To Measure Peak Velocity in Soccer, Let the Players Sprint.

ABSTRACT: Kyprianou, E, Di Salvo, V, Lolli, L, Al Haddad, H, Villanueva, AM, Gregson, W, and Weston, M. To measure peak velocity in soccer, let the players sprint. J Strength Cond Res 36(1): 273-276, 2022-Expressing externals loads relative to a player's individual capacities has potential to enhance understanding of dose-response. Peak velocity is an important metric for the individualization process and is usually measured during a sprint test. Recently, however, peak velocity was reported to be faster during soccer matches when compared with a 40-m sprint test. With the aim of developing the practice of individualized training prescription and match evaluation, we examined whether the aforementioned finding replicates in a group of elite youth soccer players across a broader range of soccer activities. To do this, we compared the peak velocities of 12 full-time male youth soccer players (age 16.3 ± 0.8 years) recorded during a 40-m sprint test with peak velocity recorded during their routine activities (matches, sprints, and skill-based conditioning drills: small-sided games [SSG], medium-sided games [MSG], large-sided games [LSG]). All activities were monitored with 10-Hz global positioning systems (Catapult Optimeye S5, version 7.32) with the highest speed attained during each activity retained as the instantaneous peak velocity. Interpretation of clear between-activity differences in peak velocity was based on nonoverlap of the 95% confidence intervals for the mean difference between activities with sprint testing. Peak velocity was clearly faster for the sprint test (8.76 ± 0.39 m·s-1) when compared with matches (7.94 ± 0.49 m·s-1), LSG (6.94 ± 0.65 m·s-1), MSG (6.40 ± 0.75 m·s-1), and SSG (5.25 ± 0.92 m·s-1), but not sprints (8.50 ± 0.36 m·s-1). Our data show the necessity for 40-m sprint testing to determine peak velocity.

Variability of GPS-derived running performance during official matches in elite professional soccer players.

BACKGROUND: The aim of this study was to assess the match-to-match variability obtained using GPS devices, collected during official games in professional soccer players. METHODS: Global positioning system (GPS)-derived data from nineteen elite soccer players were collected over two consecutive seasons. Time-motion data for players with more than five full-match were analyzed (N.=202). Total distance covered (TD), TD>13-18 km/h, TD>18-21 km/h, TD>21 km/h, number of acceleration >2.5-4 m.s-2 and >4 m.s-2 were calculated. The match-to-match variation in running activity was assessed by the typical error expressed as a coefficient of variation (CV%) and the magnitude of the CV was calculated (effect size). RESULTS: When all players were pooled together, CVs ranged from 5% to 77% (first half) and from 5% to 90% (second half), for TD and number of acceleration >4 m.s-2, and the magnitude of the CVs were rated from small to moderate (effect size=0.57-0.98). The CVs were likely to increase with running/acceleration intensity, and were likely to differ between playing positions (e.g., TD>13-18 km/h 3.4% for second strikers vs. 14.2% for strikers and 14.9% for wide-defenders vs. 9.7% for wide-midfielders). CONCLUSIONS: Present findings indicate that variability in players' running performance is high in some variables and likely position-dependent. Such variability should be taken into account when using these variables to prescribe and/or monitor training intensity/load.

Monitoring changes in jump and sprint performance: best or average values?

This study compares different approaches to monitor changes in jump and sprint performance while using either the best or the average performance of repeated trials. One hundred two highly trained young footballers (U13 to U17) performed, in 2 different testing sessions separated by 4 mo, 3 countermovement jumps (n = 87) and 2 sprints (n = 98) over 40 m with 10-m splits to assess acceleration (first 10 m) and maximal sprinting speed (best split, MSS). Standardized group-average changes between the 2 testing periods and the typical error (TE) were calculated and compared for each method. The likelihood of substantial changes in performance for each individual player was also calculated. There was a small increase in jump performance (+6.1% for best and +7% for average performance). While 10-m time was likely unchanged (+~1.2% for both best and average performance), MSS showed likely small improvements (+~2.0% for both best and average performance). The TEs for jumping performance were 4.8% (90% confidence limits 4.3;5.6) and 4.3% (3.8;5.0) for best and average values, respectively; 1.8% (1.6;2.1) and 1.7% (1.5;1.9) for 10-m time and 2.0% (1.8;2.3) and 2.0% (1.8;2.3) for MSS. The standardized differences between TE were likely unclear or trivial for all comparisons (eg, 10-m, 0.01 [-0.09;0.10]). The numbers of players showing a likely increase or decrease in performance were 30/0 and 29/0 for best and average jump performances, 9/4 and 12/2 for 10-m times, and 33/4 and 33/4 for MSS. In conclusion, the 2 monitoring approaches are likely to provide similar outcomes.

