The Effects of Repeated-Sprint Training on Physical Fitness and Physiological Adaptation in Athletes: A Systematic Review and Meta-Analysis.

BACKGROUND: Repeated-sprint training (RST) is a common training method for enhancing physical fitness in athletes. To advance RST prescription, it is important to understand the effects of programming variables on physical fitness and physiological adaptation. OBJECTIVES: This study (1) quantifies the pooled effects of running RST on changes in 10 and 20 m sprint time, maximal oxygen consumption (VO2max), Yo-Yo Intermittent Recovery Test Level 1 (YYIR1) distance, repeated-sprint ability (RSA), countermovement jump (CMJ) height and change of direction (COD) ability in athletes, and (2) examines the moderating effects of program duration, training frequency, weekly volume, sprint modality, repetition distance, number of repetitions per set and number of sets per session on changes in these outcome measures. METHODS: Pubmed, SPORTDiscus and Scopus databases were searched for original research articles up to 04 July 2023, investigating RST in healthy, able-bodied athletes, between 14 and 35 years of age, and a performance calibre of trained or above. RST interventions were limited to repeated, maximal running (land-based) sprints of ≤ 10 s duration, with ≤ 60 s recovery, performed for 2-12 weeks. A Downs and Black checklist was used to assess the methodological quality of the included studies. Eligible data were analysed using multi-level mixed-effects meta-analysis, with standardised mean changes determined for all outcomes. Standardised effects [Hedges G (G)] were evaluated based on coverage of their confidence (compatibility) intervals (CI) using a strength and conditioning specific reference value of G = 0.25 to declare an improvement (i.e. G > 0.25) or impairment (i.e. G < - 0.25) in outcome measures. Applying the same analysis, the effects of programming variables were then evaluated against a reference RST program, consisting of three sets of 6 × 30 m straight-line sprints performed twice per week for 6 weeks (1200 m weekly volume). RESULTS: 40 publications were included in our investigation, with data from 48 RST groups (541 athletes) and 19 active control groups (213 athletes). Across all studies, the effects of RST were compatible with improvements in VO2max (G 0.56, 90% CI 0.32-0.80), YYIR1 distance (G 0.61, 90% CI 0.43-0.79), RSA decrement (G - 0.61, 90% CI - 0.85 to - 0.37), linear sprint times (10 m: G - 0.35, 90% CI - 0.48 to - 0.22; 20 m: G - 0.48, 90% CI - 0.69 to - 0.27), RSA average time (G - 0.34, 90% CI - 0.49 to - 0.18), CMJ height (G 0.26, 90% CI 0.13-0.39) and COD ability (G - 0.32, 90% CI - 0.52 to - 0.12). Compared with the reference RST program, the effects of manipulating training frequency (+ 1 session per week), program duration (+ 1 extra training week), RST volume (+ 200 m per week), number of reps (+ 2 per set), number of sets per session (+ 1 set) or rep distance (+ 10 m per rep) were either non-substantial or comparable with an impairment in at least one outcome measure per programming variable. CONCLUSIONS: Running-based RST improves speed, intermittent running performance, VO2max, RSA, COD ability and CMJ height in trained athletes. Performing three sets of 6 × 30 m sprints, twice per week for 6 weeks is effective for enhancing physical fitness and physiological adaptation. Additionally, since our findings do not provide conclusive support for the manipulation of RST variables, further work is needed to better understand how programming factors can be manipulated to augment training-induced adaptations. STUDY REGISTRATION: Open Science Framework registration https://doi.org/10.17605/OSF.IO/RVNDW .

The Acute Demands of Repeated-Sprint Training on Physiological, Neuromuscular, Perceptual and Performance Outcomes in Team Sport Athletes: A Systematic Review and Meta-analysis.

