ABSTRACT:Kang, J, Ratamess, NA, Faigenbaum, AD, Bush, JA, Fardman, B, Vargas, A, Andriopoulos, T, Melao, J, O'Connell, E, Duff, A, Cmielewski, A, DeSalvo, J, Johnson, A, and Watts, M. Unlocking the body's clock: the role of exercise timing and chronotype in cardiometabolic responses. J Strength Cond Res 39(6): 634-641, 2025-Exercise enhances skeletal muscle metabolism and promotes overall health. However, the time-of-day effect of exercise on physiological responses in humans remains less clear. This study investigated how exercise timing and individual chronotype influence cardiorespiratory and metabolic responses during aerobic exercise. Thirty healthy, young (20.9 ± 1.5 years) adults comprising 15 men and 15 women were recruited and classified using the Morningness-Eveningness Questionnaire into morning types (M-types, n = 5), neither types (N-types, n = 20), and evening types (E-types, n = 5). All subjects underwent a V̇ o2 max test and 2 randomized exercise trials at ∼75% V̇ o2 max for 30 minutes, 1 in the morning before 9 am and 1 in the afternoon after 3 pm . Oxygen uptake (V̇ o2 ), heart rate (HR), respiratory exchange ratio (RER), and rates of carbohydrate (COX) and fat oxidation (FOX) were determined during the last 15 minutes of each exercise bout. No significant differences in V̇ o2 and HR were found between am and pm . However, RER and COX were lower ( p < 0.05) in am (0.920 ± 0.012 and 27.83 ± 2.29 mg·kg -1 ·min -1 , respectively) than pm (0.941 ± 0.09 and 30.65 ± 1.66 mg·kg -1 ·min -1 , respectively), while FOX was marginally higher ( p = 0.077) in am (4.12 ± 0.63 mg·kg -1 ·min -1 ) than pm (3.07 ± 0.49 mg·kg -1 ·min -1 ). In addition, HR was higher ( p < 0.05) in E-types (188.2 ± 3.9) than in N-types (178.4 ± 2.0) and M-types (167.7 ± 4.0). These results suggest that morning aerobic exercise may be more effective in mobilizing fat as an energy source compared with afternoon exercise. The similar V̇ o2 and HR levels between morning and afternoon sessions imply that the time of day may not have a major impact on cardiorespiratory responses during submaximal aerobic exercise. However, exercising HR seems to vary across chronotypes, highlighting the need to consider individual circadian phenotypes when conducting training programs.

The aim of this study was to compare the warm-up effects of a treadmill walking warm-up (TW) with a dynamic warm-up (DW) on the responses to cardiopulmonary exercise testing (CPET) in youth. A sample of 16 active youth (age 13.6 ± 1.8 yr) were tested for peak oxygen uptake (VO2 peak) using the Fitkids treadmill test protocol on 2 nonconsecutive days following different 6-min warm-up procedures. The TW consisted of walking on a treadmill at 2.2 mph and 0% grade whereas the DW consisted of 12 bodyweight exercises with a 2 kg medicine ball. Maximal heart rate (HR) was significantly higher following DW vs TW (200.8 ± 6.16 vs. 197.9 ± 7.3 bpm, respectively; p < 0.05), whereas no significant differences were found between DW and TW for VO2 peak (50.5 ± 9.9 vs 50.6 ± 11.1 ml/kg/min), maximal minute ventilation (VE; 93.0 ±21.4 vs. 92.7 ±21.2 L/min), maximal respiratory exchange ratio (1.19 ± 0.08 vs 1.22 ± 0.08), and total exercise test time (668.1 ± 103.5 vs 686.3 ± 97.0 s), respectively. During the Fitkids treadmill test protocol HR and VE were significantly higher following DW vs TW at stage 1, stage 2, stage 3 and stage 4, and oxygen uptake was significantly higher following DW vs TW during stage 1 (all p < 0.05). Findings indicate a DW elicits a higher maximal HR and higher submaximal HR, VE, and oxygen uptake values than TW during CPET in youth, although no differences in VO2 peak were observed.

