTS: A total of 109 apparently healthy adults (eight African American males, 23 African-American females, 33 Caucasian males, 45 Caucasian females), age 44.9±15.8 y, BMI=26.9±5.1 kg/m2.MEASUREMENTS: Pedometer-assessed ambulatory activity (steps/day), height and weight, and percentage body fat by bioelectrical impedance.RESULTS: Analyzed as both a continuous and a categorical variable (determined using 25th and 75th percentiles for distribution for steps/day), ambulatory activity was consistently related to body composition variables. Steps/day was inversely correlated with BMI and percentage body fat (r=−0.30, and r=−0.27, respectively, both P<0.01). The consistency of the relationship was also evident when examined using accepted BMI cut-off points for normal-weight, overweight, and obese categories.CONCLUSIONS: Individuals in this small sample with values greater than approximately 9000 steps/day are more frequently classified as normal weight for height. Individuals with values less than approximately 5000 steps/day are more frequently classified as obese. These findings require further corroborative investigation but provide preliminary cutoff points for identifying individuals at risk who may benefit from appropriate physical activity intervention.

Modulation of overload-induced inflammation by aging and anabolic steroid administration

Aging can alter the skeletal muscle growth response induced by overload. The initiation of overload induces muscle extracellular matrix expansion, increased cellularity, and inflammatory gene expression, which are all related to processes important for myofiber growth. These remodeling processes are also biological targets of testosterone. It is not certain how aging affects the inflammatory response to functional overload and whether anabolic steroid administration can alter this response. The effect of anabolic steroid administration on inflammatory processes during functional overload is not known. The purpose of this study was to determine if age altered the skeletal muscle inflammatory response at the onset of functional overload and whether anabolic steroid administration would modulate this response in young or older animals. Five-month and 25 month F344 x BRN rats were given nandrolone decanoate (ND) (6 mg/kg bw/wk) or sham injections for 3 weeks, and then the soleus muscle was overloaded (OV) for 3 days by synergist ablation. ND alone induced a 230% increase in ED1(+) cells in 5 month muscle. Three days of OV had no effect on ED1(+) cell number at either age. OV combined with ND induced a 90% increase in ED2(+) cells in 5 month muscle, while there was no effect of either treatment alone at this age. In 25 month muscle, OV induced a 40% increase in ED2(+) cells. Regardless of age, OV induced muscle TNF-alpha mRNA expression (300%) and IL-6 mRNA expression (900%). ND attenuated OV-induced IL-6 mRNA but not TNF-alpha expression in both age groups. The overload induction of IL-1beta mRNA was 3-fold greater in 25 month muscle (1400%), compared to 5 month muscle (400%). ND administration ablated the overload IL-1beta mRNA induction in 25 month muscle. Anabolic steroid administration can suppress inflammatory cytokine gene expression at the onset of overload and this effect is age dependent.

Musculoskeletal Changes in Mice from 20–50 cGy of Simulated Galactic Cosmic Rays

Abstract Bandstra, E. R., Thompson, R. W., Nelson, G. A., Willey, J. S., Judex, S., Cairns, M. A., Benton, E. R., Vazquez, M. E., Carson, J. A. and Bateman, T. A. Musculoskeletal Changes in Mice from 20–50 cGy of Simulated Galactic Cosmic Rays. Radiat. Res. 172, 21-29 (2009). On a mission to Mars, astronauts will be exposed to a complex mix of radiation from galactic cosmic rays. We have demonstrated a loss of bone mass from exposure to types of radiation relevant to space flight at doses of 1 and 2 Gy. The effects of space radiation on skeletal muscle, however, have not been investigated. To evaluate the effect of simulated galactic cosmic radiation on muscle fiber area and bone volume, we examined mice from a study in which brains were exposed to collimated iron-ion radiation. The collimator transmitted a complex mix of charged secondary particles to bone and muscle tissue that represented a low-fidelity simulation of the space radiation environment. Measured radiation doses of uncollimated secondary particles were 0.47 Gy at the proximal humerus, 0.24–0.31 Gy at the midbelly of the triceps brachii, and 0.18 Gy at the proximal tibia. Compared to nonirradiated controls, the proximal humerus of irradiated mice had a lower trabecular bone volume fraction, lower trabecular thickness, greater cortical porosity, and lower polar moment of inertia. The tibia showed no differences in any bone parameter. The triceps brachii of irradiated mice had fewer small-diameter fibers and more fibers containing central nuclei. These results demonstrate a negative effect on the skeletal muscle and bone systems of simulated galactic cosmic rays at a dose and LET range relevant to a Mars exploration mission. The presence of evidence of muscle remodeling highlights the need for further study.

Effect of the slow-component rise in oxygen uptake on VO2max

During constant-rate high-intensity (CRHI) exercise lasting longer than 3 min, VO2 has been reported to exceed VO2max measured with a traditional graded exercise test (GXT). This could be because VO2max was not achieved on the GXT or because the factors responsible for the slow-component rise in VO2 alter VO2max. The objective of this study was to test the hypothesis that the slow-component rise in VO2 measured during CRHI running leads to a total VO2 that exceeds VO2max measured during a running GXT. VO2max was determined in eight highly trained individuals using data collected from five grade-incremented, treadmill-running GXT. Each subject demonstrated a definitive plateau of VO2 as a function of exercise intensity. Three VO2max values based on different approaches for representing the VO2max plateau were obtained. Subjects also completed two exhaustive CRHI bouts of treadmill running lasting 7-13 min at speeds estimated from the ACSM equation to elicit an average of 99 +/- 5% VO2max. The mean (+/- SD) VO2peak determined during the CRHI runs (4.17 +/- 0.9 l.min-1) was not different form or less than the three VO2max values (4.19-4.32 +/- 0.09 l.min-1). We conclude that in highly trained individuals, the slow-component rise in VO2 during CRHI treadmill running does not lead to a total VO2 that exceeds the VO2max measured during a running graded exercise test.