Peak match speed and maximal sprinting speed in young soccer players: effect of age and playing position.

This study assessed the relationship between peak match speed (PMS) and maximal sprinting speed (MSS) in regard to age and playing positions. MSS and absolute PMS (PMSAbs) were collected from 180 male youth soccer players (U13-U17, 15.0 ± 1.2 y, 161.5 ± 9.2 cm, and 48.3 ± 8.7 kg). The fastest 10-m split over a 40-m sprint was used to determine MSS. PMSAbs was recorded using a global positioning system and was also expressed as a percentage of MSS (PMSRel). Sprint data were compared between age groups and between playing positions. Results showed that regardless of age and playing positions, faster players were likely to reach higher PMSAbs and possibly lower PMSRel. Despite a lower PMSAbs than in older groups (eg, 23.4 ± 1.8 vs 26.8 ± 1.9 km/h for U13 and U17, respectively, ES = 1.9 90%, confidence limits [1.6;2.1]), younger players reached a greater PMSRel (92.0% ± 6.3% vs. 87.2% ± 5.7% for U13 and U17, respectively, ES = -0.8 90% CL [-1.0;-0.5]). Playing position also affected PMSAbs and PMSRel, as strikers were likely to reach higher PMSAbs (eg, 27.0 ± 2.7 vs 23.6 ± 2.2 km/h for strikers and central midfielders, respectively, ES = 2.0 [1.7;2.2]) and PMSRel (eg, 93.6% ± 5.2% vs 85.3% ± 6.5% for strikers and central midfielders, respectively, ES = 1.0 [0.7;1.3]) than all other positions. The findings confirm that age and playing position affect the absolute and relative intensity of speed-related actions during matches.

Mechanical determinants of acceleration and maximal sprinting speed in highly trained young soccer players.

Abstract The aim of the present study was to examine, in highly trained young soccer players, the mechanical horizontal determinants of acceleration (Acc) and maximal sprinting speed (MSS). Eighty-six players (14.1 ± 2.4 year) performed a 40-m sprint to assess Acc and MSS. Speed was measured with a 100-Hz radar, and theoretical maximal velocity (V0), horizontal force (F0) and horizontal power (Pmax) were calculated. Within each age group, players were classified as high Acc/fast MSS (>2% faster than group mean), medium (between -2% and +2%), and low/slow (>2% slower). Acc and MSS were very largely correlated (-0.79; 90% confidence limit [-0.85; -0.71]). The determinants (multiple regression r2 = 0.84 [0.78; 0.89]) of Acc were V0 (partial r: 0.80 [0.72; 0.86]) and F0 (0.57 [0.44; 0.68]); those of MSS (r2 = 0.96 [0.94; 0.97]) were V0 (0.96 [0.94; 0.97]) and Pmax (0.73 [0.63; -0.80]). High/Med have likely greater F0 (Cohen's d: +0.8 [0.0; 1.5]), V0 (+0.6 [-0.1; 1.3]) and Pmax (+0.9 [0.2; 1.7]) than Low/Med. High/Fast have an almost certainly faster V0 (+2.1 [1.5; 2.7]) and a likely greater Pmax (+0.6 [-0.1; 1.3]) than High/Med, with no clear differences in F0 (-0.0 [-0.7; 0.6]). Speed may be a generic quality, but the mechanical horizontal determinants of Acc and MSS differ. While maximal speed training may improve both Acc and MSS, improving horizontal force production capability may be efficient to enhance sprinting performance over short distances.

Relationships between anthropometric measures and athletic performance, with special reference to repeated-sprint ability, in the Qatar national soccer team.