Studies investigating the acute effect of postprandial exercise (PPE) on glucose responses exhibit significant heterogeneity in terms of participant demographic, exercise protocol, and exercise timing post-meal. As such, this study aimed to further analyze the existing literature on the impact of PPE on glycemic control in overweight individuals and individuals with obesity and type 2 diabetes (T2DM). A literature search was conducted through databases such as PubMed, CINAHL, and Google Scholar. Thirty-one original research studies that met the inclusion criteria were selected. A random-effect meta-analysis was performed to compare postprandial glucose area under the curve (AUC) and 24 h mean glucose levels between PPE and the time-matched no-exercise control (CON). Subgroup analyses were conducted to explore whether the glucose-lowering effect of PPE could be influenced by exercise duration, exercise timing post-meal, and the disease status of participants. This study revealed a significantly reduced glucose AUC (Hedges’ g = −0.317; SE = 0.057; p < 0.05) and 24 h mean glucose levels (Hedges’ g = −0.328; SE = 0.062; p < 0.05) following PPE compared to CON. The reduction in glucose AUC was greater (p < 0.05) following PPE lasting >30 min compared to ≤30 min. The reduction in 24 h mean glucose levels was also greater (p < 0.05) following PPE for ≥60 min compared to <60 min post-meal and in those with T2DM compared to those without T2DM. PPE offers a viable approach for glucose management and can be performed in various forms so long as exercise duration is sufficient. The glucose-lowering effect of PPE may be further enhanced by initiating it after the first hour post-meal. PPE is a promising strategy, particularly for patients with T2DM. This manuscript is registered with Research Registry (UIN: reviewregistry1693).

Abstract Kang, J, Ratamess, NA, Faigenbaum, AD, Bush, JA, Finnerty, C, DiFiore, M, Garcia, A, and Beller, N. Time-of-day effects of exercise on cardiorespiratory responses and endurance performance—A systematic review and meta-analysis. J Strength Cond Res 37(10): 2080–2090, 2023—The time-of-day effect of exercise on human function remains largely equivocal. Hence, this study aimed to further analyze the existing evidence concerning diurnal variations in cardiorespiratory responses and endurance performance using a meta-analytic approach. Literature search was conducted through databases, including PubMed, CINAHL, and Google Scholar. Article selection was made based on inclusion criteria concerning subjects' characteristics, exercise protocols, times of testing, and targeted dependent variables. Results on oxygen uptake (V̇o 2), heart rate (HR), respiratory exchange ratio, and endurance performance in the morning (AM) and late afternoon or evening (PM) were extracted from the chosen studies. Meta-analysis was conducted with the random-effects model. Thirty-one original research studies that met the inclusion criteria were selected. Meta-analysis revealed higher resting V̇o 2 (Hedges' g = −0.574; p = 0.040) and resting HR (Hedges' g = −1.058; p = 0.002) in PM than in AM. During exercise, although V̇o 2 remained indifferent between AM and PM, HR was higher in PM at submaximal (Hedges' g = −0.199; p = 0.046) and maximal (Hedges' g = −0.298; p = 0.001) levels. Endurance performance as measured by time-to-exhaustion or the total work accomplished was higher in PM than in AM (Hedges' g = −0.654; p = 0.001). Diurnal variations in V̇o 2 appear less detectable during aerobic exercise. The finding that exercising HR and endurance performance were greater in PM than in AM emphasizes the need to consider the effect of circadian rhythm when evaluating athletic performance or using HR as a criterion to assess fitness or monitor training.

ABSTRACT:Today's youth are weaker than previous generations, and measurable reductions in physical fitness are beginning to emerge. Without targeted initiatives that recognize the foundational importance of resistance training, weaker children and adolescents may be more likely to experience the inevitable consequences of neuromuscular dysfunction and less likely to experience the pleiotropic benefits of exercise and sport. Early exposure to strength-building activities is needed to prepare today's youth for ongoing participation in varied physical activities throughout this developmental phase of life. The novel iceberg of physical development is a metaphoric image that illustrates the sequential and cumulative influence of muscular strength on motor skills and physical abilities. Efforts to enhance the physical capacity of youth should include resistive skills that improve basic movement patterns and enhance motoric competence. A shift in our conceptual thinking about youth resistance training is needed to alter the current trajectory toward physical inactivity and related comorbidities.

