Melinda L. Millard-Stafford

Evaluation of the Bod Pod® for assessing body fat in collegiate football players

PURPOSE The purpose of this investigation was to evaluate the accuracy of a new air displacement plethysmograph, BOD POD Body Composition System, for determining %fat in collegiate football players. METHODS Body fatness was estimated from body density (Db), which was measured on the same day using the BOD POD and hydrostatic weighing (HW) in 69 Division IA football players. In addition, 20 subjects were whole body scanned using dual-energy x-ray absorptiometry, DXA (Lunar DPX-L) to assess total body mineral content and %fat. Mineral content and HW determined Db were used to compute %fat from a three-component model (3C; fat, mineral, and residual). RESULTS Test-retest reliability for assessing %fat using the BOD POD (N = 15) was 0.994 with a technical error of measurement of 0.448%. Mean (+/- SEM) Db measured with the BOD POD (1.064 +/- 0.002 g x cc(-1) was significantly greater (P < 0.05) than HW (1.060 +/- 0.002 g x cc(-1)), thus resulting in a lower %fat for the BOD POD (15.1 +/- 0.8%) compared with HW (17.0 +/- 0.8%). Similar results (N = 20) were found for DXA (12.9 +/- 1.2%) and the 3C (12.7 +/- 0.8%) where %fat scores were significantly higher (P < 0.05) than scores determined using the BOD POD (10.9 +/- 1.0%). CONCLUSIONS Db measured with the BOD POD was higher than the criterion HW, thus yielding lower %fat scores for the BOD POD. In addition, BOD POD determined %fat was lower than DXA and 3C determined values in a subgroup of subjects. Assessment of %fat using the BOD POD is reliable and requires minimal technical expertise; however, in this study of collegiate football players, %fat values were underpredicted when compared to HW, DXA, and the 3C model.

Effect of caffeine ingestion on muscular strength and endurance: a meta-analysis.

PURPOSE Our objective was to perform a systematic review and meta-analysis of the research literature assessing the effect of caffeine ingestion on maximal voluntary contraction (MVC) strength and muscular endurance. METHODS Thirty-four relevant studies between 1939 and 2008 were included in the meta-analyses of caffeines effects on MVC strength (n = 27 studies) and muscular endurance (n = 23 studies). Effect sizes (ES) were calculated as the standardized mean difference and meta-analyses were completed using a random-effects model. RESULTS Overall, caffeine ingestion was found to result in a small beneficial effect on MVC strength (overall ES = 0.19, P = 0.0003). However, caffeine appears to improve MVC strength primarily in the knee extensors (i.e., by approximately 7%, ES = 0.37) and not in other muscle groups such as the forearm or the knee flexors. In an attempt to offer a physiological mechanism behind caffeines ability to improve MVC strength, a meta-analysis was run on ES from nine studies that measured percent muscle activation during MVC in trials comparing caffeine versus placebo; the overall ES (0.67) was highly significant (P = 0.00008) and of moderate to large size, thus implicating an effect of caffeine on the CNS. Caffeine ingestion was also found to exert a small beneficial effect on muscular endurance (overall ES = 0.28, P = 0.00005). However, it appears caffeine improves muscular endurance only when it is assessed using open (i.e., by approximately 18%, ES = 0.37) and not fixed end point tests. CONCLUSIONS Overall, caffeine ingestion improves MVC strength and muscular endurance. The effect on strength appears exclusively in the knee extensors, and the effect on muscular endurance appears only detectable with open end point tests.

Use of air displacement plethysmography for estimating body fat in a four-component model.

