John S. Fitzgerald

Association Between Vitamin D Status and Maximal-Intensity Exercise Performance in Junior and Collegiate Hockey Players.

Abstract Fitzgerald, JS, Peterson, BJ, Warpeha, JM, Johnson, SC, and Ingraham, SJ. Association between vitamin D status and maximal-intensity exercise performance in junior and collegiate hockey players. J Strength Cond Res 29(9): 2513–2521, 2015—Recent evidence suggests that athletes are at risk for poor vitamin D status. This study used a cross-sectional design to investigate the strength of association between 25-hydroxyvitamin D (25(OH)D) concentration and measures of maximal-intensity exercise performance in competitive hockey players. Fifty-three collegiate and junior male ice hockey players training near Minneapolis, MN (44.9° N latitude) participated in the study during the off-season (May 16–June 28). Circulating 25(OH)D concentration, grip strength, vertical jump performance, and power production during the Wingate Anaerobic Test (WAnT) were evaluated. Despite no athletes with 25(OH)D concentration indicative of deficiency (<20 ng·mL−1), positive bivariate correlations were detected between vitamin D status, relative grip strength (p = 0.024), and peak power during the WAnT (p = 0.035). Only for relative grip strength (p = 0.043), did 25(OH)D concentration predict performance after adjusting for level of play, fat-free mass, fat mass, and self-reported total physical activity in sequential linear regression. Vitamin D status was positively associated with starting gradient (p = 0.020) during the squat jump, with higher concentrations associated with increased rate of force development in the initial portion of the jump. Interventional trials should investigate the impact of vitamin D supplementation on maximal-intensity exercise performance outcomes and rate of force development in large samples of vitamin D–deficient athletes while controlling for training exposure. Our data indicate that if vitamin D status is causally related to maximal-intensity exercise performance in athletes, the effect size is likely small.

The Effects of Caffeine on Vertical Jump Height and Execution in Collegiate Athletes.

Abstract Bloms, LP, Fitzgerald, JS, Short, MW, and Whitehead, JR. The effects of caffeine on vertical jump height and execution in collegiate athletes. J Strength Cond Res 30(7): 1855–1861, 2016—Caffeine ingestion elicits a variety of physiological effects that may be beneficial to maximal-intensity exercise performance, although its effectiveness and physical mechanism of action enhancing ballistic task performance are unclear. The purpose of this study was to examine the effects of caffeine ingestion on vertical jump height and jump execution in Division I collegiate athletes. The study used a single-blind, randomized, crossover design. Athletes (n = 25) consumed either caffeine (5 mg·kg−1) or placebo. After a 60-minute waiting period, athletes performed 3 squat jumps (SJ) and 3 countermovement jumps (CMJ) while standing on a force platform. Jump height and execution variables were calculated from mechanography data. In comparison with placebo, caffeine increased SJ height (32.8 ± 6.2 vs. 34.5 ± 6.7 cm; p = 0.001) and CMJ height (36.4 ± 6.9 vs. 37.9 ± 7.4 cm; p = 0.001). Peak force (p = 0.032) and average rate of force development (p = 0.037) were increased during the CMJ in the caffeine trail compared with the control. Time to half peak force was the only execution variable improved with caffeine (p = 0.019) during the SJ. It seems that caffeine affects both height and execution of jumping. Our data indicate that the physical mechanism of jump enhancement is increased peak force production or rate of force development during jumping depending on technique. The physical mechanism of jump enhancement suggests that the ergogenic effects of caffeine may transfer to other ballistic tasks involving the lower-body musculature in collegiate athletes.

Division I Hockey Players Generate More Power Than Division III Players During on- and Off-Ice Performance Tests.