The aim of this study was to determine potential relationships between anthropometric parameters and athletic performance with special consideration to repeated-sprint ability (RSA). Sixteen players of the senior male Qatar national soccer team performed a series of anthropometric and physical tests including countermovement jumps without (CMJ) and with free arms (CMJwA), straight-line 20 m sprint, RSA (6 × 35 m with 10 s recovery) and incremental field test. Significant (P < 0.05) relationships occurred between muscle-to-bone ratio and both CMJs height (r ranging from 0.56 to 0.69) as well as with all RSA-related variables (r < -0.53 for sprinting times and r = 0.54 for maximal sprinting speed) with the exception of the sprint decrement score (Sdec). The sum of six skinfolds and adipose mass index were largely correlated with Sdec (r = 0.68, P < 0.01 and r = 0.55, P < 0.05, respectively) but not with total time (TT, r = 0.44 and 0.33, P > 0.05, respectively) or any standard athletic tests. Multiple regression analyses indicated that muscular cross-sectional area for mid-thigh, adipose index, straight-line 20 m time, maximal sprinting speed and CMJwA are the strongest predictors of Sdec (r(2) = 0.89) and TT (r(2) = 0.95) during our RSA test. In the Qatar national soccer team, players' power-related qualities and RSA are associated with a high muscular profile and a low adiposity. This supports the relevance of explosive power for the soccer players and the larger importance of neuromuscular qualities determining the RSA.

Monitoring accelerations with GPS in football: time to slow down?

The aims of the current study were to examine the magnitude of between-GPS-models differences in commonly reported running-based measures in football, examine between-units variability, and assess the effect of software updates on these measures. Fifty identical-brand GPS units (15 SPI-proX and 35 SPIproX2, 15 Hz, GPSports, Canberra, Australia) were attached to a custom-made plastic sled towed by a player performing simulated match running activities. GPS data collected during training sessions over 4 wk from 4 professional football players (N = 53 files) were also analyzed before and after 2 manufacturer-supplied software updates. There were substantial differences between the different models (eg, standardized difference for the number of acceleration >4 m/s2 = 2.1; 90% confidence limits [1.4, 2.7], with 100% chance of a true difference). Between-units variations ranged from 1% (maximal speed) to 56% (number of deceleration >4 m/s2). Some GPS units measured 2-6 times more acceleration/deceleration occurrences than others. Software updates did not substantially affect the distance covered at different speeds or peak speed reached, but 1 of the updates led to large and small decreases in the occurrence of accelerations (-1.24; -1.32, -1.15) and decelerations (-0.45; -0.48, -0.41), respectively. Practitioners are advised to apply care when comparing data collected with different models or units or when updating their software. The metrics of accelerations and decelerations show the most variability in GPS monitoring and must be interpreted cautiously.

Effect of acute hypoxia on post-exercise parasympathetic reactivation in healthy men.

In this study we assessed the effect of acute hypoxia on post-exercise parasympathetic reactivation inferred from heart rate (HR) recovery (HRR) and HR variability (HRV) indices. Ten healthy males participated in this study. Following 10 min of seated rest, participants performed 5 min of submaximal running at the speed associated with the first ventilatory threshold (Sub) followed by a 20-s all-out supramaximal sprint (Supra). Both Sub and Supra runs were immediately followed by 15 min of seated passive recovery. The resting and exercise sequence were performed in both normoxia (N) and normobaric hypoxia (H; FiO(2) = 15.4%). HRR indices (e.g., heart beats recovered in the first minute after exercise cessation, HRR(60s)) and vagal-related HRV indices [i.e., natural logarithm of the square root of the mean of the sum of the squared differences between adjacent normal R-R intervals (Ln rMSSD)] were calculated for both conditions. Difference in the changes between N and H for all HR-derived indices were also calculated for both Sub and Supra. HRR(60s) was greater in N compared with H following Sub only (60 ± 14 vs. 52 ± 19 beats min(-1), P = 0.016). Ln rMSSD was greater in N compared with H (post Sub: 3.60 ± 0.45 vs. 3.28 ± 0.44 ms in N and H, respectively, and post Supra: 2.66 ± 0.54 vs. 2.65 ± 0.63 ms, main condition effect P = 0.02). When comparing the difference in the changes, hypoxia decreased HRR(60s) (-14.3% ± 17.2 vs. 5.2% ± 19.3; following Sub and Supra, respectively; P = 0.03) and Ln rMSSD (-8.6% ± 7.0 vs. 2.0% ± 13.3, following Sub and Supra, respectively; P = 0.08, Cohen's effect size = 0.62) more following Sub than Supra. While hypoxia may delay parasympathetic reactivation following submaximal exercise, its effect is not apparent following supramaximal exercise. This may suggest that the effect of blood O(2) partial pressure on parasympathetic reactivation is limited under heightened sympathetic activation.

