Systemic and muscular responses to effort-matched short intervals and long intervals in elite cyclists

Multiple Short Intervals Induce Longer Time Above 90% of Maximal Oxygen Consumption Than Long Intervals When Matched by Similar Fixed Intensity, But Not During Self-Paced Cycling Ergometry

In previous studies comparing different interval protocols for high-intensity interval training, large differences in time above 90% of maximal oxygen consumption (V˙O2max) have been observed. Differences can possibly be attributed to session design or intensity control. Twelve well-trained cyclists and triathletes (V˙O2max: 68 [6.3] mL·min-1·kg-1) performed 2 different cycling ergometry interval protocols of 3 × 13 × 30/15 seconds (short interval [SI]) and 6 × 5 minutes (long interval [LI]), each with a fixed intensity based on percentages of maximal aerobic power and self-paced approach with maximal effort. The time above 90%V˙O2max was significantly greater for SI than LI in fixed (P < .01) but not in self-paced intensity (P = .321). All physiological parameters assessed and power outputs were higher in self-paced than fixed (all P < .001; all ηp2>.795), resulting in an increased time above 90%V˙O2max for SI (1130 [204] vs 420 [259] s) and LI (1016 [312] vs 178 [159] s). When the short recovery periods are included in total interval work duration in SI, and SI and LI are matched on duration and fixed intensities (similar percentage of maximal aerobic power), SI gave greater time above 90%V˙O2max. However, when SI and LI were performed with the self-paced approach and maximal effort, the exercise intensity became higher and there were no differences in time above 90%V˙O2max.

A microcycle of high-intensity short-interval sessions induces improvements in indicators of endurance performance compared to regular training

The purpose of this study was to evaluate the effects of a microcycle of high-intensity interval training (HIT) sessions with multiple short work intervals followed by an active recovery period, compared to a similar duration of regular training, on determinants and indicators of endurance performance in well-trained cyclists. The participants in the BLOCK group performed a 6-day HIT microcycle including five HIT sessions (5 × 8.75-min 30/15 s short intervals) followed by a 6-day active recovery period with reduced training load, while the regular training group (REG) performed 12 days of their regular training, including four HIT sessions. Physiological testing was performed before and after the training periods. From pre- to post- intervention, BLOCK demonstrated significantly larger improvements than REG in mean power output (PO) during the last min of the maximal oxygen uptake (VO2max) test (POVO2max) (3.7 vs. 0.7%, p = 0.009, and effect size (ES) = 1.00) and mean PO during the 10-s sprint (2.8 vs. 1.9%, p = 0.028, and ES = 0.63). No significant differences between BLOCK and REG were observed for VO2max, PO at 4 mmol·L-1 [blood lactate] (PO4mmol), 15-min maximal mean power output (PO15-min), and gross efficiency (p = 0.156-0.919). However, there was a tendency for larger improvements in the performance index (calculated from the main performance indicators POVO2max, PO4mmol, and PO15-min) in BLOCK compared to REG (2.9% vs. 1.2%, p = 0.079, and ES = 0.71). A 6-day high-intensity short-interval microcycle followed by a 6-day active recovery period induces improvements in endurance performance indicators compared to regular training, demonstrating its potential as an efficient strategy for endurance training in well-trained cyclists.

The higher oxygen consumption during multiple short intervals is sex-independent and not influenced by skeletal muscle characteristics in well-trained cyclists

It has been suggested that time spent at a high fraction of maximal oxygen consumption (%V ˙ $\dot{\mathrm{V}}$ O2max) plays a decisive role for adaptations to interval training. However, previous studies examining how interval sessions should be designed to achieve a high %V ˙ $\dot{\mathrm{V}}$ O2max have exclusively been performed in males. The present study compared the %V ˙ $\dot{\mathrm{V}}$ O2max attained during three different 6 × 8 min interval protocols, in female (n = 11;V ˙ $\dot{\mathrm{V}}$ O2max, 62.5 (6.4) mL · min-1·kg-1) and male (n = 8;V ˙ $\dot{\mathrm{V}}$ O2max, 81.0 (5.2) mL · min-1·kg-1) cyclists. Mean power output during work intervals were identical across the three interval protocols, corresponding to the cyclist's 40 min maximal effort (PO40min): (1) 30 s intervals at 118% of PO40min interspersed with 15 s active recovery at 60% (30/15), (2) constant pace at 100% of PO40min (CON), and (3) altering between 60 s intervals at 110% and 60 s at 90% of PO40min (60/60). Additionally, the study explored whether the m. vastus lateralis characteristics of the cyclists (fiber type proportion, capillarization, and citrate synthase activity) were associated with the %V ˙ $\dot{\mathrm{V}}$ O2max attained during the interval sessions. Overall, mean %V ˙ $\dot{\mathrm{V}}$ O2max and time ≥90% ofV ˙ $\dot{\mathrm{V}}$ O2max were higher during 30/15 compared to CON (86.7 (10.1)% and 1123 (787) s versus 85.0 (10.4)% and 879 (779) s, respectively; both p ≤ 0.01) and 60/60 (85.6 (10.0)% and 917 (745) s, respectively; both p ≤ 0.05), while no difference was observed between 60/60 and CON (both p ≥ 0.36). During interval sessions, %V ˙ $\dot{\mathrm{V}}$ O2max and time ≥90% ofV ˙ $\dot{\mathrm{V}}$ O2max did not differ between sexes. Skeletal muscle characteristics were not related to %V ˙ $\dot{\mathrm{V}}$ O2max during interval sessions. In conclusion, well-trained cyclists demonstrate highest %V ˙ $\dot{\mathrm{V}}$ O2max during 30/15, irrespective of sex and skeletal muscle characteristics.

