Verification of the heart rate threshold

Biomechanical, physiological and anthropometrical predictors of performance in recreational runners

Background

The maximal running speed (VMAX) determined on a graded treadmill test is well-recognized as a running performance predictor. However, few studies have assessed the variables that predict VMAX in recreationally active runners.

Methods

We used a mathematical procedure combining Fick's law and metabolic cost analysis to verify the relation between (1) VMAX versus anthropometric and physiological determinants of running performance and, (2) theoretical metabolic cost versus running biomechanical parameters. Linear multiple regression and bivariate correlation were applied. We aimed to verify the biomechanical, physiological, and anthropometrical determinants of VMAX in recreationally active runners. Fifteen recreationally active runners participated in this observational study. A Conconi and a stead-steady running test were applied using a heart rate monitor and a simple video camera to register the physiological and mechanical variables, respectively.

Results

Statistical analysis revealed that the speed at the second ventilatory threshold, theoretical metabolic cost, and fat-mass percentage confidently estimated the individual running performance as follows: VMAX = 58.632 + (-0.183 * fat percentage) + (-0.507 * heart rate percentage at second ventilatory threshold) + (7.959 * theoretical metabolic cost) (R2 = 0.62, p = 0.011, RMSE = 1.50 km.h-1). Likewise, the theoretical metabolic cost was significantly explained (R2 = 0.91, p = 0.004, RMSE = 0.013 a.u.) by the running spatiotemporal and elastic-related parameters (contact and aerial times, stride length and frequency, and vertical oscillation) as follows: theoretical metabolic cost = 10.421 + (4.282 * contact time) + (-3.795 * aerial time) + (-2.422 * stride length) + (-1.711 * stride frequency) + (0.107 * vertical oscillation).

Conclusion

Critical determinants of elastic mechanism, such as maximal vertical force and vertical and leg stiffness were unrelated to the metabolic economy. VMAX, a valuable marker of running performance, and its physiological and biomechanical determinants can be effectively evaluated using a heart rate monitor, treadmill, and a digital camera, which can be used in the design of training programs to recreationally active runners.

Electromyographic and Systemic Physiological Thresholds in Single-Joint Elbow Flexion Movements

PURPOSE

Reported relationships between electromyographic (EMG) thresholds and systemic thresholds based on lactate, ventilation, or heart rate are contradictory. This might be related to the complexity of the investigated whole-body movements involving many muscles with different activation patterns. Therefore, the aim of the study was to investigate these relationships during an incremental single-joint exercise.

METHODS

Eighteen male subjects (29.7 [4.4] y) performed single-arm elbow flexions on a biceps curl machine with loads increasing every minute until exhaustion. EMG signals of the main elbow flexors (short and long head of the biceps brachii, flexor carpi radialis, and brachioradialis) as well as gas exchange variables, blood lactate concentration, and heart rate were measured, and 2 turn points based on a 3-phase model of metabolism were determined for each variable.

RESULTS

The first and second turn points for EMG were determined at 32.0% to 33.1% and 64.4% to 66.5% of maximal achieved performance (maximum weight), respectively. Systemic turn points were determined at 33.3% to 34.4% and 65.9% to 66.7% of maximum weight and were not significantly different from EMG turn points. Furthermore, systemic and EMG turn points showed a strong or very strong relationship at the first (ρ = .54-.93, P < .05) and second turn point (ρ = .76-.93, P < .01).

CONCLUSIONS

A close relationship between EMG and systemic turn points could be confirmed for the applied movement of a small muscle group. The determination of local single muscle thresholds using EMG provides additional muscle-specific information about performance-limiting properties of muscles involved in endurance-type incremental exercise.

Heart rate dynamics during cardio-pulmonary exercise testing are associated with glycemic control in individuals with type 1 diabetes

INTRODUCTION

This study investigated the degree and direction (kHR) of the heart rate to performance curve (HRPC) during cardio-pulmonary exercise (CPX) testing and explored the relationship with diabetes markers, anthropometry and exercise physiological markers in type 1 diabetes (T1DM).