The aim of this study was to compare the warm-up effects of treadmill walking (TW) with a dynamic (DY) bodyweight warm-up on maximal aerobic exercise performance in children. Sixteen children (10.9 ± 1.5 vrs) were tested for peak oxygen uptake (VO2 peak) on 2 nonconsecutive days following different 6 min warm-up protocols. TW consisted of walking on a motor-driven treadmill at 2.2 mph and 0% grade whereas the DY warm-up consisted of 9 body weight movements including dynamic stretches, lunges, and jumps. Maximal heart rate was significantly higher following DY than TW (193.9 ± 6.2 vs. 191.6 ± 6.1 bpm, respectively; p = 0.008). VO2 peak (54.8 ± 9.6 vs. 51.8 ± 8.7 mL/kg/min; p = 0.09), maximal minute ventilation (68.9 ± 14.8 vs. 64.9 ± 9.4 L/min; p = 0.27), maximal respiratory exchange ratio (1.12 ± 0.1 vs. 1.11 ± 0.1; p = 0.85) and total exercise time (614.0 ± 77.1 vs. 605 ± 95.0 s; p = 0.55) did not differ significantly between DY and TM warm-ups, respectively. These findings indicate that the design of the warm-up protocol can influence the heart rate response to maximal aerobic exercise and has a tendency to influence VO2 peak. A DY warm-up could be a viable alternative to a TW warm-up prior to maximal exercise testing in children.

Time restricted feeding (TRF) as a form of intermittent fasting (IF) has gained popularity because its ability to reduce body mass (BM) without an emphasis on caloric restriction. However, how this dietary protocol may affect health, fitness, and performance in a relatively healthy cohort remains less clear. The purpose of this article was to systematically review the current literature concerning the effect of TRF on anthropometric, metabolic, and fitness parameters in normal-weight adults and overweight and obese individuals. A systematic search of English literature was conducted through databases including PubMed, CINAHL, and Google Scholar. The search was facilitated by using various combinations of key words related to nutritional interventions, i.e., IF and TRF, and outcomes of interest, i.e., BM, body composition, glucose, insulin, lipid, fitness, and performance. The article selection was made based on the inclusion and exclusion criteria concerning the participants' characteristics, study design, intervention protocols, and targeted dependent variables. Twenty-three full-text longitudinal randomized and nonrandomized controlled studies were selected for this review. Our analysis indicates that TRF can reduce BM and improve nutrient metabolism in both normal- and over-weight individuals. TRF does not appear to alter protein synthesis and fat-free mass nor hamper aerobic fitness and muscular performance among physically active individuals including athletes. In conclusion, TRF as a more easily adaptable form of IF is a promising dietary approach to improving body composition and metabolic health while maintaining fitness and muscular function. However, more research is needed before this dietary protocol can be fully recommended for athletes especially those competing in sports that demand strength and power. Key teaching points and nutritional relevanceTime-restricted feeding (TRF) differs from other fasting protocols due to its emphasis on restricting eating window rather than caloric intake and can be more easily adopted by simply skipping a meal.Its deemphasis on caloric restriction appeals to many young and physically active individuals wanting to optimize body composition but needing sufficient energy to support their physical training and daily activity.Much of what is known regarding the impact of TRF on fitness and athletic performance was derived from studies that use the Ramadan fasting protocol, which differs from TRF in terms of protocol duration and feeding schedule.This review concludes that TRF is a promising dietary approach to improving body composition and metabolic health while maintaining fitness and muscular function in both normal- and over-weight individuals.Due to limited evidence concerning TRF and athletic performance, more research is needed before this dietary protocol can be fully recommended for athletes especially those competing in sports that demand strength and power.

Dynamic warm-up protocols (DWP) consisting of developmentally appropriate moderate- and high-intensity exercises have been found to influence the cardiopulmonary responses to maximal exercise in healthy children; however, the effects of a DWP on maximal treadmill exercise performance in adolescent runners are unclear. PURPOSE: To compare the effects of a DWP with a treadmill walking protocol (TWP) on maximal treadmill exercise performance in well-trained adolescent runners. METHODS: 12 male high school cross country runners (age 15.9 ± 1.0 yrs) performed a maximal exercise test with respiratory gas analysis on nonconsecutive days in random order following 2 different 6-min warm-up protocols. DWP consisted of 9 progressive bodyweight movements including lunges, hip bridges, and jumps whereas the TWP consisted of walking at 2.2 mph and 0% grade. The Fitkids treadmill test which consists of 90 sec stages and incremental increases in speed and grade was used for exercise testing. Comparisons between trials were made with a paired t-test. RESULTS: No significant differences between DWP and TWP trials were observed for peak oxygen uptake (62.1 ± 5.0 vs 62.5 ± 3.9 ml/kg/min, p = 0.40), maximal heart rate (195.2 ± 5.1 vs 194.1 ± 5.6 bpm, p = 0.23), maximal minute ventilation (118.7 ± 21.6 vs 117.9 ± 18.8 L/min, p = 0.42), maximal respiratory exchange ratio (1.13 ± 0.07 vs 1.15 ± 0.07, p = 0.23) and total exercise test time (780.5 ± 66.5 vs 798.0 ± 37.0 sec, p = 0.07), respectively. CONCLUSIONS: These preliminary findings suggest that the DWP used in this study does not influence the cardiopulmonary responses to maximal treadmill exercise in well-trained adolescent runners.