BACKGROUND: Repeated-sprint training (RST) involves maximal-effort, short-duration sprints (≤ 10 s) interspersed with brief recovery periods (≤ 60 s). Knowledge about the acute demands of RST and the influence of programming variables has implications for training prescription. OBJECTIVES: To investigate the physiological, neuromuscular, perceptual and performance demands of RST, while also examining the moderating effects of programming variables (sprint modality, number of repetitions per set, sprint repetition distance, inter-repetition rest modality and inter-repetition rest duration) on these outcomes. METHODS: The databases Pubmed, SPORTDiscus, MEDLINE and Scopus were searched for original research articles investigating overground running RST in team sport athletes ≥ 16 years. Eligible data were analysed using multi-level mixed effects meta-analysis, with meta-regression performed on outcomes with ~ 50 samples (10 per moderator) to examine the influence of programming factors. Effects were evaluated based on coverage of their confidence (compatibility) limits (CL) against elected thresholds of practical importance. RESULTS: From 908 data samples nested within 176 studies eligible for meta-analysis, the pooled effects (± 90% CL) of RST were as follows: average heart rate (HRavg) of 163 ± 9 bpm, peak heart rate (HRpeak) of 182 ± 3 bpm, average oxygen consumption of 42.4 ± 10.1 mL·kg-1·min-1, end-set blood lactate concentration (B[La]) of 10.7 ± 0.6 mmol·L-1, deciMax session ratings of perceived exertion (sRPE) of 6.5 ± 0.5 au, average sprint time (Savg) of 5.57 ± 0.26 s, best sprint time (Sbest) of 5.52 ± 0.27 s and percentage sprint decrement (Sdec) of 5.0 ± 0.3%. When compared with a reference protocol of 6 × 30 m straight-line sprints with 20 s passive inter-repetition rest, shuttle-based sprints were associated with a substantial increase in repetition time (Savg: 1.42 ± 0.11 s, Sbest: 1.55 ± 0.13 s), whereas the effect on sRPE was trivial (0.6 ± 0.9 au). Performing two more repetitions per set had a trivial effect on HRpeak (0.8 ± 1.0 bpm), B[La] (0.3 ± 0.2 mmol·L-1), sRPE (0.2 ± 0.2 au), Savg (0.01 ± 0.03) and Sdec (0.4; ± 0.2%). Sprinting 10 m further per repetition was associated with a substantial increase in B[La] (2.7; ± 0.7 mmol·L-1) and Sdec (1.7 ± 0.4%), whereas the effect on sRPE was trivial (0.7 ± 0.6). Resting for 10 s longer between repetitions was associated with a substantial reduction in B[La] (-1.1 ± 0.5 mmol·L-1), Savg (-0.09 ± 0.06 s) and Sdec (-1.4 ± 0.4%), while the effects on HRpeak (-0.7 ± 1.8 bpm) and sRPE (-0.5 ± 0.5 au) were trivial. All other moderating effects were compatible with both trivial and substantial effects [i.e. equal coverage of the confidence interval (CI) across a trivial and a substantial region in only one direction], or inconclusive (i.e. the CI spanned across substantial and trivial regions in both positive and negative directions). CONCLUSIONS: The physiological, neuromuscular, perceptual and performance demands of RST are substantial, with some of these outcomes moderated by the manipulation of programming variables. To amplify physiological demands and performance decrement, longer sprint distances (> 30 m) and shorter, inter-repetition rest (≤ 20 s) are recommended. Alternatively, to mitigate fatigue and enhance acute sprint performance, shorter sprint distances (e.g. 15-25 m) with longer, passive inter-repetition rest (≥ 30 s) are recommended.

The effect of caffeine on subsequent sleep: A systematic review and meta-analysis.

The consumption of caffeine in response to insufficient sleep may impair the onset and maintenance of subsequent sleep. This systematic review and meta-analysis investigated the effect of caffeine on the characteristics of night-time sleep, with the intent to identify the time after which caffeine should not be consumed prior to bedtime. A systematic search of the literature was undertaken with 24 studies included in the analysis. Caffeine consumption reduced total sleep time by 45 min and sleep efficiency by 7%, with an increase in sleep onset latency of 9 min and wake after sleep onset of 12 min. Duration (+6.1 min) and proportion (+1.7%) of light sleep (N1) increased with caffeine intake and the duration (-11.4 min) and proportion (-1.4%) of deep sleep (N3 and N4) decreased with caffeine intake. To avoid reductions in total sleep time, coffee (107 mg per 250 mL) should be consumed at least 8.8 h prior to bedtime and a standard serve of pre-workout supplement (217.5 mg) should be consumed at least 13.2 h prior to bedtime. The results of the present study provide evidence-based guidance for the appropriate consumption of caffeine to mitigate the deleterious effects on sleep.