MATERIAL AND METHODS

Sixty-four people with T1DM (13 females; age: 34 ± 8 years; HbA1c: 7.8 ± 1% (62 ± 13 mmol.mol-1) performed a CPX test until maximum exhaustion. kHR was calculated by a second-degree polynomial representation between post-warm up and maximum power output. Adjusted stepwise linear regression analysis was performed to investigate kHR and its associations. Receiver operating characteristic (ROC) curve was performed based on kHR for groups kHR < 0.20 vs. > 0.20 in relation to HbA1c.

RESULTS

We found significant relationships between kHR and HbA1c (β = -0.70, P < 0.0001), age (β = -0.23, P = 0.03) and duration of diabetes (β = 0.20, P = 0.04). Stepwise linear regression resulted in an overall adjusted R2 of 0.57 (R = 0.79, P < 0.0001). Our data revealed also significant associations between kHR and percentage of heart rate at heart rate turn point from maximum heart rate (β = 0.43, P < 0.0001) and maximum power output relativized to bodyweight (β = 0.44, P = 0.001) (overall adjusted R2 of 0.44 (R = 0.53, P < 0.0001)). ROC curve analysis based on kHR resulted in a HbA1c threshold of 7.9% (62 mmol.mol-1).

CONCLUSION

Our data demonstrate atypical HRPC during CPX testing that were mainly related to glycemic control in people with T1DM.

Poor glycaemic control is associated with reduced exercise performance and oxygen economy during cardio-pulmonary exercise testing in people with type 1 diabetes

BACKGROUND

To explore the impact of glycaemic control (HbA_1c) on functional capacity during cardio-pulmonary exercise testing in people with type 1 diabetes.

METHODS

Sixty-four individuals with type 1 diabetes (age: 34 ± 8 years; 13 females, HbA_1c: 7.8 ± 1% (62 ± 13 mmol/mol), duration of diabetes: 17 ± 9 years) performed a cardio-pulmonary cycle ergometer exercise test until volitional exhaustion. Stepwise linear regression was used to explore relationships between HbA_1c and cardio-respiratory data with p ≤ 0.05. Furthermore, participants were divided into quartiles based on HbA_1c levels and cardio-respiratory data were analysed by one-way ANOVA. Multiple regression analysis was performed to explore the relationships between changes in time to exhaustion and cardio-respiratory data. Data were adjusted for confounder.

RESULTS

HbA_1c was related to time to exhaustion and oxygen consumption at the power output elicited at the sub-maximal threshold of the heart rate turn point (r = 0.47, R² = 0.22, p = 0.03). Significant differences were found at time to exhaustion between QI vs. QIV and at oxygen consumption at the power output elicited at the heart rate turn point between QI vs. QII and QI vs. QIV (p < 0.05). Changes in oxygen uptake, power output and in oxygen consumption at the power output elicited at the heart rate turn point and at maximum power output explained 55% of the variance in time to exhaustion (r = 0.74, R² = 0.55, p < 0.01).

CONCLUSIONS

Poor glycaemic control is related to less economical use of oxygen at sub-maximal work rates and an earlier time to exhaustion during cardio-pulmonary exercise testing. However, exercise training could have the same potential to counteract the influence of poor glycaemic control on functional capacity. Trial registration NCT01704417. Date of registration: October 11, 2012.

Graded Exercise Testing Protocols for the Determination of VO2max: Historical Perspectives, Progress, and Future Considerations

Graded exercise testing (GXT) is the most widely used assessment to examine the dynamic relationship between exercise and integrated physiological systems. The information from GXT can be applied across the spectrum of sport performance, occupational safety screening, research, and clinical diagnostics. The suitability of GXT to determine a valid maximal oxygen consumption (VO₂max) has been under investigation for decades. Although a set of recommended criteria exists to verify attainment of VO₂max, the methods that originally established these criteria have been scrutinized. Many studies do not apply identical criteria or fail to consider individual variability in physiological responses. As an alternative to using traditional criteria, recent research efforts have been directed toward using a supramaximal verification protocol performed after a GXT to confirm attainment of VO₂max. Furthermore, the emergence of self-paced protocols has provided a simple, yet reliable approach to designing and administering GXT. In order to develop a standardized GXT protocol, additional research should further examine the utility of self-paced protocols used in conjunction with verification protocols to elicit and confirm attainment of VO₂max.