Abstract Peterson, BJ, Fitzgerald, JS, Dietz, CC, Ziegler, KS, Ingraham, SJ, Baker, SE, and Snyder, EM. Division I hockey players generate more power than Division III players during on- and off-ice performance tests. J Strength Cond Res 29(5): 1191–1196, 2015—Current research has found anthropometric and physiological characteristics of hockey players that are correlated to performance. These characteristics, however, have never been examined to see whether significant differences exist between on- and off-ice performance markers at different levels of play; Division I, Elite Junior, and Division III. The purpose of this study was to examine the differences that may exist between these characteristics in Division I (24), Elite Junior (10), and Division III hockey (11) players. Forty-five (age: 18–24 years) hockey players completed anthropometric, on-ice, and off-ice tests to ascertain average measures for each division of play. On-ice testing was conducted in full hockey gear and consisted of acceleration, top-speed, and on-ice repeated shift test (RST). Off-ice tests included vertical jump, Wingate, grip strength, and a graded exercise test performed on a skating treadmill to ascertain their . Division I players had significantly lower body fat than their Division III peers (p = 0.004). Division I players also scored significantly better on measures of anaerobic power; vertical jump (p = 0.001), Wingate peak power (p = 0.05), grip strength (p = 0.008), top speed (p = 0.001), and fastest RST course time (p = 0.001) than their Division III counterparts. There was no significant difference between Division I and Elite Junior players for any on- or off-ice performance variable. The results of this study indicate that performance differences between Division I and Division III hockey players seem to be primarily because of the rate of force production.

Aerobic capacity is associated with improved repeated shift performance in hockey.

Abstract Peterson, BJ, Fitzgerald, JS, Dietz, CC, Ziegler, KS, Ingraham, SJ, Baker, SE, and Snyder, EM. Aerobic capacity is associated with improved repeated shift performance in hockey. J Strength Cond Res 29(6): 1465–1472, 2015—Current research has found conflicting results regarding the relationship between maximal oxygen uptake (V[Combining Dot Above]O2peak) and the repeated sprint ability (RSA) of hockey players. The purpose of this study was to use sport-specific testing methods to investigate this relationship. Forty-five (range, 18–24) college hockey players completed a graded exercise test on a skating treadmill to ascertain their V[Combining Dot Above]O2peak. An on-ice repeated shift test was then conducted to evaluate each players susceptibility to fatigue. First gate, second gate, and total test times were collected on the course and then used to calculate associated decrement scores. Second gate decrement was significantly correlated to V[Combining Dot Above]O2peak (r = −0.31, p = 0.04). Final stage completed during the graded exercise test was also significantly correlated to second gate and total decrement (r = −0.46, p = 0.001; r = −0.32, p = 0.03). No significant correlation was found between either first gate or total decrement score and V[Combining Dot Above]O2peak (r = −0.11, p = 0.46; r = −0.17, p = 0.26). The results of this study indicate that RSA is associated with V[Combining Dot Above]O2peak and final stage completed when using sport-specific testing methods.

Vitamin D status is associated with adiposity in male ice hockey players.

UNLABELLED The prevalence of insufficient vitamin D status is of concern and may negatively affect health and physical performance. PURPOSE The purpose of this study was twofold, as follows: to assess the prevalence of 25-hydroxyvitamin D (25(OH)D) insufficiency among young hockey players and evaluate the association between 25(OH)D concentration and fat mass (FM) after adjusting for covariates. METHODS Data were collected for 53 junior and collegiate ice hockey players residing near Minneapolis, MN (44.9° N) during the off-season (May 16 to June 28). Liquid chromatography-tandem mass spectrometry was used to assess 25(OH)D concentration, and hydrostatic weighing was used to determine FM. Dietary intake and endogenous synthesis of vitamin D were evaluated via a questionnaire. RESULTS Twenty (37.7%) athletes possessed insufficient 25(OH)D concentrations (<32 ng·mL(-1)). Log-transformed 25(OH)D concentration was inversely associated with FM in the athletes (r = -0.52, n = 51, P = 0.001). After controlling for measured covariates using sequential linear regression, the adjusted R2 change value indicated that 8.1% of the variability in (log of) 25(OH)D concentration was predicted by FM (P = 0.005). CONCLUSIONS The findings of this study demonstrate an inverse association between FM and vitamin D status after adjusting for environmental, dietary, and anthropometric predictors in a sample population of athletes. Athletes with higher levels of adiposity may be at increased risk of poor vitamin D status.

Vitamin D status and V[combining dot above]O2peak during a skate treadmill graded exercise test in competitive ice hockey players.

