Effect of endurance training on blood lactate clearance after maximal exercise

Can Wearable Sweat Lactate Sensors Contribute to Sports Physiology?

The rise of wearable sensors to measure lactate content in human sweat during sports activities has attracted the attention of physiologists given the potential of these “analytical tools” to provide real-time information. Beyond the assessment of the sensing technology per se, which, in fact, has not rigorously been validated yet in controlled conditions, there are many open questions about the true usefulness of such wearable sensors in real scenarios. On the one hand, the evidence for the origin of sweat lactate (e.g., via the sweat gland, derivation from blood, or other alternative mechanisms), its high concentration (1–25 mM or even higher) compared to levels in the blood, and the possible correlation between different biofluids (particularly blood) is rather contradictory and generates vivid debate in the field. On the other hand, it is important to point out that accurate detection of sweat lactate is highly dependent on the procedure used to collect and/or reach the fluid, and this can likely explain the large discrepancies reported in the literature. In brief, this paper provides our vision of the current state of the field and a thoughtful evaluation of the possible reasons for present controversies, together with an analysis of the impact of wearable sweat lactate sensors in the physiological context. Finally, although there is not yet overwhelming scientific evidence to provide an unequivocal answer to whether wearable sweat lactate sensors can contribute to sports physiology, we still understand the importance to bring this challenging question up-front to create awareness and guidance in the development, validation, and implementation of wearable sensors.

Traditional and quantitative analysis of acid-base and electrolyte imbalances in horses competing in cross-country competitions at 2-star to 5-star level

Background

Early recognition and management of acid‐base, fluid, and electrolyte disorders are crucial for the maintenance of health and performance in equine athletes.

Objectives

To analyze changes in acid‐base and electrolyte status associated with exercise during cross‐country competitions at different levels using traditional and quantitative approaches.

Animals

Thirty‐eight eventing horses.

Methods

Prospective observational study. Jugular venous blood samples were collected before and after the cross‐country test of 25 international eventing competitions ranging from 2‐star (formerly 1‐star) to 5‐star (formerly 4‐star) level. Blood gas analysis was performed to determine pH, pCO₂, Na⁺, Cl⁻, and K⁺ and calculate HCO₃⁻, tCO₂ base excess (BE_ECF), anion gap (AG), strong ion difference calculated from Na⁺, K⁺, Cl⁻, and lactate⁻ (SID₄), strong ion difference calculated from Na⁺, K⁺, and Cl⁻ (SID₃), strong ion gap (SIG), and total nonvolatile weak buffer concentration (A_tot). Postexercise acid‐base imbalances, diagnosed on the basis of the traditional approach, and the simplified strong ion model were compared.

Results

Significant decreases in pH, Cl⁻, SID₄, pCO₂, HCO₃⁻, tCO₂, and BE_ECF as well as increases in K⁺, SID₃, AG, TP, and A_tot were observed between pre‐ and postexercise samples. The changes in acid‐base parameters were significantly affected by the competition level. Using the strong ion approach, a higher proportion of horses was diagnosed with postexercise metabolic acidosis.

Conclusions and Clinical Importance

Regarding the complex acid‐base changes in horses competing at cross‐country competitions, the quantitative approach provided a more detailed analysis of the different factors contributing to acid‐base balance than did the traditional approach.

Is the Functional Threshold Power a Valid Surrogate of the Lactate Threshold?

PURPOSE

To analyze the relationship between functional threshold power (FTP) and the lactate threshold (LT).

METHODS

A total of 20 male cyclists performed an incremental test in which LT was determined. At least 48 h later, they performed a 20-min time trial, and 95% of the mean power output was defined as FTP. Participants were divided into recreational (peak power output < 4.5 W·kg-1; n = 11) or trained cyclists (peak power output > 4.5 W·kg-1; n = 9) according to their fitness status.

RESULTS

The FTP (240 [35] W) was overall not significantly different (effect size = 0.20; limits of agreement = -2.4% [11.5%]) from the LT (246 [24] W), and both markers were strongly correlated (r = .95; P < .0001). Accounting for the participants' fitness status, no significant differences were found between FTP and LT (effect size = 0.22; limits of agreement =2.1% [7.8%]) in trained cyclists, but FTP was significantly lower than the LT (P = .0004, effect size = 0.81; limits of agreement =-6.5% [8.3%]) in recreational cyclists. A significant relationship was found between relative peak power output and the bias between FTP and the LT markers (r = .77; P < .0001).