The higher the fraction of maximal oxygen uptake is during interval training, the greater is the cycling performance gain

It has been suggested that time at a high fraction (%) of maximal oxygen uptake (VO2max) plays a decisive role for adaptations to interval training. Yet, no study has, to date, measured the % of VO2max during all interval sessions throughout a prolonged training intervention and subsequently related it to the magnitude of training adaptations. Thus, the present study aimed to investigate the relationship between % of VO2max achieved during an interval training intervention and changes in endurance performance and its physiological determinants in well-trained cyclists. Twenty-two cyclists (VO2max 67.1 (6.4) mL·min-1 ·kg-1; males, n = 19; females, n = 3) underwent a 9-week interval training intervention, consisting 21 sessions of 5 × 8-min intervals conducted at their 40-min highest sustainable mean power output (PO). Oxygen uptake was measured during all interval sessions, and the relationship between % of VO2max during work intervals and training adaptations were investigated using linear regression. A performance index was calculated from several performance measures. With higher % of VO2max during work intervals, greater improvements were observed for maximal PO during the VO2max test (R2 adjusted = 0.44, p = 0.009), PO at 4 mmol·L-1 [blood lactate] (R2 adjusted = 0.25, p = 0.035), the performance index (R2 adjusted = 0.36, p = 0.013), and VO2max (R2 adjusted = 0.54, p = 0.029). Other measures, such as % of maximal heart rate, were related to fewer outcome variables and exhibited poorer session-to-session repeatability compared to % of VO2max. In conclusion, improvements in endurance measures were positively related to the % of VO2max achieved during interval training. Percentage of VO2max was the measure that best reflected the magnitude of training adaptations.

A narrative review exploring advances in interval training for endurance athletes

Interval training is considered an essential training component in endurance athletes. Recently, there has been a focus on optimization of interval training characteristics to sustain a high fraction of maximal oxygen consumption (≥90% VO2max) to improve physiological adaptations and performance. Herein, we present a synopsis of the latest research exploring both acute and chronic studies in endurance athletes. Further, a decision flowchart was created for athletes and coaches to select the most appropriate interval training regime for specific individualized goals.

Prescription of High-intensity Aerobic Interval Training Based on Oxygen Uptake Kinetics

Endurance training results in diverse adaptations that lead to increased performance and health benefits. A commonly measured training response is the analysis of oxygen uptake kinetics, representing the demand of a determined load (speed/work) on the cardiovascular, respiratory, and metabolic systems, providing useful information for the prescription of constant load or interval-type aerobic exercise. There is evidence that during high-intensity aerobic exercise some interventions prescribe brief interval times (<1-min), which may lead to a dissociation between the load prescribed and the oxygen uptake demanded, potentially affecting training outcomes. Therefore, this review explored the time to achieve a close association between the speed/work prescribed and the oxygen uptake demanded after the onset of high-intensity aerobic exercise. The evidence assessed revealed that at least 80% of the oxygen uptake amplitude is reached when phase II of oxygen uptake kinetics is completed (1 to 2 minutes after the onset of exercise, depending on the training status). We propose that the minimum work-time during high-intensity aerobic interval training sessions should be at least 1 minute for athletes and 2 minutes for non-athletes. This suggestion could be used by coaches, physical trainers, clinicians and sports or health scientists for the prescription of high-intensity aerobic interval training.

