Predicting running velocity at blood lactate threshold from running performance tests in adolescent boys

The purpose of this study was to investigate the relationship between running velocity at blood lactate threshold (VLT) and running performance (50 m, 40 s and 5 min) in boys aged 14 years at puberty (n = 30) and young men aged 16-20 years (n = 39), and to examine the possibility of predicting VLT from running performances in boys during adolescence. Special attention was also paid as to whether these parameters are related to bone maturity in boys at puberty. After allowing for chronological age, height, weight and fat content, all the running performances were positively correlated to bone maturity in non-active boys at puberty. In contrast, VLT was negatively correlated to bone maturity. In spite of these results, VLT was significantly related to performance in the 5 min run in both the boys and the young men. However, the correlation coefficient for the former was significantly lower than that for the latter. The 5 min and 40 s runs were selected by stepwise regression analysis for predicting VLT in the two groups. The same predictor was selected from the combined data from both groups using the following equation: VLT(m X min-1) = 124 - 0.83 X 40 s run(m) + 0.202 X 5 min run(m). The correlation between actual and estimated VLT, and the standard error of the estimate of this formula were 0.726 and - 5 + 15 m X min-1 in the boys, and 0.880 and 4 + 11 m X min-1 in the young men, respectively. This formula was similar in precision to the formulae obtained from the data in each individual group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Physiological responses during prolonged exercise at the power output corresponding to the blood lactate threshold

Heart rate (HR) and oxygen uptake (VO2) at the mechanical power (W) corresponding to the capillary blood lactate ([la]cap) of 4 mmol.l-1 (Wlt) were measured in 34 healthy male subjects during incremental exercise (Winc). On the basis of these measurements, the subjects were asked to cycle at Wlt for 60 min (steady-state exercise, Wss). Twenty subjects could not reach the target time (mean exhaustion time, te, 38.2 min, SD 5.3), while 6 of the 14 remaining subjects declared themselves exhausted at the end of exercise. The final [la]cap if the two groups of exhausted subjects were 5.3 mmol.l-1, SD 2.3 and 4.3 mmol.l-1, SD 1.1, respectively. At the end of Wss, [la]cap and HR were significantly lower in the 8 unexhausted subjects than in the other subjects. This group also had a lower HR at Wlt during Winc. The HR and VO2 appeared to be higher during Wss than during Winc. When all subjects were ranked according to their te during Wss, Wlt (expressed per kilogram of body mass) was found to be negatively related to te. In conclusion, during Winc, measurements of physiological variables at fixed [la]cap give a poor prediction of their trends during Wss and of the relative te; at the same work load [la]cap can be quite different in the two experimental conditions. Furthermore, resistance to exercise fatigue at Wlt seems lower in the fitter subjects.     

Relationship between lactate threshold during running and relative gastrocnemius area

This study examined the relationship between the work rate at which blood lactate accumulation begins (lactate threshold) during running and relative gastrocnemius area in four different groups. Twenty nonathletic and 11 athletic boys (age 9-12 yr), 15 female adult runners, and 11 male nonathletic students participated in this study. The muscle composition of the leg and thigh were measured by ultrasound. The lactate threshold was assessed in terms of both the absolute work rate (ml.kg-1.min-1) and relative work rate. The relative cross-sectional area of the gastrocnemius to the plantar flexor (relative gastrocnemius area) was significantly negatively related to the absolute and relative lactate threshold in all groups. These results suggest that the relative gastrocnemius area may play an important role in determining the relative and absolute lactate threshold during running.     

Effects of delayed onset muscle soreness on selected physiological responses to submaximal running

This study examined the effects of delayed-onset muscle soreness (DOMS) on selected physiological responses to submaximal exercise. Seven male and four female subjects (Ss) aged 21-37 years completed two submaximal running sessions at an individualized pace corresponding to a blood lactate concentration (bLa) of approximately 2.5 mmol x L(-1). Following the first session (T1), Ss performed a series of lower extremity resistance exercises designed to induce DOMS. Subjects were then retested (T2) 24-30 hours later, during which time all Ss experienced DOMS. Oxygen uptake, heart rate (HR), respiratory exchange ratio, rating of perceived exertion (RPE), and bLa were measured every 6 minutes. Significant trial effects (p < 0.05) were observed for HR and RPE. HR was significantly higher during T1 at minutes 6 and 12 (p < 0.05), and RPE values were significantly higher at T2 during all recording periods (p < 0.05). Results from this study suggest that DOMS does not affect submaximal oxygen uptake. However, DOMS does appear to affect one's perception of effort.     