Effect of daily cold water immersion on heart rate variability and subjective ratings of well-being in highly trained swimmers.

PURPOSE: We investigated the effect of daily cold water immersion (CWI), during a typical training week, on parasympathetic activity and subjective ratings of well-being. METHODS: Over two different weeks, eight highly trained swimmers (4 men; 19.6 ± 3.2 y) performed their usual training load (5 d/wk, approx. 21 h/wk). Last training session of each training day was immediately followed by 5 min of seated recovery, in randomized order, with CWI (15°C) or without (CON). Each morning before the first training session (6:30 AM) during the two experimental weeks, subjective ratings of well-being (eg, quality of sleep) were assessed and the R-R intervals were recorded for 5 min in supine position. A vagal-related index (ie, natural logarithm of the square root of the mean of the sum of the squares of differences between adjacent normal R-R intervals; Ln rMSSD) was calculated from the last 3-min segment. RESULTS: Compared with CON, CWI effect on Ln rMSSD was rated as possibly beneficial on day 2 [7.0% (-3; 19)], likely beneficial on day 3 [20.0% (1.5; 43.5)], very likely beneficial on day 4 [30.4% (12.2; 51.6)] and likely beneficial on day 5 [24.1% (-0.4; 54.8)]. Cold water immersion was associated with a likely greater quality of sleep on day 2 [30.0% (2.7; 64.6)], very likely on day 3 [31.0% (5.0; 63.1)] and likely on day 4 [38.6% (11.4; 72.4)] when compared with CON. CONCLUSION: Five minutes of CWI following training can reduce the usual exercise-induced decrease in parasympathetic activity and is associated with improved rating of perceived sleep quality.

Effect of maturation on hemodynamic and autonomic control recovery following maximal running exercise in highly trained young soccer players.

The purpose of this study was to examine the effect of maturation on post-exercise hemodynamic and autonomic responses. Fifty-five highly trained young male soccer players (12-18 years) classified as pre-, circum-, or post-peak height velocity (PHV) performed a graded running test to exhaustion on a treadmill. Before (Pre) and after (5th-10th min, Post) exercise, heart rate (HR), stroke volume (SV), cardiac output (CO), arterial pressure (AP), and total peripheral resistance (TPR) were monitored. Parasympathetic (high frequency [HF(RR)] of HR variability (HRV) and baroreflex sensitivity [Ln BRS]) and sympathetic activity (low frequency [LF(SAP)] of systolic AP variability) were estimated. Post-exercise blood lactate [La](b), the HR recovery (HRR) time constant, and parasympathetic reactivation (time-varying HRV analysis) were assessed. In all three groups, exercise resulted in increased HR, CO, AP, and LF(SAP) (P < 0.001), decreased SV, HF(RR), and Ln BRS (all P < 0.001), and no change in TPR (P = 0.98). There was no "maturation × time" interaction for any of the hemodynamic or autonomic variables (all P > 0.22). After exercise, pre-PHV players displayed lower SV, CO, and [La](b), faster HRR and greater parasympathetic reactivation compared with circum- and post-PHV players. Multiple regression analysis showed that lean muscle mass, [La](b), and Pre parasympathetic activity were the strongest predictors of HRR (r(2) = 0.62, P < 0.001). While pre-PHV players displayed a faster HRR and greater post-exercise parasympathetic reactivation, maturation had little influence on the hemodynamic and autonomic responses following maximal running exercise. HRR relates to lean muscle mass, blood acidosis, and intrinsic parasympathetic function, with less evident impact of post-exercise autonomic function.

Effect of cold or thermoneutral water immersion on post-exercise heart rate recovery and heart rate variability indices.

This study aimed to investigate the effect of cold and thermoneutral water immersion on post-exercise parasympathetic reactivation, inferred from heart rate (HR) recovery (HRR) and HR variability (HRV) indices. Twelve men performed, on three separate occasions, an intermittent exercise bout (all-out 30-s Wingate test, 5 min seated recovery, followed by 5 min of submaximal running exercise), randomly followed by 5 min of passive (seated) recovery under either cold (CWI), thermoneutral water immersion (TWI) or control (CON) conditions. HRR indices (e.g., heart beats recovered in the first minute after exercise cessation, HRR(60)(s)) and vagal-related HRV indices (i.e., natural logarithm of the square root of the mean of the sum of the squares of differences between adjacent normal R-R intervals (Ln rMSSD)) were calculated for the three recovery conditions. HRR(60)(s) was faster in water immersion compared with CON conditions [30+/-9 beats min(-)(1) for CON vs. 43+/- 10 beats min(-)(1) for TWI (P=0.003) and 40+/-13 beats min(-)(1) for CWI (P=0.017)], while no difference was found between CWI and TWI (P=0.763). Ln rMSSD was higher in CWI (2.32+/-0.67 ms) compared with CON (1.98+/-0.74 ms, P=0.05) and TWI (2.01+/-0.61 ms, P=0.08; aES=1.07) conditions, with no difference between CON and TWI (P=0.964). Water immersion is a simple and efficient means of immediately triggering post-exercise parasympathetic activity, with colder immersion temperatures likely to be more effective at increasing parasympathetic activity.

