Kristina L. Kendall

Bio: Kristina L. Kendall is an academic researcher from Edith Cowan University. The author has contributed to research in topics: High-intensity interval training & Interval training. The author has an hindex of 21, co-authored 70 publications receiving 1349 citations. Previous affiliations of Kristina L. Kendall include University of Oklahoma Health Sciences Center & United States Sports Academy.

Effects of β-alanine supplementation and high-intensity interval training on endurance performance and body composition in men; a double-blind trial

Abstract: Background: Intermittent bouts of high-intensity exercise result in diminished stores of energy substrates, followed by an accumulation of metabolites, promoting chronic physiological adaptations. In addition, β-alanine has been accepted has an effective physiological hydrogen ion (H + ) buffer. Concurrent high-intensity interval training (HIIT) and β-alanine supplementation may result in greater adaptations than HIIT alone. The purpose of the current study was to evaluate the effects of combining β-alanine supplementation with high-intensity interval training (HIIT) on endurance performance and aerobic metabolism in recreationally active college-aged men. Methods: Forty-six men (Age: 22.2 ± 2.7 yrs; Ht: 178.1 ± 7.4 cm; Wt: 78.7 ± 11.9; VO2peak: 3.3 ± 0.59 l·min-1) were assessed for peak O 2 utilization (VO 2 peak), time to fatigue (VO 2TTE ), ventilatory threshold (VT), and total work done at 110% of pre-training VO2peak (TWD). In a double-blind fashion, all subjects were randomly assigned into one either a placebo (PL – 16.5 g dextrose powder per packet; n = 18) or β-alanine (BA – 1.5 g β-alanine plus 15 g dextrose powder per packet; n = 18) group. All subjects supplemented four times per day (total of 6 g/day) for the first 21-days, followed by two times per day (3 g/day) for the subsequent 21 days, and engaged in a total of six weeks of HIIT training consisting of 5–6 bouts of a 2:1 minute cycling work to rest ratio. Results: Significant improvements in VO 2 peak, VO 2TTE , and TWD after three weeks of training were displayed (p < 0.05). Increases in VO 2 peak, VO 2TTE , TWD and lean body mass were only significant for the BA group after the second three weeks of training.

Ingesting a pre-workout supplement containing caffeine, B-vitamins, amino acids, creatine, and beta-alanine before exercise delays fatigue while improving reaction time and muscular endurance

Abstract: The purpose of this study was to determine the effects of the pre-workout supplement Assault™ (MusclePharm, Denver, CO, USA) on upper and lower body muscular endurance, aerobic and anaerobic capacity, and choice reaction time in recreationally-trained males. Subjective feelings of energy, fatigue, alertness, and focus were measured to examine associations between psychological factors and human performance. Twelve recreationally-trained males participated in a 3-week investigation (mean +/- SD, age: 28 +/- 5 y, height: 178 +/- 9 cm, weight: 79.2 +/- 15.7 kg, VO2max: 45.7 +/- 7.6 ml/kg/min). Subjects reported to the human performance laboratory on three separate occasions. All participants completed a baseline/familiarization day of testing that included a maximal graded exercise test for the determination of aerobic capacity (VO2max), one-rep maximum (1-RM) for bench and leg press to determine 75% of 1-RM, choice reaction tests, and intermittent critical velocity familiarization. Choice reaction tests included the following: single-step audio and visual, one-tower stationary protocol, two-tower lateral protocol, three-tower multi-directional protocol, and three-tower multi-directional protocol with martial arts sticks. Subjects were randomly assigned to ingest either the supplement (SUP) or the placebo (PL) during Visit 2. Subjects were provided with the cross-over treatment on the last testing visit. Testing occurred 20 min following ingestion of both treatments. Significant (p < 0.05) main effects for the SUP were observed for leg press (SUP: 13 ± 6 reps, PL: 11 ± 3 reps), perceived energy (SUP: 3.4 ± 0.9, PL: 3.1 ± 0.8), alertness (SUP: 4.0 ± 0.7, PL: 3.5 ± 0.8), focus (SUP: 4.1 ± 0.6, PL: 3.5 ± 0.8), choice reaction audio single-step (SUP: 0.92 ± 0.10 s, PL: 0.97 ± 0.11 s), choice reaction multi-direction 15 s (SUP: 1.07 ± 0.12 s, PL: 1.13 ± 0.14 s), and multi-direction for 30 s (SUP: 1.10 ± 0.11 s, PL: 1.14 ± 0.13 s). Ingesting the SUP before exercise significantly improved agility choice reaction performance and lower body muscular endurance, while increasing perceived energy and reducing subjective fatigue. These findings suggest that the SUP may delay fatigue during strenuous exercise.