Effects of training at and above the lactate threshold on the lactate threshold and maximal oxygen uptake

Thirty-three college women (mean age = 21.8 years) participated in a 5 d X wk-1, 12 week training program. Subjects were randomly assigned to 3 groups, above lactate threshold (greater than LT) (N = 11; trained at 69 watts above the workload associated with LT), = LT (N = 12; trained at the work load associated with LT) and control (C) (N = 10). Subjects were assessed for VO2max, VO2LT, VO2LT/VO2max, before and after training, using a discontinuous 3 min incremental (starting at 0 watts increasing 34 watts each work load) protocol on a cycle ergometer (Monark). Respiratory gas exchange measures were determined using standard open circuit spirometry while LT was determined from blood samples taken immediately following each work load from an indwelling venous catheter located in the back of a heated hand. Body composition parameters were determined before and after training via hydrostatic weighing. Training work loads were equated so that each subject expended approximately 1465 kJ per training session (Monark cycle ergometer) regardless of training intensity. Pretraining, no significant differences existed between groups for any variable. Post training the greater than LT group had significantly higher VO2max (13%), VO2LT (47%) and VO2LT/VO2max (33%) values as compared to C (p less than .05). Within group comparisons revealed that none of the groups significantly changed VO2max as a result of training, only the greater than LT group showed a significant increase in VO2LT (48%) (p less than .05), while both the = LT and greater than LT group showed significant increases in VO2LT/VO2max (= LT 16%, greater than LT 42% (p less than .05)).(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of a field-based test to estimate functional threshold power and power output at lactate threshold

It has been proposed that field-based tests (FT) used to estimate functional threshold power (FTP) result in power output (PO) equivalent to PO at lactate threshold (LT). However, anecdotal evidence from regional cycling teams tested for LT in our laboratory suggested that PO at LT underestimated FTP. It was hypothesized that estimated FTP is not equivalent to PO at LT. The LT and estimated FTP were measured in 7 trained male competitive cyclists (VO2max = 65.3 ± 1.6 ml O2·kg(-1)·min(-1)). The FTP was estimated from an 8-minute FT and compared with PO at LT using 2 methods; LT(Δ1), a 1 mmol·L(-1) or greater rise in blood lactate in response to an increase in workload and LT(4.0), blood lactate of 4.0 mmol·L(-1). The estimated FTP was equivalent to PO at LT(4.0) and greater than PO at LT(Δ1). VO2max explained 93% of the variance in individual PO during the 8-minute FT. When the 8-minute FT PO was expressed relative to maximal PO from the VO2max test (individual exercise performance), VO2max explained 64% of the variance in individual exercise performance. The PO at LT was not related to 8-minute FT PO. In conclusion, FTP estimated from an 8-minute FT is equivalent to PO at LT if LT(4.0) is used but is not equivalent for all methods of LT determination including LT(Δ1).     

Reverse lactate threshold test accurately predicts maximal lactate steady state and 5 km performance in running

This study evaluated the accuracy of the reverse lactate threshold (RLT) and the onset of blood lactate accumulation (OBLA; 4 mmol·L^-1) to determine the running speed at the maximal lactate steady state (MLSS) and 5 km running performance in a field test approach. Study 1: 16 participants performed an RLT test, and 2 or more constant-speed tests, lasting 30 minutes each, to determine running speed at the MLSS. Study 2: 23 participants performed an RLT test and a 5000 m all-out run as an indicator of performance. The RLT test consisted of an initial lactate-priming segment, in which running speed was increased stepwise up to ~5% above the estimated MLSS, followed by a reverse segment in which speed was decreased by 0.1 m·s^-1 every 180 s. RLT was determined using the highest lactate equivalent ([La^-]/running speed) during the reverse segment. OBLA was determined during the priming segment and was set at a value of 4 mmol∙L¹. The mean difference in MLSS was +0.06 ± 0.05 m·s^-1 for RLT, and +0.13 ± 0.23 m·s^-1 for OBLA. OBLA showed a good concordance with the MLSS (ICC = 0.83), whereas RLT revealed excellent concordance with the MLSS with an ICC = 0.98. RLT showed a very high correlation with 5000 m speed (r = 0.97). The RLT exhibited exceptional agreement to MLSS and 5000 m running performance. Due to this high accuracy, especially concerning the small intraindividual differences, the RLT test may be superior to common threshold concepts. Further research is needed to evaluate its sensitivity during the training process.     