Abstract Fitzgerald, JS, Peterson, BJ, Warpeha, JM, Wilson, PB, Rhodes, GS, and Ingraham, SJ. Vitamin D status and V[Combining Dot Above]O2peak during a skate treadmill graded exercise test in competitive ice hockey players. J Strength Cond Res 28(11): 3205–3210, 2014—Vitamin D status has been associated with cardiorespiratory fitness (CRF) in cross-sectional investigations in the general population. Data characterizing the association between 25-hydroxyvitamin D (25(OH)D) concentration and CRF in athletes are lacking. Junior and collegiate ice hockey players were recruited from the Minneapolis, MN (44.9° N), area during the off-season period (May 16–June 28). The purpose of this study was to examine the cross-sectional association between 25(OH)D concentration and CRF in a sample population of competitive ice hockey players. Circulating 25(OH)D level was assessed from a capillary blood sample analyzed using liquid chromatography-tandem mass spectrometry. V[Combining Dot Above]O2peak during a skate treadmill graded exercise test (GXT) was used to assess CRF. Data on both 25(OH)D concentration and V[Combining Dot Above]O2peak were available for 52 athletes. Insufficient 25(OH)D concentrations were found in 37.7% of the athletes (<32 ng·ml−1). Vitamin D status was not significantly associated with any physiological or physical parameter during the skate treadmill GXT.

Reliability of Triaxial Accelerometry for Measuring Load in Men's Collegiate Ice-Hockey.

Abstract Van Iterson, EH, Fitzgerald, JS, Dietz, CC, Snyder, EM, and Peterson, BJ. Reliability of triaxial accelerometry for measuring load in mens collegiate ice hockey. J Strength Cond Res 31(5): 1305–1312, 2017—Wearable microsensor technology incorporating triaxial accelerometry is used to quantify an index of mechanical stress associated with sport-specific movements termed PlayerLoad. The test-retest reliability of PlayerLoad in the environmental setting of ice hockey is unknown. The primary aim of this study was to quantify the test-retest reliability of PlayerLoad in ice hockey players during performance of tasks simulating game conditions. Division I collegiate male ice hockey players (N = 8) wore Catapult Optimeye S5 monitors during repeat performance of 9 ice hockey tasks simulating game conditions. Ordered ice hockey tasks during repeated bouts included acceleration (forward or backward), 60% top-speed, top-speed (forward or backward), repeated shift circuit, ice coasting, slap shot, and bench sitting. Coefficient of variation (CV), intraclass correlation coefficient (ICC), and minimum difference (MD) were used to assess PlayerLoad reliability. Test-retest CVs and ICCs of PlayerLoad were as follows: 8.6% and 0.54 for forward acceleration, 13.8% and 0.78 for backward acceleration, 2.2% and 0.96 for 60% top-speed, 7.5% and 0.79 for forward top-speed, 2.8% and 0.96 for backward top-speed, 26.6% and 0.95 for repeated shift test, 3.9% and 0.68 for slap shot, 3.7% and 0.98 for coasting, and 4.1% and 0.98 for bench sitting, respectively. Raw differences between bouts were not significant for ice hockey tasks (p > 0.05). For each task, between-bout raw differences were lower vs. MD: 0.06 vs. 0.35 (forward acceleration), 0.07 vs. 0.36 (backward acceleration), 0.00 vs. 0.06 (60% top-speed), 0.03 vs. 0.20 (forward top-speed), 0.02 vs. 0.09 (backward top-speed), 0.18 vs. 0.64 (repeated shift test), 0.02 vs. 0.10 (slap shot), 0.00 vs. 0.10 (coasting), and 0.01 vs. 0.11 (bench sitting), respectively. These data suggest that PlayerLoad demonstrates moderate-to-large test-retest reliability in the environmental setting of male Division I collegiate ice hockey. Without previously testing reliability, these data are important as PlayerLoad is routinely quantified in male collegiate ice hockey to assess on ice physical activity.

Off-Ice Anaerobic Power Does Not Predict On-Ice Repeated Shift Performance in Hockey.

