Background Inactivity Blunts Metabolic Adaptations to Intense Short-Term Training.

PURPOSE: This study determined if the level of background physical inactivity (steps per day) influences the acute and short-term adaptations to intense aerobic training. METHODS: Sixteen untrained participants (23.6 ± 1.7 yr) completed intense (80%-90% V˙O2peak) short-term training (5 bouts of exercise over 9 d) while taking either 4767 ± 377 steps per day (n = 8; low step) or 16,048 ± 725 steps per day (n = 8; high step). At baseline and after 1 d of acute exercise and then after the short-term training (posttraining), resting metabolic responses to a high-fat meal (i.e., plasma triglyceride concentration and fat oxidation) were assessed during a 6-h high-fat tolerance test. In addition, responses during submaximal exercise were recorded both before and after training during 15 min of cycling (~79% of pretraining V˙O2peak). RESULTS: High step displayed a reduced incremental area under the curve for postprandial plasma triglyceride concentrations by 31% after acute exercise and by 27% after short-term training compared with baseline (P < 0.05). This was accompanied by increased whole-body fat oxidation (24% and 19%; P < 0.05). Furthermore, stress during submaximal exercise as reflected by heart rate, blood lactate, and deoxygenated hemoglobin were all reduced in high step (P < 0.05), indicating classic training responses. Despite completing the same training regimen, low step showed no significant improvements in postprandial fat metabolism or any markers of stress during submaximal exercise after training (P > 0.05). However, the two groups showed a similar 7% increase in V˙O2peak (P < 0.05). CONCLUSION: When completing an intense short-term exercise training program, decreasing daily background steps from 16,000 to approximately 5000 steps per day blunts some of the classic cardiometabolic adaptations to training. The blunting might be more pronounced regarding metabolic factors (i.e., fat oxidation and blood lactate concentration) compared with cardiovascular factors (i.e., V˙O2peak).

Physiological responses to maximal 4 s sprint interval cycling using inertial loading: the influence of inter-sprint recovery duration.

PURPOSE: Interval exercise allows very high-power outputs to be maintained, a key for stimulating training adaptations. The main purpose of this study was to develop a sprint interval protocol that stimulated both anaerobic and aerobic systems while maximizing power output and minimizing fatigue. The secondary goal was to investigate the influence of inter-sprint recovery duration. METHODS: Sixteen (8 females) participants (age: 23.5 ± 3.4 years, peak oxygen consumption (VO2peak): 45.6 ± 9.2 ml kg-1 min-1) took part in this study. The exercise protocol involved 30 bouts of 4 s maximal cycling sprints using an 'Inertial Load Ergometer'. Recovery durations between sprints of 15, 30 and 45 s were studied in three trials. RESULTS: Peak power output (PPO) was maintained while taking 45 and 30 s of recovery, although it was 9% higher (p < 0.05) during 45 vs. 30 s. PPO with 15 s recovery declined 18% (p < 0.05) and then stabilized as did oxygen consumption (72±2% VO2peak) at a level that might reflect the peak rate of ATP-PC resynthesis from oxidative metabolism. The 15-, 30-, and 45 s trials elicited 72, 56, and 49% VO2peak and 86, 80, and 75% of maximal heart rate (all p<0.001). Perceived exertion increased with shorter recovery periods but remained at 12.6-14.7 and never became 'very hard'. CONCLUSION: The present study describes the use of an inertial-load ergometer to accommodate repeated 4 s maximal cycling sprints that elicit 72% VO2peak when the recovery period is 15 s. However, a recovery duration of 15 s was insufficient for the maintenance of power generation. TRIAL REGISTRATION NUMBER AND DATE: NCT04448925, 26 Jun 2020; retrospectively registered to clinicaltrials.gov.

Inertial Load Power Cycling Training Increases Muscle Mass and Aerobic Power in Older Adults.