PURPOSE To compare measurements of body density (D(b)) obtained from air displacement plethysmography (AP) and hydrostatic weighing (HW) and to determine the accuracy of substituting D(b) via AP (D(b)-AP) for D(b) via HW (D(b)-HW) in estimating body fatness (%Fat(4C)) and the composition and density of the fat-free mass (Dffm) from a four-component model (fat, mineral, water, and protein). METHODS D(b) was measured in 50 young adults using AP and HW. Total body water via deuterium dilution, bone mineral content via dual-energy x-ray absorptiometry, and D(b) were used to estimate %Fat(4C). RESULTS D(b)-AP and D(b)-HW were highly correlated (r = 0.89, SEE = 0.008 g x mL(-1)), but D(b)-AP (1.065 +/- 0.003 g x mL(-1)) was significantly higher (P < 0.05) than D(b)-HW (1.058 +/- 0.003 g x mL(-1)), resulting in a mean difference of 2.8%fat. Differences between %Fat(4C-AP) (17.8 +/- 1.2%) and %Fat(4C-HW) (19.3 +/- 1.2%) were significant (P < 0.05), but the SD of the differences (2.3%) was low. When D(b)-AP was used in a four-component model in place of D(b)-HW, the calculated Dffm was significantly higher (1.109 +/- 0.002 vs 1.105 +/- 0.002 g x mL(-1)) based on a higher (P < 0.05) protein fraction (22.0 +/- 0.4% vs 20.6 +/- 0.4%) and lower (P < 0.05) water (71.1 +/- 0.4% vs 72.4 +/- 0.4%) and mineral fractions (7.0 +/- 0.1% vs 7.1 +/- 0.1%). CONCLUSIONS AP yields a higher D(b) than HW and may not be a valid method for measuring D(b) or estimating %fat using densitometry. However, due to relatively small bias and low individual error, D(b)-AP is an acceptable substitute for D(b)-HW when estimating %fat with a four-component model in young adults.

Metabolic and thermoregulatory responses to a simulated American football practice in the heat

Energy cost is a major factor influencing the tolerable thermal load, particularly during exercise in the heat. However, no data exist on the metabolic cost of football practice, although a value of 35% of maximal aerobic capacity (&OV0312;O2max) has been estimated. The energy cost and thermoregulatory response of offensive linemen (OL) was measured wearing different American football ensembles during a simulated half of football practice in the heat. Five collegiate offensive linemen (133 kg, 20% fat, 42 ml·kg-1·min-1 maximal oxygen uptake) completed each of four 60-minute test sessions in an environmental chamber (28° C, 55% relative humidity [RH]) wearing shorts (S), helmet (H), helmet and shoulder pads (HS), and full gear (FUL). Core temperature in the digestive tract (TGI) was obtained using an ingestible sensor. During simulated football drills (e.g., repetitions of drive blocking), exercise intensity ranged from 30 to 81% &OV0312;O2max but averaged 55% &OV0312;O2max (6.7 METS) overall. Blood lactate remained >5 mmol·L-1, and heart rate (HR) averaged 79%HRmax. Equipment had a significant effect on %&OV0312;O2max but only during recovery between drills with HS (61.4 ± 3.7%) compared with H (53.3 ± 6.9%) and S (40.1 ± 8.5%). The TGI was higher (p > 0.05) with HS compared with H at several time-points after 30 minutes. Football practice for OL elicits a significantly higher overall metabolic cost (>6 METS, >50%&OV0312;O2max) than assumed in previous studies. The addition of shoulder pads increases core temperature and energy cost, especially during recovery between active drills in unacclimatized linemen.

Exercise and caffeine improve sustained attention following fatigue independent of fitness status

Background: Exercise improves cognition, but whether fitness status and caffeine modulate this effect remains unclear. Purpose: To determine if sustained attention is improved following exercise with and without caffeine in endurance-trained vs. sedentary adults. Methods: A continuous performance task (CPT), that is, a 20 min measure of sustained attention to assess accuracy and precision, was used to induce mental fatigue. Following the 20 min CPT, trained (n = 12) and sedentary (n = 12) participants completed either 30-min rest or 30-min moderate-intensity cycling below lactate threshold. Exercise trials were completed with placebo and caffeine (3 mg/kg) followed by cycling to volitional fatigue. Results: Exercise, as compared to rest, improved (p < .05) accuracy and precision after a mentally fatiguing task (CPT) and was not different between endurance-trained and sedentary groups. During the CPT, accuracy and precision declined (p < .05) with placebo, but both were maintained with caffeine following both exercise and cycling to volitional fatigue. Mental energy declined (p < .05) after the CPT with placebo but not caffeine. Cycling to volitional fatigue resulted in lower mental energy/greater mental fatigue as compared to baseline and following moderate intensity exercise, for both caffeine and placebo (p < .05). Conclusions: Exercise improved sustained attention following a mentally fatiguing attentional task independent of fitness status; and, when coupled with caffeine, provided greater benefit on the attentional task for accuracy, precision, and mental energy. Although caffeines beneficial effect on sustained attention persisted after cycling to volitional fatigue, it did not prevent a decline in mental energy/increase in mental fatigue.