Criterion Validity, and Interunit and Between-Day Reliability of the FLEX for Measuring Barbell Velocity During Commonly Used Resistance Training Exercises.

Weakley, J, Chalkley, D, Johnston, R, García-Ramos, A, Townshend, A, Dorrell, H, Pearson, M, Morrison, M, and Cole, M. Criterion validity, and interunit and between-day reliability of the FLEX for measuring barbell velocity during commonly used resistance training exercises. J Strength Cond Res 34(6): 1519-1524, 2020-The aim of this study was to assess the criterion validity, interunit reliability (accounting for technological and biological variance), and between-day reliability of a novel optic laser device (FLEX) for quantifying mean concentric velocity. To assess the validity against a three-dimensional motion capture system and interunit reliability with both technological and biological variation, 18 men and women completed repetitions at 20, 40, 60, 80, 90, and 100% of one repetition maximum in the free-weight barbell back squat and bench press. To assess interunit (technological only) reliability, a purpose-built, calibrated rig completed a set protocol with 2 devices. To assess between-day reliability of the technology, the same protocol was repeated 21 days later. Standardized bias, typical error of the estimate (TEE; %), and Pearson's correlation coefficient (r) were used to assess validity, whereas typical error and coefficient of variation (CV%) were calculated for reliability. Overall, TEE (±90 CL) between the FLEX and criterion measure was 0.03 (±0.004) and 0.04 (±0.005) m·s in the back squat and bench press, respectively. For measures of reliability, overall interunit technological variance (CV% [± 90% confidence interval]) was 3.96% (3.83-4.12) but increased to 9.82% (9.31-10.41) and 9.83% (9.17-10.61) in the back squat and bench press, respectively, when biological variance was introduced. Finally, the overall between-day reliability was 3.77% (3.63-3.91). These findings demonstrate that the FLEX provides valid and reliable mean concentric velocity outputs across a range of velocities. Thus, practitioners can confidently implement this device for the monitoring and prescription of resistance training loads.

Relationship Between 2 Standardized Tackling Proficiency Tests and Rugby League Match-Play Tackle Performance.

This study investigated the relationship between 2 different assessments of tackling ability, physical qualities, and match-play performance in semiprofessional rugby league players. A total of 18 semiprofessional rugby league players (mean [SD]: age = 23.1 [2.0] y and body mass = 98.8 [11.8] kg) underwent tests of upper- and lower-body strength and power. Tackling ability was assessed using video analysis of under- and over-the-ball tackle drills. A total of 2360 tackles were analyzed from match play. Over-the-ball tackle ability was positively related to the proportion of dominant tackles (Spearman rank-order correlation coefficients [rs] = .52; 95% confidence interval [CI] .07-.79, P = .03) and average play-the-ball speeds (rs = .50; 95% CI .04-.78, P = .03) and negatively related to tackles that conceded offloads (rs = -.55; 95% CI -.78 to .04, P = .04). Under-the-ball tackle ability was significantly related to the proportion of dominant tackles (rs = .57; 95% CI .14-.82, P = .01) and missed tackles (rs = -.48; 95% CI -.77 to .02, P = .05). Good over-the-ball tacklers performed proportionally more dominant tackles, allowed significantly fewer offloads, and had longer average play-the-ball speeds. Good under-the-ball tacklers missed proportionately fewer tackles. This study suggests that both the under-the-ball and over-the-ball standardized tackle assessments are associated with varying indicators of match-play tackle performance and justifies the practical utility of these tests to assess and develop both types of tackles.

The Use of Relative Speed Zones in Australian Football: Are We Really Measuring What We Think We Are?