An equation that uses heart rate index (HRI) defined as HR/HRrest to predict oxygen uptake (VO2) in METs (e.g., METs = 6 × HRI - 5) has been developed retrospectively from aggregate data of 60 published studies. However, the prediction error of this model as used by an individual has not been established. Therefore, the purpose of this study was to examine the predictive validity of the HRI equation by comparing submaximal and maximal VO2 predicted by the equation (VO2-Pred) with that measured by indirect calorimetry (VO2-Meas). Sixty healthy adults (age 20.5 ± 2.4 yr., body mass 69.4 ± 13.4 kg, height 1.7 ± 0.1 m) underwent a VO2max test and an experimental trial consisting of a 15-min resting measurement and three successive 10-min treadmill exercise bouts performed at 40%, 60% and 80% of VO2max. VO2 and HR were recorded during both the submaximal and maximal exercises and used to obtain VO2-Pred and VO2-Meas for each intensity and for VO2max. Validation was carried out by paired t-test, regression analysis, and Bland-Altman plots. A modest but significant (p < 0.05) correlation was observed between VO2-Meas and VO2-Pred at 40% (r = 0.58), 60% (r = 0.53), and 80% of VO2max (r = 0.56) and at VO2max (r = 0.50). No differences between VO2-Pred and VO2-Meas were found at 40% (5.53 ± 1.21 vs. 5.28 ± 0.98 METs, respectively) of VO2max, but VO2-Pred was higher (p < 0.05) than VO2-Meas at 60% (8.42 ± 1.77 vs. 7.96 ± 1.39 METs, respectively) and 80% (10.79 ± 2.13 vs. 10.29 ± 1.81 METs, respectively) of VO2max. In contrast, VO2-Pred was lower (p < 0.05) than VO2-Meas at VO2max (12.32 ± 2.30 vs. 13.38 ± 2.24 METs, respectively). Standard errors of the estimate were 0.81, 1.20, 1.54, and 1.97 METs at 40%, 60%, 80% of VO2max and at VO2max, respectively. These results suggest that further investigation aimed to establish the accuracy of using HRI to predict VO2 is warranted.

Abstract Ketogenic diets (KDs) have received increasing attention among athletes and physically active individuals. However, the question as to whether and how the diet could benefit this healthy cohort remains unclear. Purpose: This study was designed to systematically review the existing evidence concerning the effect of KDs on body composition, aerobic and anaerobic capacity, muscle development, and sports performance in normal-weight individuals including athletes. Methods: A systematic search of English literature was conducted through electronic databases including PubMed, EBSCOhost, and Google Scholar. Upon the use of search criteria, 23 full-text original human studies involving non-obese participants were included in this review. For more stratified and focused analysis, these articles were further categorized based on the outcomes being examined including 1) body mass (BM) and %fat, 2) substrate utilization, 3) blood substrate and hormonal responses, 4) aerobic capacity and endurance performance, and 5) strength, power, and anaerobic capacity. Results: Our review indicates that a non-calorie-restricted KD carried out for ≥3 weeks can produce a modest reduction in BM and %fat, while maintaining fat-free mass. This diet leads to augmented use of fat as fuel, but this adaptation doesn’t seem to improve endurance performance. Additionally, ad libitum KDs combined with resistance training will pose no harm to developing strength and power, especially when protein intake is increased modestly. Conclusions: It appears that a non-calorie-restricted KD provides minimal ergogenic benefits in normal-weight individuals including athletes, but can be used for optimizing BM and body composition without compromising aerobic and anaerobic performance. Key teaching points Ketogenic diets have received increasing attention among athletes and physically active individuals. It remains elusive as to whether ketogenic diets could confer ergogenic benefits for those who are normal weight but want to use the diet to improve fitness and performance. An interesting dilemma exists in that ketogenic diets can reduce body mass and %fat and increase fat oxidation, but they can also decrease glycogen stores and limit sports performance. This review concludes that a non-calorie-restricted ketogenic diet provides minimal ergogenic benefits in normal-weight individuals, but can be used to optimize body mass and composition without compromising athletic performance. This finding can be important for esthetic or weight-sensitive athletes because the diet may allow them to reach a target body mass without having to sacrifice athletic performance. The ketogenic diet-induced metabolic adaptations require a state of ketosis, and thus caution should be taken because an excessive increase in ketone bodies can be detrimental to health.