Carbohydrate ingestion but not mouth rinse maintains sustained attention when fasted

UNLABELLED Carbohydrate (CHO) receptors in the mouth signal brain areas involved in cognitive tasks relying upon motivation and task persistence; however, the minimal CHO dose that improves mental activity is unclear. PURPOSE To determine if CHO (via ingestion or oral rinse) influences sustained attention without eliciting glycemic responses when in a fasted state. METHODS Study A: Six healthy adults completed five treatment trials, ingesting 0-6% CHO solutions to evaluate glycemic response. Peak blood glucose for 6% and 1.5% CHO was greater (p<0.05) than 0% and 0.4% CHO; thus, the low 0.4% CHO was evaluated further. Study B: Following an overnight fast, ten healthy adults completed three trials in a crossover design: 1) 400 ml 0.4% CHO ingested serially via 25 ml boluses, 2) 375 ml 0% CHO control (CON) ingested followed by one 25 ml 6% CHO isocaloric (1.5 g CHO) mouth rinse, and 3) CON ingest followed by CON rinse. Following treatments, a 20 min Continuous Performance Task (CPT) was performed to assess accuracy and precision. RESULTS Accuracy and precision were not different during the first 5 min of CPT. However, accuracy was maintained with CHO ingest (p=1.0) but decreased over 20 min (p<0.05) with both CHO and CON rinse treatments. Precision tended to decline over 20 min CPT with CON (p=0.06) and CHO rinse (p=0.05) but were maintained with CHO ingest (p=1.0). No differences in glycemic responses were observed between treatments. CONCLUSIONS Compared to mouth rinsing CON or CHO (1.5 g in 6% CHO), ingestion of an isocaloric low-CHO drink maintained sustained attention over a mentally fatiguing task and appears effective after fasting without eliciting a glycemic response.

A stethoscope for the knee: Investigating joint acoustical emissions as novel biomarkers for wearable joint health assessment

Each year, millions of Americans endure knee injuries, ranging from simple sprains to ligament tears requiring surgical intervention. Our team is investigating wearable rehabilitation assessment technologies for patients recovering from knee injuries based on the measurement and analysis of the acoustical emissions from the knees. Using miniature electret microphones combined with piezoelectric sensors placed on the surface of the skin at the knee, we measure the sounds from the joint as subjects perform basic flexion/extension exercises and standardized sit-to-stand protocols. We then analyze the consistency of the knee acoustical emissions in the context of the activity, and the angle of the joint, to quantify the health of the joint. We have found, in early pilot studies, promising results differentiating the healthy versus injured knee, and longitudinal changes progressing from acute injury and recovery following rehabilitation. We have also determined that, in healthy subjects, the pattern of acousti...

Fluid Replacement Attenuates Physiological Strain Resulting From Mild Hypohydration Without Impacting Cognitive Performance

PURPOSE The impact of mild hypohydration on physiological responses and cognitive performance following exercise-heat stress (EHS) were examined compared with conditions when fluids were ingested ad libitum (AL) or replaced to match sweat losses (FR). METHODS Twelve unacclimatized, recreationally-active men (22.2 ± 2.4 y) completed 50 min cycling (60%VO2peak) in the heat (32°C; 65% RH) under three conditions: no fluid (NF), AL, and FR. Before and after EHS, a cognitive battery was completed: Trail making, perceptual vigilance, pattern comparison, match-to-sample, and letter-digit recognition tests. RESULTS Hypohydration during NF was greater compared with AL and FR (NF: -1.5 ± 0.6; AL: -0.3 ± 0.8; FR: -0.1 ± 0.3% body mass loss) resulting in higher core temperature (by 0.4, 0.5 °C), heart rate (by 13 and 15 b·min-1), and physiological strain (by 1.3, 1.5) at the end of EHS compared with AL and FR, respectively. Cognitive performance (response time and accuracy) was not altered by fluid condition; however, mean response time improved (p < .05) for letter-digit recognition (by 56.7 ± 85.8 ms or 3.8%; p < .05) and pattern comparison (by 80.6 ± 57.4 ms or 7.1%; p < .001), but mean accuracy decreased in trail making (by 1.2 ± 1.4%; p = .01) after EHS (across all conditions). CONCLUSIONS For recreational athletes, fluid intake effectively mitigated physiological strain induced by mild hypohydration; however, mild hypohydration resulting from EHS elicited no adverse changes in cognitive performance.