Effect of cold water immersion on 100-m sprint performance in well-trained swimmers.

The aim of the present study was to examine the effect of cold water immersion (CWI) on sprint swimming performance in simulated competition conditions. Ten well-trained swimmers (5 males, 5 females; 19.0 +/- 3.9 years) performed two 100-m swimming sprints (S1 and S2) interspersed with a 30-min passive recovery period, during which athletes were randomly assigned to 5 min of CWI (14 degrees C) or an out-of-water control condition (CON 28 degrees C). During tests, sprint times, heart rate (HR), pre- and post-race parasympathetic activity via HR variability (natural logarithm of the square root of the mean of the sum of the squares of differences between adjacent normal R-R intervals; Ln rMSSD) and blood lactate accumulation ([La](ac)) and clearance ([La](cle)) were recorded. Rates of perceived recovery (RPR) and exertion (RPE) were evaluated before and after each sprint. CWI was associated with a 'likely' decrease in swimming performance [1.8% (90% CI 0.2, 3.5)], as well as 'likely' lower peak HR [-1.9% (-3.6, -0.2)]. CWI was also associated with a 'likely' smaller decrease in Ln rMSSD after the first sprint [-16.7% (-30.9, -4.1)]. RPR was 'likely' better [+27.2% (-3.7, 68.0)] following CWI. 'unclear' effects were observed for [La](ac) [+24.7% (-13.4, 79.5)], [La](cle) [-7.6% (-24.2, 12.7)] or RPE [+2.0% (-12.3, 18.5)]. Following CWI, changes in sprint times were 'largely' correlated with changes in peak HR (r = 0.80). Despite a subjective perception of improved recovery following CWI, this recovery intervention resulted in slower swimming times in well-trained athletes swimming in simulated competition conditions.

Effect of in- versus out-of-water recovery on repeated swimming sprint performance.

The aim of this study was to compare the effect of passive in- (IN) versus out-of-(OUT) water recovery on performance during repeated maximal sprint swimming. Nine well-trained male swimmers (21 +/- 3.5 years) performed six repeated maximal 50-m sprints (RS), departing every 2 min, interspersed with either IN or OUT recovery. Best (RS(b)) and mean (RS(m)) RS times, percentage speed decrement (%Dec) and between-sprint heart rate recovery (HRR(80s)) were calculated for both conditions. Blood lactate was measured after the third ([La](b) S3) and sixth sprints (post [La](b)). Rating of perceived recovery level (REC) and exertion (RPE) were collected before and after each sprint. Repeated sprint performance was significantly lower in the OUT condition (i.e., for RS(m), P = 0.02, +1.3%, 90% CI -0.7, 3.2%). OUT was also associated with poorer HRR(80s) (P < 0.001, -23%, 90% CI -34, -10%) and higher [La](b) S3 (P < 0.01, +13%, 90% CI -1, 29%). Post [La](b), however, was similar (P = 0.44, +1%, 90% CI -7, 10%). RPE and REC were not significantly different between the two conditions (all P > 0.43). To conclude, present results confirm the beneficial effect of the IN condition on repeated swim sprint performance, but also suggest that the OUT recovery modality could be an effective training practice for eliciting a low intramuscular energy status.

Influence of cold water face immersion on post-exercise parasympathetic reactivation.