Adding Intermittent Vibration to Varied-intensity Work Intervals: No Extra Benefit

Varied-intensity work intervals have been shown to induce higher fractions of maximal oxygen uptake during high-intensity interval training compared with constant-intensity work intervals. We assessed whether varied-intensity work intervals combined with intermittent vibration could further increase cyclists' fraction of maximal oxygen uptake to potentially optimise adaptive stimulus. Thirteen cyclists (V̇O_2max: 69.7±7.1 ml·kg^-1·min^-1) underwent a performance assessment and two high-intensity interval training sessions. Both comprised six 5-minute varied-intensity work intervals within which the work rate was alternated between 100% (3×30-second blocks, with or without vibration) and 77% of maximal aerobic power (always without vibration). Adding vibration to varied-intensity work intervals did not elicit a longer time above ninety percent of maximal oxygen uptake (415±221 versus 399±209 seconds, P=0.69). Heart rate- and perceptual-based training-load metrics were also not affected (all P≥0.59). When considering individual work intervals, no between-condition differences were found (fraction of maximal oxygen uptake, P=0.34; total oxygen uptake, P=0.053; mean minute ventilation, P=0.079; mean heart rate, P=0.88; blood lactate concentration, P=0.53; ratings of perceived exertion, P=0.29). Adding intermittent vibration to varied-intensity work intervals does not increase the fraction of maximal oxygen uptake elicited. Whether intermittent exposure to vibration can enhance cyclists' adaptive stimulus triggered by high-intensity interval training remains to be determined.

The Skeletal Muscle Microbiopsy Method in Exercise and Sports Science Research: A Narrative and Methodological Review

BACKGROUND

The skeletal muscle microbiopsy protocol was introduced to the Exercise and Sports Science (ESS) research field in 1999 and has been used as a protocol to directly examine muscular structural and biochemical changes. There is much variation in the reporting of the microbiopsy protocol and its related pre-and post-procedure for participant care and sample collection. The purpose of this narrative and methodological review is to compare the microbiopsy to the traditional Bergström protocol used in the ESS field, identify and summarize all related microbiopsy protocols used in previous ESS studies and determine the most frequently used microbiopsy protocols aspects and associated pre- and post-biopsy procedures; METHODS: A review of literature up to January, 2022 was used following the PRISMA and Cochrane Methodological Review Guide to determine frequently used methods that may facilitate optimal and potential recommendations for muscle microbiopsy needle gauge (G), concentration or dose (% or mL) and administration of local anesthetic, co-axial/cannula introducer gauge (G), muscle depth (cm), muscle sample size collected (mg), passes to collect samples, time points of muscle sampling, and promotion of participant compliance and minimization of adverse events; RESULTS: 85 articles were selected based on the inclusionary requirements related to the ESS field or methodological considerations. The most frequently reported aspects in previous research to suggest the location of the vastus lateralis is the midpoint between the patella and the greater trochanter of the femur or 1/3 or 2/3 the distance from the patella to anterior superior iliac spine, 14 G biopsy needle, subcutaneous injected lidocaine administration (2 mL; 1%), 13 G co-axial/cannula, 1-2 cm muscle depth, 10-20 mg of muscle sample, ~3-time points, 2-3 passes; DISCUSSION: There is much variation in the reporting of the microbiopsy protocol and its related pre-and post-biopsy procedures. Standardization in reporting may promote recommendations to optimize data integrity, participant safety, participant adherence to the study design, and increase reproducibility. Recommendations are made for the microbiopsy procedure based on frequently reported characteristics.

Physiological and Psychological Responses to Three Distinct Exercise Training Regimens Performed in an Outdoor Setting: Acute and Delayed Response

The aim of this study was to compare the acute responses to three time-matched exercise regimens. Ten trained adults (age, maximum oxygen consumption (VO2max), and body mass index (BMI) = 25.9 ± 5.6 yr, 50.9 ± 5.4 mL·kg-1·min-1, and 22.1 ± 1.8 kg·m-2) completed sprint interval training (SIT) requiring 14 × 5 s efforts with 35 s of recovery, high-intensity interval training (HIIT) consisting of 18 × 15 s efforts at ~90% of peak heart rate (HRpeak) with 15 s of recovery, and vigorous continuous training (CT) consisting of 8.75 min at ~85 %HRpeak, in randomized order. Heart rate, blood lactate concentration, rating of perceived exertion, affective valence, and enjoyment were monitored. Moreover, indices of neuromuscular function, autonomic balance, diet, mental stress, incidental physical activity (PA), and sleep were measured 24 h after each session to analyze the magnitude of recovery. Both HIIT and CT exhibited a greater %HRpeak and time ≥ 90 %HRpeak than SIT (p < 0.05). Blood lactate and rating of perceived exertion were higher in response to SIT and HIIT vs. CT (p < 0.05); however, there were no differences in enjoyment (p > 0.05). No differences were exhibited in any variable assessed along 24 h post-exercise between conditions (p > 0.05). These data suggest that HIIT and CT accumulate the longest duration at near maximal intensities, which is considered a key factor to enhance VO2max.