A Temporal Validation of Scoring Algorithms for the 7-Day Physical Activity Recall

The 7-day physical activity recall (PAR) is one of the most commonly used activity assessments in the exercise science field. The purpose of this study was to evaluate the convergent validity of several PAR-scoring algorithms against a temporally matched measure from an accelerometry-based activity monitor. The participants (n = 24) in the study wore a Tritrac monitor for a period of 8 days and completed a structured PAR interview to recall their activity over the same time frame. The raw energy expenditure (EE) estimate from the Tritrac was found to underpredict the magnitude of the PAR estimate, but the correlation between measures was high (r = .72). The correspondence in EE was better, and the correlation between measures were higher (r = .84 to r = .95) when alternative PAR and Tritrac scoring algorithms were tested. There was no evidence of memory decay, as the correlation remained consistent across all 7 days of recall. The results support the continued use of the PAR for exercise science and epidemiological research and suggest that an alternative PAR scoring system that incorporates sitting time as rest may improve the validity of the assessment.

Smooth muscle γ-actin promoter regulation by RhoA and serum response factor signaling

Abstract Smooth muscle γ-actin (SMGA) is both an early marker of smooth muscle cell differentiation, which demonstrates an expression pattern restricted to smooth muscle and the post meiotic spermatocyte. Serum response factor (SRF) DNA-binding is an important regulator of muscle differentiation, including SMGA expression during smooth muscle cell differentiation. RhoA, a low molecular weight GTPase protein, can regulate cardiac, skeletal, and smooth muscle differentiation through SRF-dependent mechanisms. This studys purpose was to examine RhoA expression during smooth muscle cell development, and determine if the SMGA promoter activity is sensitive to RhoA-mediated signaling through SRF. Additionally, the study identified the promoter regulation modifying SMGA expression by RhoA signaling. Western blot analysis of embryonic chick gizzard whole protein extracts during 5 to 14 days of development demonstrated a large induction of RhoA (10-fold) and β1 integrin expression at day 8, which corresponds to the time SMGA expression and differentiation are occurring. Transient transfections in CV-1 fibroblast cells demonstrated that co-overexpression of SRF and RhoA could induce a 40-fold induction of −176 bp SMGA promoter activity. Mutational analysis demonstrated that serum response element (SRE)-1, but not SRE2, was necessary for RhoA/SRF activation of the SMGA promoter. Deletion analysis revealed that although SRE1 was necessary for SMGA promoter activation by RhoA and SRF, it was not sufficient, implicating a possible obligatory role of additional promoter sequences in the response. Overexpression of a mutated SRF protein that was unable to bind DNA demonstrated that the 40-fold RhoA/SRF activation was largely dependent on SRF binding to the SMGA promoter. Thus, as the SMGA promoter appears to be a target of RhoA-mediated transcriptional regulation, the uncovering of these signaling mechanisms effecting SMGA promoter activity should provide a regulatory paradigm that can then be examined during the regulation of other smooth muscle genes.

REGULATION OF ANDROGEN RECEPTOR EXPRESSION AT THE ONSET OF FUNCTIONAL OVERLOAD IN RAT PLANTARIS MUSCLE

Skeletal muscle androgen receptor (AR) expression at the onset of functional overload (OV) has not been well described. It is also not known if overload and/or anabolic steroid differentially regulate AR expression. The purpose of this study was to examine AR gene expression at the onset of functional OV in rat plantaris muscle with and without nandrolone decanoate (ND) administration. The functional significance of AR protein induction was examined using skeletal alpha-actin promoter activity in transiently transfected CV-1 fibroblast cells. Male Sprague-Dawley rats ( approximately 125 g) were functionally overloaded for 1, 3, 7, or 21 days. A subset of animals was given an ND (6 mg/kg) injection at day 0 and then overloaded for 3 days. Control animals underwent sham surgeries. AR protein concentration increased 106 and 279% after 7 and 21 days of OV, respectively. AR mRNA increased 430% after 7 days of OV. AR protein expression in C2C12 murine myotubes subjected to 1% chronic radial stretch for 18 h was elevated 101% compared with control. ND treatment increased AR protein concentration 1,300% compared with controls, and there was no additional effect when ND and OV were combined. ND with 3 days of OV treatment increased AR mRNA expression 50% compared with control. AR overexpression in transiently transfected CV-1 fibroblast cells increased -424 bp skeletal alpha-actin promoter activity 80 to 1,800% in a dose-dependent fashion. Co-overexpression of either serum response factor (SRF) or active RhoA with AR overexpression induced a synergistic 36- and 28-fold induction of skeletal alpha-actin promoter. Cotransfection of AR, SRF, and active RhoA induced 180-fold increase in skeletal alpha-actin promoter activity. In conclusion, AR protein expression is increased after 7 days of functional OV, and this induction is regulated pretranslationally. AR induction in conjunction with SRF and RhoA signaling may be an important regulator of gene expression during overload-induced muscle growth.