The aim of the present study was to investigate the effect of cold water face immersion on post-exercise parasympathetic reactivation, inferred from heart rate (HR) recovery (HRR) and HR variability (HRV) indices. Thirteen men performed, on two different occasions, an intermittent exercise (i.e., an all-out 30-s Wingate test followed by a 5-min run at 45% of the speed reached at the end of the 30-15 Intermittent Fitness test, interspersed with 5 min of seated recovery), randomly followed by 5 min of passive (seated) recovery with either cold water face immersion (CWFI) or control (CON). HR was recorded beat-to-beat and vagal-related HRV indices (i.e., natural logarithm of the high-frequency band, LnHF, and natural logarithm of the square root of the mean sum of squared differences between adjacent normal R-R intervals, Ln rMSSD) and HRR (e.g., heart beats recovered in the first minute after exercise cessation) were calculated for both recovery conditions. Parasympathetic reactivation was faster for the CWFI condition, as indicated by higher LnHF (P = 0.004), Ln rMSSD (P = 0.026) and HRR (P = 0.002) values for the CWFI compared with the CON condition. Cold water face immersion appears to be a simple and efficient means of immediately accelerating post-exercise parasympathetic reactivation.

Nocturnal heart rate variability following supramaximal intermittent exercise.

PURPOSE: To assess the effect of supramaximal intermittent exercise on long-term cardiac autonomic activity, inferred from heart rate variability (HRV). METHODS: Eleven healthy males performed a series of two consecutive intermittent 15-s runs at 95% VIFT (i.e., speed reached at the end of the 30-15 Intermittent Fitness Test) interspersed with 15 s of active recovery at 45% VIFT until exhaustion. Beat-to-beat intervals were recorded during two consecutive nights (habituation night and 1st night) before, 10 min before and immediately after exercise, as well as 12 h (2nd night) and 36 h (3rd night) after supramaximal intermittent exercise. The HRV indices were calculated from the last 5 min of resting and recovery periods, and the first 10 min of the first estimated slow wave sleep period. RESULTS: Immediate post-supramaximal exercise vagal-related HRV indices were significantly lower than immediate pre-supramaximal exercise values (P < .001). Most vagal-related indices were lower during the 2nd night compared with the 1st night (eg, mean RR intervals, P = .03). Compared with the 2nd night, vagal-related HRV indices were significantly higher during the 3rd night. Variables were not different between the 1st and 3rd nights; however, we noted a tendency (adjusted effect size, aES) for an increased normalized high-frequency component (P = .06 and aES = 0.70) and a tendency toward a decreased low-frequency component (P = .06 and aES = 0.74). CONCLUSION: Results confirm the strong influence of exercise intensity on short- and long-term postexercise heart rate variability recovery and might help explain the high efficiency of supramaximal training for enhancing indices of cardiorespiratory fitness.

Cardiorespiratory and cardiac autonomic responses to 30-15 intermittent fitness test in team sport players.

The 30-15 Intermittent Fitness Test (30-15IFT) is an attractive alternative to classic continuous incremental field tests for defining a reference velocity for interval training prescription in team sport athletes. The aim of the present study was to compare cardiorespiratory and autonomic responses to 30-15IFT with those observed during a standard continuous test (CT). In 20 team sport players (20.9 +/- 2.2 years), cardiopulmonary parameters were measured during exercise and for 10 minutes after both tests. Final running velocity, peak lactate ([La]peak), and rating of perceived exertion (RPE) were also measured. Parasympathetic function was assessed during the postexercise recovery phase via heart rate (HR) recovery time constant (HRR[tau]) and HR variability (HRV) vagal-related indices. At exhaustion, no difference was observed in peak oxygen uptake VO2peak), respiratory exchange ratio, HR, or RPE between 30-15IFT and CT. In contrast, 30-15IFT led to significantly higher minute ventilation, [La]peak, and final velocity than CT (p < 0.05 for all parameters). All maximal cardiorespiratory variables observed during both tests were moderately to well correlated (e.g., r = 0.76, p = 0.001 for [latin capital VO2peak). Regarding ventilatory thresholds (VThs), all cardiorespiratory measurements were similar and well correlated between the 2 tests. Parasympathetic function was lower after 30-15IFT than after CT, as indicated by significantly longer HHR[tau] (81.9 +/- 18.2 vs. 60.5 +/- 19.5 for 30-15IFT and CT, respectively, p < 0.001) and lower HRV vagal-related indices (i.e., the root mean square of successive R-R intervals differences [rMSSD]: 4.1 +/- 2.4 and 7.0 +/- 4.9 milliseconds, p < 0.05). In conclusion, the 30-15IFT is accurate for assessing VThs and VO2peak, but it alters postexercise parasympathetic function more than a continuous incremental protocol.