Validity of the heart rate deflection point as a predictor of lactate threshold during running.

During an incremental run test, some researchers consistently observe a heart rate (HR) deflection at higher speeds, but others do not. The present study was designed to investigate whether differences in test protocols could explain the discrepancy. Additionally, we sought to determine whether the HR deflection point accurately predicts lactate threshold (LT). Eight trained runners performed four tests each: 1) a treadmill test for maximal O(2) uptake, 2) a Conconi test on a 400-m track with speeds increasing approximately 0.5 km/h every 200 m, 3) a continuous treadmill run with speeds increasing 0.5 km/h every minute, and 4) a continuous LT treadmill test in which 3-min stages were used. All subjects demonstrated an HR deflection on the track, but only one-half of the subjects showed an HR deflection on the treadmill. On the track the shortening of stages with increasing speeds contributed to a loss of linearity in the speed-HR relationship. Additionally, the HR deflection point overestimated the LT when a continuous treadmill LT protocol was used. In conclusion, the HR deflection point was not an accurate predictor of LT in the present study.     

Blood glucose responses in humans mirror lactate responses for individual anaerobic threshold and for lactate minimum in track tests

The equilibrium point between blood lactate production and removal (La-(min)) and the individual anaerobic threshold (IAT) protocols have been used to evaluate exercise. During progressive exercise, blood lactate [La-]b, catecholamine and cortisol concentrations, show exponential increases at upper anaerobic threshold intensities. Since these hormones enhance blood glucose concentrations [Glc]b, this study investigated the [Glc] and [La-]b responses during incremental tests and the possibility of considering the individual glucose threshold (IGT) and glucose minimum (Glc(min)) in addition to IAT and La-(min) in evaluating exercise. A group of 15 male endurance runners ran in four tests on the track 3000 m run (v3km); IAT and IGT - 8 x 800 m runs at velocities between 84% and 102% of v3km; La-(min) and Glc(min) - after lactic acidosis induced by a 500-m sprint, the subjects ran 6 x 800 m at intensities between 87% and 97% of v3km; endurance test (ET) - 30 min at the velocity of IAT. Capillary blood (25 microl) was collected for [La-]b and [Glc]b measurements. The IAT and IGT were determined by [La-]b and [Glc]b kinetics during the second test. The La-(min) and Glc(min) were determined considering the lowest [La-] and [Glc]b during the third test. No differences were observed (P < 0.05) and high correlations were obtained between the velocities at IAT [283 (SD 19) and IGT 281 (SD 21) m. x min(-1); r = 0.096; P < 0.001] and between La-(min) [285 (SD 21)] and Glc(min) [287 (SD 20) m. x min(-1) r = 0.77; P < 0.05]. During ET, the [La-]b reached 5.0 (SD 1.1) and 5.3 (SD 1.0) mmol x l(-1) at 20 and 30 min, respectively (P > 0.05). We concluded that for these subjects it was possible to evaluate the aerobic capacity by IGT and Glc(min) as well as by IAT and La-(min).     

Cardiorespiratory and neuromuscular responses to motocross riding

The aim of the present study was to examine physiological and neuromuscular responses during motocross riding at individual maximal speed together with the riding-induced changes in maximal isometric force production. Seven A-level (group A) and 5 hobby-class (group H) motocross-riders performed a 30-minute riding test on a motocross track and maximal muscle strength and oxygen uptake (VO2max) tests in a laboratory. During the riding the mean (+/-SD) VO2 reduced in group A from 86 +/- 10% to 69 +/- 6% of the maximum (P < 0.001), whereas in group H the corresponding reduction was from 94 +/- 25% to 82 +/- 20% (P < 0.05). This relative VO2 during the riding correlated with riding speed (r = 0.70, P < 0.01). Heart rate (HR) was maintained at the level of 97 +/- 7% of its maximum in group A and at 98 +/- 3% in group H. Mean muscle activation of the lower body during riding varied between 24% and 38% of its maximum in group A and between 40% and 45% in group H. In conclusion, motocross is a sport that causes great physical stress and demands on both skill and physical capacity of the rider. Physical stress occurs as the result of handling of the bike when receiving continuous impacts in the situation requiring both aerobic and anaerobic metabolism. Our data suggest that both maximal capacity and strain during the ride should be measured to analyze the true physiological and neuromuscular demands of motocross ride. For the practice, this study strongly suggests to train not only aerobic and anaerobic capacity but also to use strength and power training for successful motocross riding.     