Wearable Lactate Threshold Predicting Device is Valid and Reliable in Runners

Borges, NR and Driller, MW. Wearable lactate threshold predicting device is valid and reliable in runners. J Strength Cond Res 30(8): 2212-2218, 2016-A commercially available device claiming to be the world's first wearable lactate threshold predicting device (WLT), using near-infrared LED technology, has entered the market. The aim of this study was to determine the levels of agreement between the WLT-derived lactate threshold workload and traditional methods of lactate threshold (LT) calculation and the interdevice and intradevice reliability of the WLT. Fourteen (7 male, 7 female; mean ± SD; age: 18-45 years, height: 169 ± 9 cm, mass: 67 ± 13 kg, V[Combining Dot Above]O2max: 53 ± 9 ml·kg·min) subjects ranging from recreationally active to highly trained athletes completed an incremental exercise test to exhaustion on a treadmill. Blood lactate samples were taken at the end of each 3-minute stage during the test to determine lactate threshold using 5 traditional methods from blood lactate analysis which were then compared against the WLT predicted value. In a subset of the population (n = 12), repeat trials were performed to determine both inter-reliability and intrareliability of the WLT device. Intraclass correlation coefficient (ICC) found high to very high agreement between the WLT and traditional methods (ICC > 0.80), with TEMs and mean differences ranging between 3.9-10.2% and 1.3-9.4%. Both interdevice and intradevice reliability resulted in highly reproducible and comparable results (CV < 1.2%, TEM <0.2 km·h, ICC > 0.97). This study suggests that the WLT is a practical, reliable, and noninvasive tool for use in predicting LT in runners.

Interactive effects of body position and perceived exertion during spinning exercises

Spinning is a popular group exercise taught in health and fitness facilities worldwide. Throughout a Spinning workout session, intensity is variable and is controlled by body position on the Spinning stationary cycle and perceived resistance. This study examined the effects of 3 body positions and 4 levels of perceived exertion (RPE) on cardiorespiratory response and vastus lateralis normalized electromyographical activity (NrmsEMGVL). Eleven participants (24.4 ± 6.3 years) with 3.2 ± 2.2 years of Spinning experience completed twelve 3-minute randomly assigned Spinning conditions across 4 separate testing days after an 8-hour fast. Conditions were determined by body position (seated, running, and standing climb [SC]) and RPE (low, low-medium, medium-high, and high). Cardiorespiratory data and NrmsEMGVL were recorded continuously during each Spinning condition. Respiratory rate and oxygen consumption were significantly higher for running and SC than seated, and minute ventilation was significantly higher for running than seated. All cardiorespiratory values were higher at medium-high and high RPE, than low or medium-low RPE, and high RPE generated higher respiratory rate and respiratory exchange ratio than medium-high RPE. Significant body position × RPE interactions were observed for heart rate (HR) and NrmsEMGVL with running and SC producing higher HRs than seated at low and high RPE, and running producing higher NrmsEMGVL than seated at low RPE. Results indicate that running and SC provide the greatest cardiorespiratory responses, and maximal efforts are not needed for these responses. Additionally, HR seems to be a poor marker of oxygen consumption, especially at high RPEs.

Identification and agreement of first turn point by mathematical analysis applied to heart rate, carbon dioxide output and electromyography

Background

The second heart rate (HR) turn point has been extensively studied, however there are few studies determining the first HR turn point. Also, the use of mathematical and statistical models for determining changes in dynamic characteristics of physiological variables during an incremental cardiopulmonary test has been suggested.

Objectives

To determine the first turn point by analysis of HR, surface electromyography (sEMG), and carbon dioxide output () using two mathematical models and to compare the results to those of the visual method.

Method

Ten sedentary middle-aged men (53.9±3.2 years old) were submitted to cardiopulmonary exercise testing on an electromagnetic cycle ergometer until exhaustion. Ventilatory variables, HR, and sEMG of the vastus lateralis were obtained in real time. Three methods were used to determine the first turn point: 1) visual analysis based on loss of parallelism between and oxygen uptake (); 2) the linear-linear model, based on fitting the curves to the set of data (Lin-Lin ); 3) a bi-segmental linear regression of Hinkley' s algorithm applied to HR (HMM-HR), (HMM- ), and sEMG data (HMM-RMS).