PURPOSE: Reductions in skeletal muscle mass, beginning after the third decade of life, reduce maximal neuromuscular power (Pmax). Maximal aerobic power generation is also reduced. The primary purpose of this study was to investigate the effectiveness of maximal power cycling (PC) training using an inertial load ergometer on skeletal muscle mass and cardiovascular function in untrained 50- to 68-yr-old participants. METHODS: The study used a pre- or postoutcome exercise intervention testing untrained 50- to 68-yr-old adults (n = 39, M = 15, mean ± SE = 58.5 ± 0.8, range = 50-68 yr). Over the course of 8 wk, participants performed 15 min of training 3 times per week. Each session involved repeated (15-30 times) 4-s sprints of PC. Measurements were thigh muscle volume, total body lean mass, Pmax, peak oxygen consumption, cardio-ankle vascular index, performance on functional tests of living (FTLChair and FTLRamp), and intermuscular fat volume. RESULTS: Training for 8 wk increased thigh muscle volume (3.7% ± 0.9%, P < 0.001) and total body lean mass (1.5% ± 0.4%, P < 0.01) while increasing total body mass (TBM) (1.4% ± 0.3%, P < 0.01). Physical performance measures increased significantly (all P < 0.05) with improvements in Pmax (12.0% ± 1.5%); peak oxygen consumption (9.8% ± 1.8%), and FTL (8.5% ± 1.3% to 17.2% ± 2%). Cardio-ankle vascular index was significantly decreased -2.3% ± 1.1% (P < 0.05), indicating reduced arterial stiffness. CONCLUSIONS: These results demonstrate that 8 wk of PC training at true maximal power was effective at increasing muscle mass and maximal power, as well as maximal cardiovascular capacity and functional tasks in untrained 50- to 68-yr-olds.

Differences in joint power distribution in high and low lactate threshold cyclists.

PURPOSE: The biomechanical differences between cyclists with a high compared with a low blood lactate threshold (HLT; 80% VO2max vs LLT, 70% VO2max) have yet to be completely described. We hypothesize that HLT cyclists reduce the stress placed on the knee extensor muscles by increasing the relative contribution from the hip joint during high-intensity cycling. METHOD: Sixteen well-trained endurance athletes, with equally high VO2max while cycling and running completed submaximal tests during incremental exercise to identify lactate threshold ([Formula: see text]) while running and cycling. Subjects were separated into two groups based on % VO2max at LT during cycling (high; HLT: 80.2 ± 2.1% VO2max; n = 8) and (LLT: 70.3 ± 2.9% VO2max; n = 8; p < 0.01). Absolute and relative joint specific powers were calculated from kinematic and pedal forces using inverse dynamics while cycling at intensities ranging from 60-90% VO2max for between group comparisons. RESULT: There was no difference between HLT and LLT in [Formula: see text] (p > 0.05) while running. While cycling in LLT, knee joint absolute power increased with work rate (p < 0.05); however, in HLT no changes in knee joint absolute power occurred with increased work rate (p > 0.05). The HLT generated significantly greater relative hip power compared with the LLT group at 90% VO2max (p < 0.05). CONCLUSION: These data suggest that HLT cyclists exhibit a greater relative hip contribution to power output during cycling at 90% VO2max. These observations support the theory that lactate production during cycling can be reduced by spreading the work rate between various muscle groups.

Hourly 4-s Sprints Prevent Impairment of Postprandial Fat Metabolism from Inactivity.

High postprandial plasma lipids (PPL; i.e., triglycerides) are a risk factor for cardiovascular disease. Physical inactivity, characterized by prolonged sitting and a low step count, elevates PPL and thus risk of disease. PURPOSE: This study determined if the interruption of prolonged sitting (i.e., 8 h of inactivity) with hourly cycling sprints of only 4-s duration each (i.e., 4 s × 5 per hour × 8 h = 160 s·d SPRINTS) improves PPL. The 4-s sprints used an inertial load ergometer and were followed by 45 s of seated rest. METHODS: Four men and four women participated in two trials. Interventions consisted of an 8-h period of sitting (SIT), or a trial with equal sitting time interrupted with five SPRINTS every hour. The morning after the interventions, PPL and fat oxidation were measured over a 6-h period. Plasma glucose, insulin, and triglyceride concentrations were measured bihourly and incremental area under the curve (AUC) was calculated. RESULTS: No differences (P > 0.05) between interventions were found for plasma insulin or glucose AUC. However, SPRINTS displayed a 31% (408 ± 119 vs 593 ± 88 mg·dL per 6 h; P = 0.009) decrease in plasma triglyceride incremental AUC and a 43% increase in whole-body fat oxidation (P = 0.001) when compared with SIT. CONCLUSIONS: These data indicate that hourly very short bouts (4 s) of maximal intensity cycle sprints interrupting prolonged sitting can significantly lower the next day's postprandial plasma triglyceride response and increase fat oxidation after a high-fat meal in healthy young adults. Given that these improvements were elicited from only 160 s of nonfatiguing exercise per day, it raises the question as to what is the least amount of exercise that can acutely improve fat metabolism and other aspects of health.

Prolonged standing reduces fasting plasma triglyceride but does not influence postprandial metabolism compared to prolonged sitting.