CONCLUSIONS

FTP is a valid field test-based marker for the assessment of endurance fitness. However, caution should be taken when using FTP interchangeably with LT, as the bias between markers seems to depend on the athlete's fitness status. Whereas FTP provides a good estimate of LT in trained cyclists, in recreational cyclists, it may underestimate LT.

Exercise duration and blood lactate concentrations following high intensity cycle ergometry

The aim of this study was to investigate differences in blood lactate accumulation following 10 and 20 sec of maximal cycle ergometer exercise. Body mass, stature, and age of the group was determined prior to testing (82.57 ± 5.94 kg 177 ± 5.94 cm and 21.42 ± 1.61 yrs, respectively). Eight male rugby union players performed two maximal sprints in a random fashion of 10 and 20 sec duration on a cycle ergometer. During the 10 and 20 sec trial, blood lactate levels measured were as follows 1.58 ± 0.78, 4.43 ± 1.4, and 3.5 ± 1.2 mmol.l⁻¹ vs. 1.72 ± 0.65, 6.14 ± 2, and 5.68 ± 2.22 mmol.l⁻¹, respectively. Differences were found (P < 0.01) from rest to 5 and 10 min postexercise in both groups. Differences in concentration also were found between groups at both postexercise stages (P < 0.01). The reduction in blood lactate concentrations observed between the 5 to 10 min recovery stages were 0.91 ± 0.58 mmol.l⁻¹ vs. 0.46 ± 0.48 mmol.l⁻¹ following 10 and 20 sec of maximal exercise, respectively (P > 0.05). The concentrations observed are interesting and may influence recovery time and subsequent exercise performance.

Metabolic Consequences of Resistive Force Selection During Cycle Ergometry Exercise

The purpose of this study was to compare power outputs and blood lactate concentrations ([La-]B) following 30 s of maximal cycle ergometry when resistive forces were derived from total-body mass (TBM) or fat-free mass (FFM). Differences (P < 0.05) in peak power output (PPO), pedal velocity (PV) and resistive forces (RF) were observed when the TBM and FFM protocols were compared (953 +/- 114 W vs. 1020 +/- 134 W; 134 +/- 8 rpm vs. 141 +/- 7 rpm; 6 +/- 1 kg vs. 5 +/- 1 kg, respectively). Blood lactate values ([La-]B) increased (P < 0.01) postexercise for both protocols and were significantly greater for TBM (10.6 +/- 1.2 mmol.l-1 vs 11.6 +/- 1.1 mmol.l-1, P < 0.05). These findings indicate that the FFM resistive force protocol may maximise adenosinotriphosphate-phosphocreatine (ATP-PC) utilisation with smaller contributions from anaerobic glycolysis when compared with TBM. These results may have important implications in the assessment of high intensity exercise performance.

Multiple sprint work : physiological responses, mechanisms of fatigue and the influence of aerobic fitness

The activity patterns of many sports (e.g. badminton, basketball, soccer and squash) are intermittent in nature, consisting of repeated bouts of brief (<or=6-second) maximal/near-maximal work interspersed with relatively short (<or=60-second) moderate/low-intensity recovery periods. Although this is a general description of the complex activity patterns experienced in such events, it currently provides the best means of directly assessing the physiological response to this type of exercise. During a single short (5- to 6-second) sprint, adenosine triphosphate (ATP) is resynthesised predominantly from anaerobic sources (phosphocreatine [PCr] degradation and glycolysis), with a small (<10%) contribution from aerobic metabolism. During recovery, oxygen uptake (V-O2) remains elevated to restore homeostasis via processes such as the replenishment of tissue oxygen stores, the resynthesis of PCr, the metabolism of lactate, and the removal of accumulated intracellular inorganic phosphate (Pi). If recovery periods are relatively short, V-O2 remains elevated prior to subsequent sprints and the aerobic contribution to ATP resynthesis increases. However, if the duration of the recovery periods is insufficient to restore the metabolic environment to resting conditions, performance during successive work bouts may be compromised. Although the precise mechanisms of fatigue during multiple sprint work are difficult to elucidate, evidence points to a lack of available PCr and an accumulation of intracellular Pi as the most likely causes. Moreover, the fact that both PCr resynthesis and the removal of accumulated intracellular Pi are oxygen-dependent processes has led several authors to propose a link between aerobic fitness and fatigue during multiple sprint work. However, whilst the theoretical basis for such a relationship is compelling, corroborative research is far from substantive. Despite years of investigation, limitations in analytical techniques combined with methodological differences between studies have left many issues regarding the physiological response to multiple sprint work unresolved. As such, multiple sprint work provides a rich area for future applied sports science research.