OBJECTIVES: To examine the difference between absolute and relative workloads, injury likelihood, and the acute:chronic workload ratio (ACWR) in elite Australian football. DESIGN: Single-cohort, observational study. METHODS: Forty-five elite Australian football players from 1 club participated. Running workloads of players were tracked using Global Positioning System technology and were categorized using either (1) absolute, predefined speed thresholds or (2) relative, individualized speed thresholds. Players were divided into 3 equal groups based on maximum velocity: (1) faster, (2) moderate, or (3) slower. One- and 4-wk workloads were calculated, along with the ACWR. Injuries were recorded if they were noncontact in nature and resulted in "time loss." RESULTS: Faster players demonstrated a significant overestimation of very high-speed running (HSR) when compared with their relative thresholds (P = .01; effect size = -0.73). Similarly, slower players demonstrated an underestimation of high-(P = .06; effect size = 0.55) and very-high-speed (P = .01; effect size = 1.16) running when compared with their relative thresholds. For slower players, (1) greater amounts of relative very HSR had a greater risk of injury than less (relative risk [RR] = 8.30; P = .04) and (2) greater absolute high-speed chronic workloads demonstrated an increase in injury likelihood (RR = 2.28; P = .16), whereas greater relative high-speed chronic workloads offered a decrease in injury likelihood (RR = 0.33; P = .11). Faster players with a very-high-speed ACWR of >2.0 had a greater risk of injury than those between 0.49 and 0.99 for both absolute (RR = 10.31; P = .09) and relative (RR = 4.28; P = .13) workloads. CONCLUSIONS: The individualization of velocity thresholds significantly alters the amount of very HSR performed and should be considered in the prescription of training load.

An Alternative Test of Tackling Ability in Rugby League Players.

This study investigated the relationship between 2 tests of tackling ability, muscle strength, and power in semiprofessional rugby league players. Thirty-one players, 19 first-grade and 12 second-grade, underwent tests of muscle strength (1-repetition-maximum bench press, chin-up, and squat) and power (plyometric push-up and countermovement jump). Tackling ability was assessed via video analysis of under-and over-the-ball tackle drills. The first-grade players had significantly greater scores in both the under-the-ball (P = .03, effect size [ES] = 0.84, 95% CI 0.07-1.50) and over-the-ball tackling-ability tests (P < .001, ES =1.86, 95% CI 0.83-2.52) than the second-grade players. A large, significant relationship was found between under- and over-the-ball tackling ability (r = .55, 95% CI .24-.76, P = .001). Lower-body strength (r = .37, 95% CI .02-.64, P = .04) was moderately associated with under-the-ball tackling ability, whereas over-the-ball tackling ability was moderately associated with plyometric push-up performance (r = .39, 95% CI .04-.65, P = .03). This study found that over-the-ball tackling ability was significantly associated with under-the-ball tackling in semiprofessional rugby league players. Furthermore, it was found that, compared with the second-grade players, the first-grade players had superior tackle ability in both tackle drills. In this study it was observed that plyometric push-up peak power was significantly related to over-the-ball tackling ability and absolute lower-body strength was associated with under-the-ball tackling ability. These findings provide skill coaches and strength and conditioning staff a greater understanding of elements that contribute to effective tackling ability.

Relationship Between Preseason Training Load and In-Season Availability in Elite Australian Football Players.

OBJECTIVES: To investigate the relationship between the proportion of preseason training sessions completed and load and injury during the ensuing Australian Football League season. DESIGN: Single-cohort, observational study. METHODS: Forty-six elite male Australian football players from 1 club participated. Players were divided into 3 equal groups based on the amount of preseason training completed (high [HTL], >85% sessions completed; medium [MTL], 50-85% sessions completed; and low [LTL], <50% sessions completed). Global positioning system (GPS) technology was used to record training and game loads, with all injuries recorded and classified by club medical staff. Differences between groups were analyzed using a 2-way (group × training/competition phase) repeated-measures ANOVA, along with magnitude-based inferences. Injury incidence was expressed as injuries per 1000 h. RESULTS: The HTL and MTL groups completed a greater proportion of in-season training sessions (81.1% and 74.2%) and matches (76.7% and 76.1%) than the LTL (56.9% and 52.7%) group. Total distance and player load were significantly greater during the first half of the in-season period for the HTL (P = .03, ES = 0.88) and MTL (P = .02, ES = 0.93) groups than the LTL group. The relative risk of injury for the LTL group (26.8/1000 h) was 1.9 times greater than that for the HTL group (14.2/1000 h) (χ2 = 3.48, df = 2, P = .17). CONCLUSIONS: Completing a greater proportion of preseason training resulted in higher training loads and greater participation in training and competition during the competitive phase of the season.