The effects of a pre-workout supplement containing caffeine, creatine, and amino acids during three weeks of high-intensity exercise on aerobic and anaerobic performance

Abstract: A randomized, single-blinded, placebo-controlled, parallel design study was used to examine the effects of a pre-workout supplement combined with three weeks of high-intensity interval training (HIIT) on aerobic and anaerobic running performance, training volume, and body composition. Twenty-four moderately-trained recreational athletes (mean ± SD age = 21.1 ± 1.9 yrs; stature = 172.2 ± 8.7 cm; body mass = 66.2 ± 11.8 kg, VO2max = 3.21 ± 0.85 l·min-1, percent body fat = 19.0 ± 7.1%) were assigned to either the active supplement (GT, n = 13) or placebo (PL, n = 11) group. The active supplement (Game Time®, Corr-Jensen Laboratories Inc., Aurora, CO) was 18 g of powder, 40 kcals, and consisted of a proprietary blend including whey protein, cordyceps sinensis, creatine, citrulline, ginseng, and caffeine. The PL was also 18 g of powder, 40 kcals, and consisted of only maltodextrin, natural and artificial flavors and colors. Thirty minutes prior to all testing and training sessions, participants consumed their respective supplements mixed with 8-10 oz of water. Both groups participated in a three-week HIIT program three days per week, and testing was conducted before and after the training. Cardiovascular fitness (VO2max) was assessed using open circuit spirometry (Parvo-Medics TrueOne® 2400 Metabolic Measurement System, Sandy, UT) during graded exercise tests on a treadmill (Woodway, Pro Series, Waukesha, WI). Also, four high-speed runs to exhaustion were conducted at 110, 105, 100, and 90% of the treadmill velocity recorded during VO2max, and the distances achieved were plotted over the times-to-exhaustion. Linear regression was used to determine the slopes (critical velocity, CV) and y-intercepts (anaerobic running capacity, ARC) of these relationships to assess aerobic and anaerobic performances, respectively. Training volumes were tracked by summing the distances achieved during each training session for each subject. Percent body fat (%BF) and lean body mass (LBM) were assessed with air-displacement plethysmography (BOD POD®, Life Measurement, Inc., Concord, CA). Both GT and PL groups demonstrated a significant (p = 0.028) increase in VO2max from pre- to post-training resulting in a 10.3% and 2.9% improvement, respectively. CV increased (p = 0.036) for the GT group by 2.9%, while the PL group did not change (p = 0.256; 1.7% increase). ARC increased for the PL group by 22.9% and for the GT group by 10.6%. Training volume was 11.6% higher for the GT versus PL group (p = 0.041). %BF decreased from 19.3% to 16.1% for the GT group and decreased from 18.0% to 16.8% in the PL group (p = 0.178). LBM increased from 54.2 kg to 55.4 kg (p = 0.035) for the GT group and decreased from 52.9 kg to 52.4 kg in the PL group (p = 0.694). These results demonstrated improvements in VO2max, CV, and LBM when GT is combined with HIIT. Three weeks of HIIT alone also augmented anaerobic running performance, VO2max and body composition.