Prolonged periods of sedentary behavior are linked to cardiometabolic disease independent of exercise and physical activity. This study examined the effects of posture by comparing one day of sitting (14.4 ± 0.3 h) to one day of standing (12.2 ± 0.1 h) on postprandial metabolism the following day. Eighteen subjects (9 men, 9 women; 24 ± 1 y) completed two trials (sit or stand) in a crossover design. The day after prolonged sitting or standing the subjects completed a postprandial high fat/glucose tolerance test, during which blood and expired gas was collected immediately before and hourly for 6 h after the ingestion of the test meal. Indirect calorimetry was used to measure substrate oxidation while plasma samples were analyzed for triglyceride, glucose, and insulin concentrations. Standing resulted in a lower fasting plasma triglyceride concentration (p = 0.021) which was primarily responsible for an 11.3% reduction in total area under the curve (p = 0.022) compared to sitting. However, no difference between trials in incremental area under the curve for plasma triglycerides was detected (p>0.05). There were no differences in substrate oxidation, plasma glucose concentration, or plasma insulin concentration (all p>0.05). These data demonstrate that 12 h of standing compared to 14 h of sitting has a small effect the next day by lowering fasting plasma triglyceride concentration, and this contributed to a 11.3% reduction in postprandial plasma triglyceride total area under the curve (p = 0.022) compared to sitting.

Inactivity induces resistance to the metabolic benefits following acute exercise.

Acute exercise improves postprandial lipemia, glucose tolerance, and insulin sensitivity, all of which are risk factors for cardiovascular disease. However, recent research suggests that prolonged sedentary behavior might abolish these healthy metabolic benefits. Accordingly, this study aimed to elucidate the impact of an acute bout of exercise on postprandial plasma triglyceride, glucose, and insulin concentrations after 4 days of prolonged sitting (~13.5 h/day). Ten untrained to recreationally active men (n = 5) and women (n = 5) completed a counterbalanced, crossover study. Four days of prolonged sitting without exercise (SIT) were compared with 4 days of prolonged sitting with a 1-h bout of treadmill exercise (SIT + EX; 63.1 ± 5.2% V̇o2max) on the evening of the fourth day. The following morning, participants completed a high-fat/glucose tolerance test (HFGTT), during which plasma was collected over a 6-h period and analyzed for triglycerides, glucose, and insulin. No differences between trials (P > 0.05) were found in the overall plasma triglyceride, glucose, or insulin responses during the HFGTT. This lack of difference between trials comes with similarly low physical activity (~3,500-4,000 steps/day) on each day except for the 1-h bout of exercise during SIT + EX the day before the HFGTT. These data indicate that physical inactivity (e.g., sitting ~13.5 h/day and <4,000 steps/day) creates a condition whereby people become "resistant" to the metabolic improvements that are typically derived from an acute bout of aerobic exercise (i.e., exercise resistance). NEW & NOTEWORTHY In people who are physically inactive and sitting for a majority of the day, a 1-h bout of vigorous exercise failed to improve lipid, glucose, and insulin metabolism measured the next day. It seems that something inherent to inactivity and/or prolonged sitting makes the body resistant to the 1 h of exercise preventing the normally derived metabolic improvements following exercise.

The Test-Retest Reliability of New Generation Power Indices of Wingate All-Out Test.

Although reliability correlations of traditional power indices of the Wingate test have been well documented, no study has analyzed new generation power indices based on milliseconds obtained from a Peak Bike. The purpose of this study was to investigate the retest reliability of new generation power indices. Thirty-two well-trained male athletes who were specialized in basketball, football, tennis, or track and field volunteered to take part in the study (age: 24.3 ± 2.2 years; body mass: 77 ± 8.3 kg; height: 180.3 ± 6.3 cm). Participants performed two Wingate all-out sessions on two separate days. Intra-class correlation coefficient (ICC), standard error measurement (SEM), smallest real differences (SRD) and coefficient of variation (CV) scores were analyzed based on the test and retest data. Reliability results of traditional power indices calculated based on 5-s means such as peak power, average power, power drop, and fatigue index ratio were similar with the previous findings in literature (ICC ≥ 0.94; CV ≤ 2.8%; SEM ≤ 12.28; SRD% ≤ 7.7%). New generation power indices such as peak power, average power, lowest power, power drop, fatigue index, power decline, maximum speed as rpm, and amount of total energy expenditure demonstrated high reliability (ICC ≥ 0.94; CV ≤ 4.3%; SEM ≤ 10.36; SRD% ≤ 8.8%). Time to peak power, time at maximum speed, and power at maximum speed showed a moderate level of reliability (ICC ≥ 0.73; CV ≤ 8.9%; SEM ≤ 63.01; SRD% ≤ 22.4%). The results of this study indicate that reliability correlations and SRD% of new generation power and fatigue-related indices are similar with traditional 5-s means. However, new time-related indices are very sensitive and moderately reliable.