Training techniques to improve endurance exercise performances

In previously untrained individuals, endurance training improves peak oxygen uptake (VO2peak), increases capillary density of working muscle, raises blood volume and decreases heart rate during exercise at the same absolute intensity. In contrast, sprint training has a greater effect on muscle glyco(geno)lytic capacity than on muscle mitochondrial content. Sprint training invariably raises the activity of one or more of the muscle glyco(geno)lytic or related enzymes and enhances sarcolemmal lactate transport capacity. Some groups have also reported that sprint training transforms muscle fibre types, but these data are conflicting and not supported by any consistent alteration in sarcoplasmic reticulum Ca2+ ATPase activity or muscle physicochemical H+ buffering capacity. While the adaptations to training have been studied extensively in previously sedentary individuals, far less is known about the responses to high-intensity interval training (HIT) in already highly trained athletes. Only one group has systematically studied the reported benefits of HIT before competition. They found that >or=6 HIT sessions, was sufficient to maximally increase peak work rate (W(peak)) values and simulated 40 km time-trial (TT(40)) speeds of competitive cyclists by 4 to 5% and 3.0 to 3.5%, respectively. Maximum 3.0 to 3.5% improvements in TT(40) cycle rides at 75 to 80% of W(peak) after HIT consisting of 4- to 5-minute rides at 80 to 85% of W(peak) supported the idea that athletes should train for competition at exercise intensities specific to their event. The optimum reduction or 'taper' in intense training to recover from exhaustive exercise before a competition is poorly understood. Most studies have shown that 20 to 80% single-step reductions in training volume over 1 to 4 weeks have little effect on exercise performance, and that it is more important to maintain training intensity than training volume. Progressive 30 to 75% reductions in pool training volume over 2 to 4 weeks have been shown to improve swimming performances by 2 to 3%. Equally rapid exponential tapers improved 5 km running times by up to 6%. We found that a 50% single-step reduction in HIT at 70% of W(peak) produced peak approximately 6% improvements in simulated 100 km time-trial performances after 2 weeks. It is possible that the optimum taper depends on the intensity of the athletes' preceding training and their need to recover from exhaustive exercise to compete. How the optimum duration of a taper is influenced by preceding training intensity and percentage reduction in training volume warrants investigation.

Interval training for performance: a scientific and empirical practice. Special recommendations for middle- and long-distance running. Part II: anaerobic interval training

Studies of anaerobic interval training can be divided into 2 categories. The first category (the older studies) examined interval training at a fixed work-rate. They measured the time limit or the number of repetitions the individual was able to sustain for different pause durations. The intensities used in these studies were not maximal but were at about 130 to 160% of maximal oxygen uptake (VO2max). Moreover, they used work periods of 10 to 15 seconds interrupted by short rest intervals (15 to 40 seconds). The second category (the more recent studies) asked the participants to repeat maximal bouts with different pause durations (30 seconds to 4 to 5 minutes). These studies examined the changes in maximal dynamic power during successive exercise periods and characterised the associated metabolic changes in muscle. Using short-interval training, it seems to be very difficult to elicit exclusively anaerobic metabolism. However, these studies have clearly demonstrated that the contribution of glycogenolysis to the total energy demand was considerably less than that if work of a similar intensity was performed continuously. However, the latter studies used exercise intensities that cannot be described as maximal. This is the main characteristic of the second category of interval training performed above the minimal velocity associated with VO2max determined in an incremental test (vVO2max). Many studies on the long term physiological effect of supramaximal intermittent exercise have demonstrated an improvement in VO2max or running economy.