The effects of beta-alanine supplementation and high-intensity interval training on neuromuscular fatigue and muscle function

Abstract: The purpose of this study was to determine the effects of beta-alanine supplementation and high-intensity interval training (HIIT) on electromyographic fatigue threshold (EMGFT) and efficiency of electrical activity (EEA). A total of 46 men completed four, 2-min work bouts on a cycle ergometer. Using bipolar surface electrodes, the EMG amplitude was averaged and plotted over the 2-min. The resulting slopes were used to calculate EMGFT and EEA. Following initial testing, all participants were randomly assigned to either placebo (PL; n = 18), beta-alanine (BA; n = 18) or control groups (CON; n = 10). Following randomization, participants engaged in 6 weeks of HIIT training. Significant improvements in EMGFT and EEA resulted for both training groups. In conclusion, HIIT appeared to be the primary stimulus effecting EMGFT or EEA, suggesting adaptations from HIIT may be more influential than increasing skeletal muscle carnosine levels on delaying fatigue in recreationally active men.

Letter to the Editor: Standardized use of the terms "sedentary" and "sedentary behaviours"

Abstract: There has recently been an increase in research related to the health impact of sedentary behaviour (e.g., sitting) (Tremblay et al. 2010). Numerous studies suggest that those who engage in high amounts of sedentary behaviour can be at increased risk of morbidity and mortality regardless of their level of moderateto vigorous-intensity physical activity (MVPA) (Dunstan et al. 2010; Grøntved and Hu 2011; Katzmarzyk et al. 2009; Thorp et al. 2011; Wijndaele et al. 2011). Further, it has been noted that there is often little association between sedentary behaviour and MVPA (Biddle et al. 2004; Ekelund et al. 2006) and that it is possible for an individual to accumulate large amounts of both MVPA and sedentary behaviour in the course of a day (Healy et al. 2008; Katzmarzyk et al. 2009; Owen et al. 2010; Tremblay et al. 2010; Wong and Leatherdale 2008). Taken together, these findings suggest that too much sitting and too little MVPA represent separate and distinct risk factors for chronic, noncommunicable diseases (e.g., cardiovascular disease, diabetes, cancer). While research into the biology and health impact of sedentary behaviour represents an exciting new field of study, current inconsistencies in terminology are confusing for students, researchers, policymakers, and the general public. In short, the term “sedentary” currently has two separate and contradictory operational definitions. In this emerging field of research, sedentary behaviours are typically defined by both low energy expenditure (e.g., resting metabolic rate, typically ≤1.5 metabolic equivalents (METs)) and a sitting or reclining posture (Owen et al. 2010; Pate et al. 2008; Tremblay et al. 2010). In this context, a person may be described as sedentary if they engage in a large amount of sedentary behaviour. In contrast, in the sport and exercise literature the term sedentary is frequently used to describe the absence of some threshold of MVPA (Church et al. 2009; Melanson et al. 2009; Mullen et al. 2011; Sims et al. 2012; Smith et al. 2010). Thus, it is common for researchers in this field to describe a participant as sedentary because they are not meeting physical activity guidelines. Hence, many exercise studies include a “sedentary control group” or refer to their participants as coming from a “sedentary population” because of their lack of physical activity without actually measuring or assessing their level of sedentary behaviour. It is not difficult to see how these conflicting definitions of the term sedentary can easily lead to confusion. When reading the title or abstract of an article, it is often difficult to ascertain which definition of sedentary the authors have employed. If an article focuses on the health impact of a “sedentary lifestyle”, are they concerned with excessive sitting–lying down, the lack of physical activity, or both? Further, it is surprisingly common for articles within a given academic journal to oscillate between one definition and the other. To prevent further confusion, we propose that journal editors adopt a consistent definition of the term sedentary and require that all manuscripts published within their journal adhere to this common terminology. We suggest that journals formally define sedentary behaviour as any waking behaviour characterized by an energy expenditure ≤1.5 METs while in a sitting or reclining posture. In contrast, we suggest that authors use the term “inactive” to describe those who are performing insufficient amounts of MVPA (i.e., not meeting specified physical activity guidelines). The formal adoption of the above definitions by journal editors and reviewers would greatly improve the clarity of research and discussion related to these important health behaviours and help researchers searching for studies specific to sedentary behaviour or physical inactivity. We hope the research community will support these definitions and we look forward to further improvements in our understanding of the health impacts of sedentary behaviour and physical activity.