Heart rate at lactate threshold and cycling time trials

The purpose of this investigation was to relate the heart rate and lactate response during simulated cycling time trials to incremental laboratory tests. Subjects (N = 10) were tested for .V(O2)max (56.1 +/- 2.4 ml.kg(-1).min(-1) ) and lactate threshold during incremental tests to exhaustion. Power output and heart rate (HR) at threshold was assessed by 3 methods: lactate deflection point (LaT), onset of blood lactate accumulation (OBLA), and the point on the lactate curve at maximal distance from a line connecting starting and finishing power output (Dmax). Power output determined at these thresholds was 282.1 +/-4.2, 302.5 +/-1.3, and 296.0 +/- 1.8 W, respectively, whereas HR was determined to be 88.6 +/- 0.01, 92.2 +/- 0.01, and 91.0 +/- 0.01% of maximum, respectively. Power output and HR were significantly lower for LaT than for the other 2 methods (p < 0.05). On separate visits, cyclists were instructed to perform maximum efforts for 30 and 60 minutes (30TT and 60TT). Lactate, HR, perceived exertion (RPE), and metabolic variables were measured during the time trials. During the 30TT, participants sustained a significantly higher lactate level (5.29 +/- 0.3 vs. 3.43 +/- 0.3 mmol.L(-1), p < 0.001), percentage of maximum HR (%HRmax) (90.3 +/- 0.02 vs. 84.6 +/- 0.01, p = 0.009), and overall RPE (15.5 +/- 0.5 vs. 14.4 +/- 0.5, p = 0.009), than during the 60TT. .V(O2) was not significantly different between the time trials; however, .V(CO2) (p = 0.008), ventilation (p = 0.004), and respiratory exchange ratio (p = 0.02) were significantly higher during the 30TT. Correlations were found between HR at LaT (r = 0.78), OBLA (r = 0.78), and Dmax (r = 0.71) for the 60TT, but not for the 30TT. These data suggest that despite a large variability in blood lactate during time trial efforts of 30 and 60 minutes (from 1.8 to 10.8 mmol.L(-1)), HR was consistently 90% of maximum for the 30TT and 85% for the 60TT. HR during the 30TT was approximated by HR corresponding to OBLA and Dmax, whereas HR during 60TT was approximated by LaT.     

Minimum time required for assessing step variability during running at submaximal velocities

This study aimed to determine the minimum time required for assessing spatiotemporal variability during continuous running at different submaximal velocities and, thereby, the number of steps required. Nineteen trained endurance runners performed an incremental running protocol, with a 3-min recording period at 10, 12, 14 and 16 km/h. Spatiotemporal parameters (contact and flight times, step length and step frequency) were measured using the OptoGait system and step variability was considered for each parameter, in terms of within-participants standard deviation (SD) and coefficient of variation (CV%). Step variability was considered over six different durations at every velocity tested: 0–10 s, 0–20 s, 0–30 s, 0–60 s, 0–120 s and 0–180 s. The repeated measures ANOVA revealed no significant differences in the magnitude of the four spatiotemporal parameters between the recording intervals at each running velocity tested (p ≥ 0.05, ICC > 0.90). The post-hoc analysis confirmed no significant differences in step variability (SD and CV% of each spatiotemporal parameter at any velocity tested) between measurements. The Bland-Altman limits of agreement method showed that longer recording intervals yield smaller systematic bias, random errors, and narrower limits of agreement, regardless of running velocity. The results suggest that the duration of the recording period required to estimate spatiotemporal variability plays an important role in the accuracy of the measurement, regardless of running velocity (10–16 km/h).