Objective: The present study aimed to examine the interactive effect of exercise and energy balance on energy expenditure and substrate utilization. Method: Seven men and 7 women underwent three 2-day experimental protocols in a random order. Each protocol consisted of no exercise (NE), exercise only (EO), or exercise with a matched energy replacement (ER) on day 1 followed by metabolic testing that occurred after a 12-hour overnight fasting on day 2. Both EO and ER involved treadmill running at 60% maximal oxygen uptake (VO(2)max) that induced an energy expenditure of similar to 500 kcal. The replacement meal used in ER contained similar to 500 kcal made up of 45% carbohydrate, 30% fat, and 25% protein. During metabolic testing, oxygen uptake (VO2), heart rate (HR), respiratory exchange ratio (RER), and rates of carbohydrate (COX) and fat oxidation (FOX) were determined in three successive 15-minute periods including rest and exercise at 50% and 70% VO(2)max. Results: No differences in VO2 and HR were found at rest among NE, EO, and ER. However, RER was lower in EO than NE (0.840 +/- 0.014 vs 0.889 +/- 0.012, p < 0.05), COX (g center dot min(-1)) was lower in ER than NE (0.144 +/- 0.016 vs 0.197 +/- 0.019, p < 0.05), and FOX (g center dot min(-1)) was higher in EO or ER than NE (0.054 +/- 0.010 or 0.057 +/- 0.009 vs 0.034 +/- 0.007, p < 0.05). No treatment effects were observed for all variables at either intensity. Conclusions: This study demonstrates that an exercise of moderate intensity can increase resting fat oxidation even when the exercise-induced energy expenditure is balanced by energy intake. This finding suggests that muscle action is vital in augmenting fat utilization.

Integrative neuromuscular training (INT) has emerged as an effective strategy for improving health- and skill-related components of physical fitness, yet few studies have explored the cardiometabolic demands of this type of training in children. The aim of this study was to examine the acute cardiometabolic responses to a multi-modal INT protocol and to compare these responses to a bout of moderate-intensity treadmill (TM) walking in children. Participants (n = 14, age 10.7 ± 1.1 years) were tested for peak oxygen uptake (VO2) and peak heart rate (HR) on a maximal TM test and subsequently participated in two experimental conditions on nonconsecutive days: a 12-min INT protocol of six different exercises performed twice for 30 s with a 30 s rest interval between sets and exercises and a 12-min TM protocol of walking at 50% VO2peak. Throughout the INT protocol mean VO2 and HR increased significantly from 14.9 ± 3.6 mL∙kg−1∙min−1 (28.2% VO2 peak) to 34.0 ± 6.4 mL∙kg−1∙min−1 (64.3% VO2 peak) and from 121.1 ± 9.0 bpm (61.0% HR peak) to 183.5 ± 7.9 bpm (92.4% HR peak), respectively. While mean VO2 for the entire protocol did not differ between INT and TM, mean VO2 and HR during selected INT exercises and mean HR for the entire INT protocol were significantly higher than TM (all Ps ≤ 0.05). These findings suggest that INT can pose a moderate to vigorous cardiometabolic stimulus in children and selected INT exercises can be equal to or more metabolically challenging than TM walking.