Results

There were no differences between workload, HR, and ventilatory variable values at the first ventilatory turn point as determined by the five studied parameters (p>0.05). The Bland-Altman plot showed an even distribution of the visual analysis method with Lin-Lin , HMM-HR, HMM-CO_2, and HMM-RMS.

Conclusion

The proposed mathematical models were effective in determining the first turn point since they detected the linear pattern change and the deflection point of , HR responses, and sEMG.

Pontos de transição da frequência cardíaca em teste progressivo máximo

Foi realizada análise do comportamento da frequência cardíaca (FC) e identificação dos pontos de inflexão (PIFC) e de deflexão da FC (PDFC) em teste progressivo máximo, em sujeitos do sexo feminino e masculino. Vinte universitários foram submetidos ao teste em cicloergômetro. A FC foi monitorada para posterior análise e identificação dos pontos de transição (PT). A FC apresentou comportamento sigmóide, com identificação de PT em todos os sujeitos, sendo: a) em 65% PIFC (64 ± 27W; 29 ± 9%Pmáx e 126 ± 12bpm; 66 ± 5%FCmáx) e PDFC (177 ± 45W; 81 ± 10%Pmáx e 178 ± 8bpm; 93 ± 4%FCmáx); b) em 30% apenas PIFC (80 ± 32W; 36 ± 14%Pmáx e 125 ± 13bpm; 66 ± 5%FCmáx) e c) em 5% o PDFC isolado (103W; 57%Pmáx e 150bpm; 82%FCmáx). O PIFC foi encontrado em carga significativamente inferior ao PDFC, sem diferenças na carga e FC relativas entre os sexos.

Comparação do ponto de deflexão da frequência cardíaca com a máxima fase estável de lactato em corredores de fundo

O objetivo do estudo foi comparar o ponto de deflexão da freqüência cardíaca (PDFC) visual e método DMAX com a máxima fase estável de lactato (MFEL). Treze corredores executaram teste incremental Vameval e testes de cargas retangulares (TCR). A velocidade do PDFC visual (14,3 ± 1,13km.h-1) foi significantemente maior que o DMAX (13,2 ± 1,35km.h-1) além de apresentarem correlação não significante. Entretanto, nenhuma dessas velocidades foram diferentes da MFEL (13,8 ± 0,90km.h-1) embora somente o PDFC visual tenha apresentado correlação significante com a MFEL (r = 0,75). A concentração de lactato sanguíneo não apresentou estabilidade em oito sujeitos no TCR na intensidade do PDFC visual o qual nos leva a concluir que este não é um índice confiável para estimativa da MFEL. No entanto, este índice pode ser usado como um indicador de capacidade aeróbia.

Strong relationship between heart rate deflection point and ventilatory threshold in trained rowers

The purpose of this study was to assess the relationship between heart rate deflection point (HRDP) and ventilatory threshold (VT) to the physiological and performance variables in a relatively large group of trained men rowers. We proposed the hypothesis that physiological and performance variables corresponding to HRDP are not significantly different from corresponding variables at VT, which would justify the use of HRDP as a simple, affordable, and noninvasive method of anaerobic threshold assessment in trained rowers. Eighty-nine trained men rowers (mean ± SD: age 21.2 ± 4.1 years; stature 1.89 ± 0.06 m; body mass 89.2 ± 8.4 kg; VO₂max [maximum oxygen uptake] 5.39 ± 0.62 L/min⁻¹) completed an incremental rowing ergometer exercise test to exhaustion. Three independent, experienced observers determined both HRDP and VT. HRDP was determined by visual and computer-aided regression analyses and was evident in all rowers. The main findings include (a) there is a strong relationship among all observed physiological and performance variables corresponding to HR(HRDP) and HR(VT) (r = 0.79-0.96; p < 0.001) and (b) power output, oxygen uptake, ventilation, tidal volume and breathing rate corresponding to HR(HRDP) and HR(VT) were not significantly different (p ≥ 0.011), whereas HR(HRDP) was slightly but significantly higher than HR(VT) (174.5 vs. 172.8 beats·min⁻¹; p = 0.003). The standard error of the estimate in predicting the HR(VT) based on HR(HRDP) was 5.1 beats·min⁻¹. The subsequent data suggest that, in general, trained rowers may be able to periodically assess their aerobic endurance and evaluate the effects of training programs using the HRDP method.