Abstract Peterson, BJ, Fitzgerald, JS, Dietz, CC, Ziegler, KS, Baker, SE, and Snyder, EM. Off-ice anaerobic power does not predict on-ice repeated shift performance in hockey. J Strength Cond Res 30(9): 2375–2381, 2016—Anaerobic power is a significant predictor of acceleration and top speed in team sport athletes. Historically, these findings have been applied to ice hockey although recent research has brought their validity for this sport into question. As ice hockey emphasizes the ability to repeatedly produce power, single bout anaerobic power tests should be examined to determine their ability to predict on-ice performance. We tested whether conventional off-ice anaerobic power tests could predict on-ice acceleration, top speed, and repeated shift performance. Forty-five hockey players, aged 18–24 years, completed anthropometric, off-ice, and on-ice tests. Anthropometric and off-ice testing included height, weight, body composition, vertical jump, and Wingate tests. On-ice testing consisted of acceleration, top speed, and repeated shift fatigue tests. Vertical jump (VJ) (r = −0.42; r = −0.58), Wingate relative peak power (WRPP) (r = −0.32; r = −0.43), and relative mean power (WRMP) (r = −0.34; r = −0.48) were significantly correlated (p ⩽ 0.05) to on-ice acceleration and top speed, respectively. Conversely, none of the off-ice tests correlated with on-ice repeated shift performance, as measured by first gate, second gate, or total course fatigue; VJ (r = 0.06; r = 0.13; r = 0.09), WRPP (r = 0.06; r = 0.14; r = 0.10), or WRMP (r = −0.10; r = −0.01; r = −0.01). Although conventional off-ice anaerobic power tests predict single bout on-ice acceleration and top speed, they neither predict the repeated shift ability of the player, nor are good markers for performance in ice hockey.

Relationship between serum 25-hydroxyvitamin D status and cardiorespiratory fitness: Findings from the National Health and Nutrition Examination Survey

Lowcardiorespiratoryfitness (CRF) and serum25-hydroxyvitaminD (25[OH]D) are associated with increased cardiovascular morbidity and mortality [1–4]. Several studies have suggested that lower serum 25(OH)D is associated with reduced CRF, but these reports were based on selective samples [5–7]. It is important to assess whether these associations are present among individuals in the general population or whether these associations are present only among specific subsets of thepopulation suchas the elderly or thosewith serious chronic diseases. The purpose of this investigation was to examine the association between CRF and serum 25(OH)D utilizing a nationally representative sample of the United States, the National Health and Nutrition Examination Survey (NHANES). NHANES uses home interviews to ascertain demographics, and a subset of participants receive a health examination — including CRF assessment — at mobile examination centers. Participants aged 12–49 were eligible for the CRF assessment, and data from the 2001–2004 NHANES were used for this analysis. CRF was assessed with a submaximal walking protocol conducted on a motorized treadmill (Quinton MedTrack ST65, Cardiac Science, Waukesha, WI). Participants were assigned to one of eight protocols based on a pre-test predicted CRF, which was calculated using sex, age, body mass index (BMI), and self-reported physical activity [8]. The grade and speed of the protocols were chosen so that participants would achieve a heart rate (HR) equal to 75% of an age-predicted maximum. All protocols consisted of two 3min stages, and maximal oxygen uptake (VO2max; ml/kg/min) was estimated by extrapolating HR measured during the submaximal exercise. A linear relationship between oxygen consumption and HR was assumed for the purposes of estimating CRF. Individuals were excluded from the CRF test for a number of reasons, including functional limitations, cardiovascular disease history, respiratory limitations, and heart rate/blood pressure irregularities. CRF values N 75 ml/kg/min were recoded as 75 ml/kg/min because higher values are particularly rare. Serum 25(OH)D was assessed with the DiaSorin radioimmunoassay (DiaSorin Corporation, Stillwater, MN). Pearson correlations were used to examine the bivariate association between CRF and serum 25(OH)D. SPSS Complex Samples general linear model was used to assess serum 25(OH)D as a predictor of CRF while adjusting for covariates and accounting for the complex sampling design of NHANES. Means (standard errors) and proportions were weighted to the United States population using the NHANES supplied population weights. CRF, serum 25(OH)D, and covariate data were available from 5392 participants (out of 21,161). The mean age was 28.9 ± 0.2 years, 48% were females, and 69% were Caucasian. Mean serum 25(OH)D was 24.8 ± 0.3 ng/ml, with 33.4% of participants classified as deficient (b20 ng/ml). Mean VO2max was 40.4 ± 0.3 ml/kg/min, and mean VO2max by 25(OH)D deficiency status is shown in Table 1. Table 2 presents the prevalence of serum 25(OH)D deficiency by quartiles of CRF for men and women. Overall, serum 25(OH)Dwas weakly correlated with CRF in bothmen (r= .11, p b .001) and women (r= .07, p= .001). In sex-specific general linear models including age, race/ethnicity, season (November–April vs. May–October), self-reportedphysical activity, andBMI, serum25(OH)Das a continuous measure was not significantly associated with CRF in men (Beta = .06, p= .095) or women (Beta = .01, p= .669). When analyzed in terms of deficiency, serum 25(OH)D was associated with CRF in men, butnotwomen.Menwith serum25(OH)Ddeficiencyhada1.7 ml/kg/min lower VO2max (p= .001) after controlling for covariates. Exclusion of participants aged b18 years did not significantly influence the results of the multivariate models (data not shown). This is the first study to examine the association between CRF and serum 25(OH)D among individuals in the general population, as previous studies have relied on selective samples. An analysis of a randomized trial investigating statins and muscle performance found an association of r= .29 between serum 25(OH)D and CRF among 200 participants, which is stronger thanwhatwas observed in this study [5]. Two investigations from the Cooper Center Longitudinal Study (CCLS) did not report correlations but did find that serum 25(OH)D was significantly lower in unfit women and men across levels of adiposity [6,7]. Differences in the samples utilized may explain the variation in results between the previous research and the current study. The mean ages were 46 and 50 years for the two CCLS studies [6,7] and 40 years for the statin trial [5], compared to 29 years for the current study. Given that vitamin D synthesis and metabolism is altered with aging [9,10], it is possible that the association between serum 25(OH)D and CRF becomes stronger with advancing age. Additionally, the participants from the two CCLS studies were mostly Caucasian (N90%), of high economic status (70% college graduates), and from the southern United States. The racial/ethnic distribution, economic status, and geographic origin of the participants from the statin trial were not detailed [5], making comparisons to this sample difficult. Strengths of the study include the use of a representative sample of United States population with oversampling of minority groups. Additionally, the adjustment for important covariates allowed for a more accurate estimation of the associations between serum 25(OH)D and CRF. Limitations include the use of a submaximal test to estimate CRF and the younger age range of the participants.