Acute Effects of Work Rest Interval Duration of 3 HIIT Protocols on Cycling Power in Trained Young Adults

High-Intensity Interval Training (HIIT) is described as a succession of short duration and maximum or near-maximum intensity efforts, alternated by recovery periods during which exercise continues at a lower intensity (active recovery) or is interrupted (passive recovery). Our objective was to evaluate the acute responses of three HIIT protocols of different work/rest interval times over the total time of the session, with self-selectable load and up to exhaustion, “all out”.The sample was composed of 22 male participants (n = 22) between 19 and 24 years old. The HIIT protocol consisted of one of the three HIIT protocols, of 30, 60 and 90 s density ratio 1:1 and with passive rest, with a total exercise duration of 10 min. The test was performed in a cycloergometer set in workload mode independent of the pedaling frequency. The comparison of the three HIIT protocols shows that the duration of the work/rest intervals, starting from 30 s of work, in the cycloergometer, there are no significant differences in the levels of lactate concentration in the blood, nor in the heart rate, since a similar amount is obtained in the three protocols. The percentage of maximum power developed reached in each HIIT protocol is related to the duration of the working intervals.

Superior Physiological Adaptations After a Microcycle of Short Intervals Versus Long Intervals in Cyclists

PURPOSE

To compare the effects of a 1-week high-intensity aerobic-training shock microcycle composed of either 5 short-interval sessions (SI; n = 9, 5 series with 12 × 30-s work intervals interspersed with 15-s recovery and 3-min recovery between series) or 5 long-interval sessions (LI; n = 8, 6 series of 5-min work intervals with 2.5-min recovery between series) on indicators of endurance performance in well-trained cyclists.

METHODS

Before and following 6 days with standardized training loads after the 1-week high-intensity aerobic-training shock microcycle, both groups were tested in physiological determinants of endurance performance.

RESULTS

From pretraining to posttraining, SI achieved a larger improvement than LI in maximal oxygen uptake (5.7%; 95% confidence interval, 1.3-10.3; P = .015) and power output at a blood lactate concentration of 4 mmol·L-1 (3.8%; 95% confidence interval, 0.2-7.4; P = .038). There were no group differences in changes of fractional use of maximal oxygen uptake at a workload corresponding to a blood lactate concentration of 4 mmol·L-1, gross efficiency, or the 1-minute peak power output from the maximal-oxygen-uptake test.

CONCLUSION

The SI protocol may induce superior changes in indicators of endurance performance compared with the LI protocol, indicating that SI can be a good strategy during a 1-week high-intensity aerobic-training shock microcycle in well-trained cyclists.

Effects of including sprints during prolonged cycling on hormonal and muscular responses and recovery in elite cyclists

This study investigated the acute effects of including 30‐second sprints during prolonged low‐intensity cycling on muscular and hormonal responses and recovery in elite cyclists. Twelve male cyclists (VO_2max, 73.4 ± 4.0 mL/kg/min) completed a randomized crossover protocol, wherein 4 hours of cycling at 50% of VO_2max were performed with and without inclusion of three sets of 3 × 30 seconds maximal sprints (E&S vs E, work‐matched). Muscle biopsies (m. vastus lateralis) and blood were sampled at Pre, immediately after (Post) and 3 hours after (3 h) finalizing sessions. E&S led to greater increases in mRNA levels compared with E for markers of fat metabolism (PDK4, Δ‐Log2 fold change between E&S and E ± 95%CI Post; 2.1 ± 0.9, Δ3h; 1.3 ± 0.7) and angiogenesis (VEGFA, Δ3h; 0.3 ± 0.3), and greater changes in markers of muscle protein turnover (myostatin, ΔPost; −1.4 ± 1.2, Δ3h; −1.3 ± 1.3; MuRF1, ΔPost; 1.5 ± 1.2, all P < .05). E&S showed decreased mRNA levels for markers of ion transport at 3h (Na⁺‐K⁺ α1; −0.6 ± 0.6, CLC1; −1.0 ± 0.8 and NHE1; −0.3 ± 0.2, all P < .05) and blunted responses for a marker of mitochondrial biogenesis (PGC‐1α, Post; −0.3 ± 0.3, 3h; −0.4 ± 0.3, P < .05) compared with EE&S and E showed similar endocrine responses, with exceptions of GH and SHBG, where E&S displayed lower responses at Post (GH; −4.1 ± 3.2 μg/L, SHBG; −2.2 ± 1.9 nmol/L, P < .05). Both E&S and E demonstrated complete recovery in isokinetic knee extension torque 24 hours after exercise. In conclusion, we demonstrate E&S to be an effective exercise protocol for elite cyclists, which potentially leads to beneficial adaptations in skeletal muscle without impairing muscle recovery 24 hours after exercise.