The energetic cost of gait retraining: A pilot study of the acute effect.

OBJECTIVE: To investigate the acute effect of gait retraining aimed at reducing tibial peak positive acceleration (PPA) on energetic cost (VO2). DESIGN: Intervention with a pre/post-test design. SETTING: University biomechanics laboratory. PARTICIPANTS: 12 healthy male runners (23.4 ± 5.3 years, 179.7 ± 4.3 cm, 75.6 ± 9.2 kg). MAIN OUTCOME MEASURES: Tibial PPA and oxygen consumption (VO2) were measured after a five minute baseline run and at the end of a gait retraining session aimed at minimizing tibial PPA. RESULTS: Tibial PPA significantly decreased between baseline and after gait retraining (32.6%, p = 0.007). VO2 significantly increased between the two time periods (9.3%, p = 0.008). There was no correlation between change in tibial PPA and change in VO2 (p = 0.956, r = 0.018). CONCLUSION: Practitioners who aim to reduce injury risk by minimizing tibial PPA in runners need to consider the possible acute effect on performance as a result of changes in VO2. Further investigation is warranted to understand the energetic cost of different kinematic strategies used by individuals.

Calculating acute:chronic workload ratios using exponentially weighted moving averages provides a more sensitive indicator of injury likelihood than rolling averages.

OBJECTIVE: To determine if any differences exist between the rolling averages and exponentially weighted moving averages (EWMA) models of acute:chronic workload ratio (ACWR) calculation and subsequent injury risk. METHODS: A cohort of 59 elite Australian football players from 1 club participated in this 2-year study. Global positioning system (GPS) technology was used to quantify external workloads of players, and non-contact 'time-loss' injuries were recorded. The ACWR were calculated for a range of variables using 2 models: (1) rolling averages, and (2) EWMA. Logistic regression models were used to assess both the likelihood of sustaining an injury and the difference in injury likelihood between models. RESULTS: There were significant differences in the ACWR values between models for moderate (ACWR 1.0-1.49; p=0.021), high (ACWR 1.50-1.99; p=0.012) and very high (ACWR >2.0; p=0.001) ACWR ranges. Although both models demonstrated significant (p<0.05) associations between a very high ACWR (ie, >2.0) and an increase in injury risk for total distance ((relative risk, RR)=6.52-21.28) and high-speed distance (RR=5.87-13.43), the EWMA model was more sensitive for detecting this increased risk. The variance (R2) in injury explained by each ACWR model was significantly (p<0.05) greater using the EWMA model. CONCLUSIONS: These findings demonstrate that large spikes in workload are associated with an increased injury risk using both models, although the EWMA model is more sensitive to detect increases in injury risk with higher ACWR.

Physical qualities and activity profiles of sub-elite and recreational Australian football players.