Value of the Application of the Heart Rate Performance Curve in Sports

The heart rate performance curve (HRPC) has been shown to be nonlinearly related to work load. This phenomenon has been used to determine a defection point and to be related to the lactate anaerobic threshold. The original method was heavily criticized, and the method was challenged by several authors. However, some authors also demonstrated a high value for this method’s application in various sports conditions. Unfortunately, the HRPC was shown to be not uniform and three different patterns were found. Basic investigations have shown a dependence of the HR-defection on beta1-receptor sensitivity, which gave a plausible explanation of the phenomenon. Important details regarding the testing protocol and the method of turn point determination are given in this review. As a conclusion, we may state that based on numerous studies the method is plausible and valid to determine aerobic exercise performance in various laboratory ergometer and specific sports-related field conditions. Standard protocol conditions adjusted to the exercise performance level of subjects and a computer-supported determination of turn points are necessary to obtain reliable results. Large-scale investigations to validate the heart rate turn point with maximal lactate steady state are still needed. However, from the available literature, the application of this noninvasive method can be recommended to determine aerobic exercise performance in various sports. This noninvasive test is easy to perform repeatedly, which gives interesting possibilities for the monitoring of training adaptation in the short term, such as altitude training or specifc taper forms.

Sustained, prolonged exercise at stable heart rate defined by the deflection point identification method

Gripp,The objectives of this study were to identify the heart rate deflection point (HRDP) assessed according to the Conconi test method, to evaluate the ability of trained cyclists to pedal for 90 minutes while remaining within a stable heart rate (HR) range determined by identifying the HRDP, and to discuss the motor and physiological parameters recorded during this long-duration exercise. Ten trained men cyclists (VO2max: 64.1 +/- 8.86 mlxkgxmin) had their HRDPs determined. One week later, they performed continuous exercise for 90 minutes on a cycle ergometer at a stable HR sustained within a range comprising the HRDP +/- 5 bpm. Subjects' HR and power output values were registered at each minute. Blood lactate, blood glucose, and body temperature were measured at rest and during exercise. All exercise was performed inside an environmental chamber (temperature of 22 degrees C, relative humidity of 60%). In the first 5 minutes, the participants increased power output to reach the HRDP, and adjustments were required in their physiological parameters to meet this exercise demand. Between the 5th and the 30th minutes, HRDP had already been reached by all participants; nevertheless, all the other physiological and motor parameters were adjusting to this exercise demand. After 30 minutes of exercise, the physiological and motor variables had already adjusted to the new demand and remained stable until the end of exercise (blood lactate was not significantly different from 4 mmolxL). These results suggest the efficacy of the HRDP as an auxiliary method for prescribing and controlling sport training: after the defined HRDP has been reached, the technique confirms maintenance of power output, as well as the other physiological parameters, at threshold levels until the end of exercise.

A single exercise test for assessing physiological and performance parameters in elite rowers: the 2-in-1 test

Testing to determine blood lactate thresholds for prescription of rowing training is usually conducted separately from performance testing (i.e. 2000m time trial). The purpose of this study was to investigate whether the testing required to determine blood lactate thresholds and performance in elite rowers could be reduced by undertaking a single test combining incremental exercise with a 2000m time trial. Ten elite rowers (age 20.9+/-2.1 years, mean+/-S.D.) performed, on separate occasions and in random order, an incremental seven-step rowing test (INCR), a 2000m time trial (2k), or a combined test involving the performance of six incremental submaximal workloads followed by 15min of recovery and then a 2000m time trial (2-in-1). Physiological and performance parameters (blood lactate thresholds, accumulated oxygen deficit, heart rate, work parameters) determined during 2-in-1 were not significantly different from those determined during INCR or 2k, except for peak oxygen uptake which was higher during 2-in-1 compared with INCR (4.23+/-0.22 versus 4.14+/-0.20lmin(-1), p=0.02), and peak rating of perceived exertion which was lower during 2-in-1 compared with INCR (19.4+/-0.2 versus 19.9+/-0.1, p=0.02). We conclude that physiological and performance parameters that have traditionally been assessed during separate incremental exercise and 2000m time trial testing in elite rowers can be validly determined during a single combined exercise test.