Small Beneficial Effect of Caffeinated Energy Drink Ingestion on Strength.

Abstract Collier, NB, Hardy, MA, Millard-Stafford, ML, and Warren, GL. Small beneficial effect of caffeinated energy drink ingestion on strength. J Strength Cond Res 30(7): 1862–1870, 2016—Because caffeine ingestion has been found to increase muscle strength, our aim was to determine whether caffeine when combined with other potential ergogenic ingredients, such as those in commercial energy drinks, would have a similar effect. Fifteen young healthy subjects were used in a double-blind, repeated-measures experimental design. Each subject performed 3 trials, ingesting either a caffeinated energy drink, an uncaffeinated version of the drink, or a placebo drink. The interpolated twitch procedure was used to assess maximum voluntary isometric contraction (MVIC) strength, electrically evoked strength, and percent muscle activation during MVIC of the knee extensors both before and after drink ingestion, and after a fatiguing bout of contractions; electromyographic (EMG) amplitude of the knee extensors during MVIC was also assessed. The mean (±SE) change in MVIC strength from before to after drink ingestion was significantly greater for the caffeinated energy drink compared with placebo [+5.0 (±1.7) vs. −0.5 (±1.5)%] and the difference between the drinks remained after fatigue (p = 0.015); the strength changes for the uncaffeinated energy drink were not significantly different from those of the other 2 drinks at any time. There was no significant effect of drink type on the changes in electrically evoked strength, percent muscle activation, and EMG from before to after drink ingestion. This study indicates that a caffeinated energy drink can increase MVIC strength but the effect is modest and the strength increase cannot be attributed to increased muscle activation. Whether the efficacy of energy drinks can be attributed solely to caffeine remains unclear.

Exercise‐heat stress with and without water replacement alters brain structures and impairs visuomotor performance

Effects of exercise‐heat stress with and without water replacement on brain structure and visuomotor performance were examined. Thirteen healthy adults (23.6 ± 4.2 years) completed counterbalanced 150 min trials of exercise‐heat stress (45°C, 15% RH) with water replacement (EHS) or without (~3% body mass loss; EHS‐DEH) compared to seated rest (CON). Anatomical scans and fMRI Blood‐Oxygen‐Level‐Dependent responses during a visuomotor pacing task were evaluated. Accuracy decreased (P < 0.05) despite water replacement during EHS (−8.2 ± 6.8% vs. CON) but further degraded with EHS‐DEH (−8.3 ± 6.4% vs. EHS and −16.5 ± 10.2% vs. CON). Relative to CON, EHS elicited opposing volumetric changes (P < 0.05) in brain ventricles (−5.3 ± 1.7%) and periventricular structures (cerebellum: 1.5 ± 0.8%) compared to EHS‐DEH (ventricles: 6.8 ± 3.4, cerebellum: −0.7 ± 0.7; thalamus: −2.7 ± 1.3%). Changes in plasma osmolality (EHS: −3.0 ± 2.1; EHS‐DEH: 9.3 ± 2.1 mOsm/kg) were related (P < 0.05) to thalamus (r = −0.45) and cerebellum volume (r = −0.61) which, in turn, were related (P < 0.05) to lateral (r = −0.41) and fourth ventricle volume (r = −0.67) changes, respectively; but, there were no associations (P > 0.50) between structural changes and visuomotor accuracy. EHS‐DEH increased neural activation (P < 0.05) within motor and visual areas versus EHS and CON. Brain structural changes are related to bidirectional plasma osmolality perturbations resulting from exercise‐heat stress (with and without water replacement), but do not explain visuomotor impairments. Negative impacts of exercise‐heat stress on visuomotor tasks are further exacerbated by dehydration.