Energy compensation in response to aerobic exercise training in overweight adults

Weight loss from exercise is often less than expected. Putative compensatory mechanisms may limit exercise-induced reductions in body fat and might be proportional to exercise energy expenditure (ExEE). This study was conducted to determine compensation for (the difference between accumulated exercise energy expenditure and changes in body tissue energy stores) and compensatory responses to 1,500 or 3,000 kcal/wk of ExEE. Overweight-to-obese ( n = 36) sedentary men and women were randomized to groups expending 300 or 600 kcal/exercise session, 5 days/wk, for 12 wk. Fourteen participants in the 300-kcal group and 15 in the 600-kcal group completed the study. The primary outcome was energy compensation assessed through changes in body tissue energy stores. Secondary outcomes were putative compensatory responses of resting metabolic rate, food reinforcement, dietary intake, and serum acylated ghrelin and glucagon-like peptide-1. All measures were determined pre- and posttraining. The 3,000 kcal/wk group decreased ( P < 0.01) percentage and kilograms of body fat, while the 1,500 kcal/wk group did not. The 1,500 and 3,000 kcal/wk groups compensated for 943 (-164 to 2,050) and 1,007 (32 to 1,982) kcal/wk (mean, 95% CI, P ≥ 0.93), or 62.9% and 33.6% of ExEE, respectively. Resting metabolic rate and energy intake did not change. Food reinforcement and glucagon-like peptide-1 decreased ( P < 0.02), whereas acylated ghrelin increased ( P ≤ 0.02). Compensation is not proportional to ExEE. Similar energy compensation occurred in response to1,500 and 3,000 kcal/wk of ExEE. ExEE of 3,000 kcal/wk is sufficient to exceed compensatory responses and reduce fat mass.