It has been well documented that exercise of sufficient energy expenditure can elicit an increase in fat oxidation that persists following exercise. However, whether and how this exercise-induced metabolic benefit would be affected by replacing the energy expended during exercise remains unclear. PURPOSE: To compare energy expenditure and substrate utilization between exercise with and without energy replacement at rest and during exercise. METHODS: Fourteen healthy and recreationally trained subjects including 7 men and 7 women volunteered to participate in this study. Each subject underwent three 2-day experimental protocols in a random order. Each protocol consisted of no exercise (NE), exercise only (EO), or exercise with energy replacement (ER) on day 1 that was followed by metabolic assessment that took place in a fasted condition on day 2. The exercise in EO and ER was a treadmill running at 60% VO2max that induced an energy expenditure of 500 kilocalories. The replacement meal used in ER contained 500 kilocalories made up by 45% carbohydrate, 30% fat, and 25% protein. During the metabolic assessment, oxygen uptake (VO2), heart rate (HR), respiratory exchange ratio (RER), and rates of carbohydrate (COX) and fat oxidation (FOX) were determined in three successive 10-min periods that included rest, exercise at 50% VO2max and exercise at 70% VO2max. RESULTS: No differences in VO2 and HR were found at rest between NE, EO, and ER. However, RER was lower in EO than NE (0.840±0.014 vs. 0.889±0.012, p<0.05), COX (g∙min-1) was lower in ER than NE (0.144±0.016 vs. 0.197±0.019, p<0.05), and FOX (g∙min-1) was higher in either EO or ER than NE (0.054±0.010 or 0.057±0.009 vs. 0.034±0.007, p<0.05). When these variables were compared under the exercise conditions, no treatment effects were noted for all variables at either intensity. CONCLUSION: Our results demonstrate that an acute bout of aerobic exercise can elicit an increase in fat oxidation even when the exercise-induced energy deficit is replaced by energy intake. These findings suggest that factors other than caloric deficit mediate the exercise-induced lipolytic effect.

The purpose of this study was to examine acute hematological and mood perception responses to supplementation with p‐synephrine alone and in combination with caffeine during quiet sitting. Sixteen subjects visited the laboratory on 6 occasions and were given (in randomized double‐blind manner) 103‐mg p‐synephrine (S), 233‐mg caffeine + 104‐mg p‐synephrine, 240‐mg caffeine, 337‐mg caffeine + 46‐mg p‐synephrine, 325‐mg caffeine, or a placebo (PL). The subjects sat quietly for 3 hr while completing mood state questionnaires every 30 min. Venous blood samples were collected at baseline (pre) and 3 hr (post) to determine immune, lipid, and chemistry panels. Compared with PL, no significant supplement differences were observed during the S trial with the exception of differential time effects seen in hematocrit (decrease in PL, no change in S), triglycerides and very low‐density lipoproteins (no changes in PL, significant decreases in S), and iron (no change in PL, significant elevation in S). Supplements containing caffeine showed increased feelings of attention, excitement, energy, and vigor. These data indicate that consumption of 103‐mg p‐synephrine does not negatively impact acute blood parameters, does not augment the effects of caffeine, or produce stimulant‐like perceptual mood effects.

This investigation examined the interactive effect of body-weight (BW) exercises and vibration on cardiometabolic responses. Fourteen subjects performed a BW exercise protocol with (BW+V) and without (BW‒V) vibration in a randomized order. The BW exercise protocol consisted of three circuits of eight calisthenics-based exercises including prisoner squat, push-up, isometric squat, reverse dip, lunge, flutter kicks, isometric lunge, and T push-up. Vibratory frequency and amplitude were set at 40 Hz and 4 mm, respectively. Oxygen uptake (VO2), heart rate (HR), expired ventilation (VE), and blood lactate [La] were determined during the protocol and 30-minute recovery. The mean VO2 reached 48% and 50% of VO2max and the mean HR reached 80% and 83% of HRmax in BW‒V and BW+V, respectively. During the protocol, while the mean VE was greater (p=.031) in BW+V than BW‒V, no differences were seen for VO2 and HR between the two conditions. During recovery, while mean VO2 was greater (p=.002) in BW+V than BW-V, no differences were seen for VE and HR between the two conditions. [La] values were significantly elevated but remained similar between the two conditions. Exercise-specific VO2 was higher during the prisoner squat (p=.003) and isometric squat (p=.042) in BW+V than BW‒V, while no differences in VO2 were observed for all other exercises. Performing three circuits of eight BW exercises in a rapid-and-intense manner produced a sufficient increase in cardiometabolic responses. Metabolic potentiation associated with combining vibration with BW exercises seemed to be influenced by how the exercises were carried out on a vibration plate.