OBJECTIVES: To investigate the relationship between physical qualities and match activity profiles of recreational Australian football players. DESIGN: Prospective cohort study. METHODS: Forty players from three recreational Australian football teams (Division One, Two and Three) underwent a battery of fitness tests (vertical jump, 10 and 40 m sprint, 6 m × 30 m repeated sprint test, Yo-Yo intermittent recovery level Two and 2-km time trial). The activity profiles of competitive match-play were quantified using 10-Hz Global Positioning System units. RESULTS: Division One players possessed greater maximum velocity, Yo-Yo level Two and 2-km time trial performances than Division Two and Three players. In addition, Division One players covered greater relative distance, and relative distances at moderate- and high-intensities during match-play than Division Two and Three players. Division Two players had better 2-km time trial performances than Division Three players. Positive associations (P < 0.05) were found between 10 m acceleration, maximum velocity, Yo-Yo level Two and 2-km time trial performances and relative distance, and relative distances covered at moderate- and high-intensities during match-play. Moderate relationships were found between vertical jump and relative distance and high-intensity running. CONCLUSIONS: Sub-elite Australian football players competing at a higher level exhibit greater physical qualities and match-play activity profiles than lesser-skilled recreational players. Acceleration and maximum velocity, 2-km time trial and Yo-Yo level Two performances discriminate between players of different playing levels, and are related to physical match performance in recreational Australian football. The development of these qualities is likely to contribute to improved match performance in recreational Australian football players.

Spontaneous pacing during overground hill running.

PURPOSE: To investigate speed regulation during overground running on undulating terrain. METHODS: After an initial laboratory session to calculate physiological thresholds, eight experienced runners completed a spontaneously paced time trial over three laps of an outdoor course involving uphill, downhill, and level sections. A portable gas analyzer, global positioning system receiver, and activity monitor were used to collect physiological, speed, and stride frequency data. RESULTS: Participants ran 23% slower on uphills and 13.8% faster on downhills compared with level sections. Speeds on level sections were significantly different for 78.4 +/- 7.0 s following an uphill and 23.6 +/- 2.2 s following a downhill. Speed changes were primarily regulated by stride length, which was 20.5% shorter uphill and 16.2% longer downhill, whereas stride frequency was relatively stable. Oxygen consumption averaged 100.4% of runner's individual ventilatory thresholds on uphills, 78.9% on downhills, and 89.3% on level sections. Approximately 89% of group-level speed was predicted using a modified gradient factor. Individuals adopted distinct pacing strategies, both across laps and as a function of gradient. CONCLUSIONS: Speed was best predicted using a weighted factor to account for prior and current gradients. Oxygen consumption (VO2) limited runner's speeds only on uphill sections and was maintained in line with individual ventilatory thresholds. Running speed showed larger individual variation on downhill sections, whereas speed on the level was systematically influenced by the preceding gradient. Runners who varied their pace more as a function of gradient showed a more consistent level of oxygen consumption. These results suggest that optimizing time on the level sections after hills offers the greatest potential to minimize overall time when running over undulating terrain.

Assessment of speed and position during human locomotion using nondifferential GPS.

PURPOSE: To validate a nondifferential global positioning system (GPS) to measure speed, displacement, and position during human locomotion. METHODS: Three healthy participants walked and ran over straight and curved courses for 59 and 34 trials, respectively. A nondifferential GPS receiver provided speed data by Doppler shift and change in GPS position over time, which were compared with actual speeds determined by chronometry. Displacement data from the GPS were compared with a surveyed 100-m section, and static positions were collected for 1 h and compared with the known geodetic point. RESULTS: GPS speed values on the straight course were closely correlated with actual speeds (Doppler shift: r = 0.9994, P < 0.001, Delta GPS position/time: r = 0.9984, P < 0.001). Actual speed errors were lowest using the Doppler shift method (90.8% of values within +/- 0.1 m x s(-1)). Speed was slightly underestimated on a curved path, though still highly correlated with actual speed (Doppler shift: r = 0.9985, P < 0.001, Delta GPS distance/time: r = 0.9973, P < 0.001). Distance measured by GPS was 100.46 +/- 0.49 m, and 86.5% of static points were within 1.5 m of the actual geodetic point (mean error: 1.08 +/- 0.34 m, range 0.69-2.10 m). CONCLUSIONS: Nondifferential GPS demonstrated a highly accurate estimation of speed across a wide range of human locomotion velocities using only the raw signal data with a minimal decrease in accuracy around bends. This high level of resolution was matched by accurate displacement and position data. Coupled with reduced size, cost, and ease of use, this method offers a valid alternative to differential GPS in the study of overground locomotion.