Comparison of anaerobic threshold determined by visual and mathematical methods in healthy women

Several methods are used to estimate anaerobic threshold (AT) during exercise. The aim of the present study was to compare AT obtained by a graphic visual method for the estimate of ventilatory and metabolic variables (gold standard), to a bi-segmental linear regression mathematical model of Hinkley's algorithm applied to heart rate (HR) and carbon dioxide output (VCO2) data. Thirteen young (24 +/- 2.63 years old) and 16 postmenopausal (57 +/- 4.79 years old) healthy and sedentary women were submitted to a continuous ergospirometric incremental test on an electromagnetic braking cycloergometer with 10 to 20 W/min increases until physical exhaustion. The ventilatory variables were recorded breath-to-breath and HR was obtained beat-to-beat over real time. Data were analyzed by the nonparametric Friedman test and Spearman correlation test with the level of significance set at 5%. Power output (W), HR (bpm), oxygen uptake (VO2; mL kg(-1) min(-1)), VO2 (mL/min), VCO2 (mL/min), and minute ventilation (VE; L/min) data observed at the AT level were similar for both methods and groups studied (P > 0.05). The VO2 (mL kg(-1) min(-1)) data showed significant correlation (P < 0.05) between the gold standard method and the mathematical model when applied to HR (rs = 0.75) and VCO2 (rs = 0.78) data for the subjects as a whole (N = 29). The proposed mathematical method for the detection of changes in response patterns of VCO2 and HR was adequate and promising for AT detection in young and middle-aged women, representing a semi-automatic, non-invasive and objective AT measurement.

Comparison of the influence of different rehabilitation programmes on clinical, spirometric and spiroergometric parameters in patients with multiple sclerosis

PURPOSE

The aim of this study was to compare the effect of four different programmes on spiroergometric, spirometric and clinical parameters in multiple sclerosis (MS) patients.

METHODS

One hundred and twelve MS patients were divided into four groups. The first group underwent neurophysiologically based physiotherapy, the second aerobic training, the third combined therapy (neurophysiologically based physiotherapy and aerobic training) and the fourth did not change any habits. Seventeen patients did not finish the study. Patients were examined on impairment (Expanded Disability Status Scale), disability (Barthel Index), handicap (Environment Status Scale), quality of life (Multiple Sclerosis Quality of Life), fatigue (Modified Fatigue Impact Scale), depression (Beck Depression Inventory Score), respiratory function (spirometric parameters on spirometry) and physical fitness (spiroergometric parameters on a bicycle ergometer).

RESULTS

The patients who participated in one of our training programmes showed a significant improvement of the examined parameters in comparison to those who did not change their present habits. Each of the four training programmes had a different impact on the parameters, which means that each of them had a different effect. The neurophysiologically based physiotherapy had the greatest impact on impairment, and the aerobic training on spirometric and spiroergometric parameters. All methods (the neurophysiologically based physiotherapy, the aerobic training and the combined programme) had an impact on fatigue.

Beta1-adrenoceptor mediated origin of the heart rate performance curve deflection

PURPOSE

The deflection of the HR performance curve (HRPC) has been described as an objective marker of submaximal exercise performance. HR response to incremental cycle ergometer exercise is shown to be neither linear nor uniform and a physiological explanation of the deflection phenomenon is lacking. We hypothesized that differences in the beta1-adrenoceptor site are the source of these differences. The aim of the study was to investigate the influence of the highly selective beta1-adrenoceptor (beta1-AR) antagonist bisoprolol (Bi) on the HRPC in young healthy male subjects with different HR response patterns.

METHODS

Sixteen subjects were treated in randomized order with Bi or a placebo (Pl) in two separate trials. HR response during incremental cycle ergometer exercise was compared between the two trials. Blood lactate concentration (La) and ventilatory variables were measured throughout both tests.

RESULTS

Bi changed the direction of the HRPC more in subjects with a regular, s-shaped response pattern under placebo than those with a nonregular or linear pattern. The influence of Bi on the HR at the second lactate turn point was significantly related (R = 0.78; P < 0.001) to the pattern of the HRPC in Pl conditions.

CONCLUSION

We suggest that differences between the subjects with regular s-shaped versus nonregular HRPC may be due to differences at the beta1-AR site. The origin of the HRPC deflection is mediated in part by the beta1-AR sensitivity.

Is lactic acidosis a cause of exercise induced hyperventilation at the respiratory compensation point?