Medicine ball interval training (MBIT) has been found to be an effective exercise modality in fitness programs, yet the acute physiological responses to this type of this exercise in youth are unknown. The purpose of this study was to examine the acute cardiometabolic responses to MBIT in children. Fourteen children (mean age 10.1 ± 1.3 yr) were tested for peak oxygen uptake (VO2peak) on a treadmill and subsequently (> 48 hours later) performed a progressive 10 min MBIT protocol of 5 exercises (EX): standing marches (EX1), alternating lunges (EX2), squat swings (EX3), chest passes (EX4) and double arm slams (EX5). A 2.3 kg medicine ball was used for all trials and each exercise was performed twice for 30 sec with a 30 sec rest interval between sets and exercises. Participants exercised while connected to a metabolic system and heart rate (HR) monitor. During the MBIT protocol, mean HR significantly (p<0.05, η2 = 0.89) increased from 121.5 ± 12.3 bpm during EX1 to 178.3 ± 9.4 bpm during EX5 and mean VO2 significantly (p<0.05, η2= 0.88) increased from 15.5 ± 2.9 ml × kg-1 × min-1 during EX1 to 34.9 ± 5.1 ml × kg-1 × min-1during EX5. Mean HR and VO2 values during MBIT ranged from 61.1% to 89.6% of HRpeak and from 28.2% to 63.5% of VO2peak. These descriptive data indicate that MBIT can pose a moderate to vigorous cardiometabolic stimulus in children.

The purpose was to examine cardiovascular responses to supplementation with p-synephrine alone and in combination with caffeine during quiet sitting. Sixteen subjects were given (in double-blind manner) either 103mg of p-synephrine (S), 233mg of caffeine +104mg of p-synephrine (LC+S), 240mg of caffeine (LC), 337mg of caffeine +46mg of p-synephrine (HC+S), 325mg of caffeine (HC), or a placebo. The subjects sat quietly for 3hr while heart rate (HR) and blood pressure were measured. Only HC+S and HC significantly increased mean systolic blood pressure (SBP) during the second hour and tended to increase mean SBP during the third hour. Mean diastolic blood pressure in S was significantly lower than the other trials during the first and second hours, and mean arterial pressure was significantly lower in S compared to the LC, LC+S, HC, and HC+S trials. No differences were observed in HR. Consumption of p-synephrine may acutely reduce diastolic blood pressure and mean arterial pressure and not affect SBP or HR during quiet sitting. The addition of p-synephrine to caffeine did not augment SBP or HR indicating that consumption of up to 104mg of p-synephrine does not induce cardiovascular stress during quiet sitting.

Faigenbaum, AD, Kang, J, Ratamess, NA, Farrell, A, Golda, S, Stranieri, A, Coe, J, and Bush, JA. Acute cardiometabolic responses to a novel training rope protocol in children. J Strength Cond Res 32(5): 1197-1206, 2018-The purpose of this study was to quantify the acute cardiometabolic responses to a novel training rope (TR) protocol in children. Fifteen boys (10.6 ± 1.4 years) were tested for peak oxygen uptake (V[Combining Dot Above]O2) on a treadmill and subsequently (2-7 days later) performed a progressive 10-minute protocol of 5 TR exercises (EX): EX1: standing side-to-side waves, EX2: seated alternating waves, EX3: standing alternating waves, EX4: jumping jacks, and EX5: double-arm slams. Participants performed 2 sets of each TR exercise for 30 seconds per set with a 30-second rest interval between sets and exercises. A 12.8-m TR (4.1 kg) was used for all trials, and a metronome was used to standardize cadence. Peak values for V[Combining Dot Above]O2 and HR during the treadmill test were 47.4 ± 8.8 ml·kg·min and 195.1 ± 6.6 b·min, respectively. During the TR protocol, mean V[Combining Dot Above]O2 and HR significantly increased (p ≤ 0.05) from set 1 of EX1 (10.3 ± 2.6 ml·kg·min and 103.2 ± 11.6 b·min, respectively) to set 2 of EX5 (30.0 ± 3.9 ml·kg·min and 168.6 ± 11.8 b·min, respectively). Percentage of peak V[Combining Dot Above]O2 and peak HR values attained during the TR protocol ranged from 21.5 to 64.8% and from 52.9 to 86.4%, respectively. These descriptive data indicate that TR exercise can pose a moderate to vigorous cardiometabolic stimulus in children and with proper supervision and instruction may serve as a worthwhile complement to youth fitness programs.