Prevalence of and interventions for sarcopenia in ageing adults: a systematic review. Report of the International Sarcopenia Initiative (EWGSOP and IWGS)

Abstract: OBJECTIVE: to examine the clinical evidence reporting the prevalence of sarcopenia and the effect of nutrition and exercise interventions from studies using the consensus definition of sarcopenia proposed by the European Working Group on Sarcopenia in Older People (EWGSOP).METHODS: PubMed and Dialog databases were searched (January 2000-October 2013) using pre-defined search terms. Prevalence studies and intervention studies investigating muscle mass plus strength or function outcome measures using the EWGSOP definition of sarcopenia, in well-defined populations of adults aged ≥50 years were selected.RESULTS: prevalence of sarcopenia was, with regional and age-related variations, 1-29% in community-dwelling populations, 14-33% in long-term care populations and 10% in the only acute hospital-care population examined. Moderate quality evidence suggests that exercise interventions improve muscle strength and physical performance. The results of nutrition interventions are equivocal due to the low number of studies and heterogeneous study design. Essential amino acid (EAA) supplements, including ∼2.5 g of leucine, and β-hydroxy β-methylbutyric acid (HMB) supplements, show some effects in improving muscle mass and function parameters. Protein supplements have not shown consistent benefits on muscle mass and function.CONCLUSION: prevalence of sarcopenia is substantial in most geriatric settings. Well-designed, standardised studies evaluating exercise or nutrition interventions are needed before treatment guidelines can be developed. Physicians should screen for sarcopenia in both community and geriatric settings, with diagnosis based on muscle mass and function. Supervised resistance exercise is recommended for individuals with sarcopenia. EAA (with leucine) and HMB may improve muscle outcomes.

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Effects of high-intensity interval training on cardiometabolic health: a systematic review and meta-analysis of intervention studies

Abstract: The current review clarifies the cardiometabolic health effects of high-intensity interval training (HIIT) in adults. A systematic search (PubMed) examining HIIT and cardiometabolic health markers was completed on 15 October 2015. Sixty-five intervention studies were included for review and the methodological quality of included studies was assessed using the Downs and Black score. Studies were classified by intervention duration and body mass index classification. Outcomes with at least 5 effect sizes were synthesised using a random-effects meta-analysis of the standardised mean difference (SMD) in cardiometabolic health markers (baseline to postintervention) using Review Manager 5.3. Short-term (ST) HIIT (<12 weeks) significantly improved maximal oxygen uptake (VO2 max; SMD 0.74, 95% CI 0.36 to 1.12; p<0.001), diastolic blood pressure (DBP; SMD −0.52, 95% CI −0.89 to −0.16; p<0.01) and fasting glucose (SMD −0.35, 95% CI −0.62 to −0.09; p<0.01) in overweight/obese populations. Long-term (LT) HIIT (≥12 weeks) significantly improved waist circumference (SMD −0.20, 95% CI −0.38 to −0.01; p<0.05), % body fat (SMD −0.40, 95% CI −0.74 to −0.06; p<0.05), VO2 max (SMD 1.20, 95% CI 0.57 to 1.83; p<0.001), resting heart rate (SMD −0.33, 95% CI −0.56 to −0.09; p<0.01), systolic blood pressure (SMD −0.35, 95% CI −0.60 to −0.09; p<0.01) and DBP (SMD −0.38, 95% CI −0.65 to −0.10; p<0.01) in overweight/obese populations. HIIT demonstrated no effect on insulin, lipid profile, C reactive protein or interleukin 6 in overweight/obese populations. In normal weight populations, ST-HIIT and LT-HIIT significantly improved VO2 max, but no other significant effects were observed. Current evidence suggests that ST-HIIT and LT-HIIT can increase VO2 max and improve some cardiometabolic risk factors in overweight/obese populations.