OBJECTIVES

The respiratory compensation point (RCP) marks the onset of hyperventilation ("respiratory compensation") during incremental exercise. Its physiological meaning has not yet been definitely determined, but the most common explanation is a failure of the body's buffering mechanisms which leads to metabolic (lactic) acidosis. It was intended to test this experimentally.

METHODS

During a first ramp-like exercise test on a cycle ergometer, RCP (range: 2.51-3.73 l x min(-1) oxygen uptake) was determined from gas exchange measurements in five healthy subjects (age 26-42; body mass index (BMI) 20.7-23.9 kg x m(-2); Vo(2peak) 51.3-62.1 ml x min(-1) x kg(-1)). On the basis of simultaneous determinations of blood pH and base excess, the necessary amount of bicarbonate to completely buffer the metabolic acidosis was calculated. This quantity was administered intravenously in small doses during a second, otherwise identical, exercise test.

RESULTS

In each subject sufficient compensation for the acidosis, that is, a pH value constantly above 7.37, was attained during the second test. A delay but no disappearance of the hyperventilation was present in all participants when compared with the first test. RCP occurred on average at a significantly (p = 0.043) higher oxygen uptake (+0.15 l x min(-1)) compared with the first test.

CONCLUSIONS

For the first time it was directly demonstrated that exercise induced lactic acidosis is causally involved in the hyperventilation which starts at RCP. However, it does not represent the only additional stimulus of ventilation during intense exercise. Muscle afferents and other sensory inputs from exercising muscles are alternative triggering mechanisms.

A review of the concept of the heart rate deflection point

The heart rate deflection point (HRDP) is a downward or upward change from the linear HR-work relationship evinced during progressive incremental exercise testing. The HRDP is reported to be coincident with the anaerobic threshold. In 1982, Conconi and colleagues suggested that this phenomenon could be used as a noninvasive method to assess the anaerobic threshold. These researchers developed a field test to assess the HRDP, which has become popularised as the 'Conconi test'. Concepts used to define and assess the anaerobic threshold as well as methodological procedures used to determine the HRDP are diverse in the literature and have contributed to controversy surrounding the HRDP concept. Although the HRDP may be assessed in either field or laboratory settings, the degree of HR deflection is highly dependent upon the type of protocol used. The validity of HRDP to assess the anaerobic threshold is uncertain, although a high degree of relationship exists between HRDP and the second lactate turnpoint. The HRDP appears to be reliable when a positive identification is made; however, not all studies report 100% reproducibility. Although the physiological mechanisms explaining the HRDP are unresolved, a relationship exists between the degree and direction of HRDP and left ventricular function. The HRDP has potential to be used for training regulation purposes. Clinically, it may be incorporated to set exercise intensity parameters for cardiac rehabilitation.

Heart dimensions may influence the occurrence of the heart rate deflection point in highly trained cyclists

OBJECTIVES

To determine whether the heart rate (HR) response to exercise in 21 highly trained cyclists (mean (SD) age 25 (3) years) was related to their heart dimensions.

METHODS

Before performing an incremental exercise test involving a ramp protocol with workload increases of 25 W/min, each subject underwent echocardiographic evaluation of the following variables: left ventricular end diastolic internal diameter (LVIDd), left ventricular posterior wall thickness at end diastole (LVPWTd), interventricular septal wall thickness at end diastole (IVSTd), left ventricular mass index (LVMI), left atrial dimension (LAD), longitudinal left atrial (LLAD) and right atrial (LRAD) dimensions, and the ratio of early to late (E/A) diastolic flow velocity.

RESULTS

The HR response showed a deflection point (HRd) at about 85% VO2MAX in 66.7% of subjects (D group; n = 14) and was linear in 33.3% (NoD group; n = 7). Several echocardiographic variables (LVMI, LAD, LLAD, LRAD) indicative of heart dimensions were similar in each group. However, mean LPWTd (p<0.01) and IVSTd (p<0.05) values were significantly higher in the D group. Finally, no significant difference between groups was found with respect to the E/A.

CONCLUSIONS

The HR response is curvilinear during incremental exercise in a considerable number of highly trained endurance athletes-that is, top level cyclists. The departure of HR increase from linearity may predominantly occur in athletes with thicker heart walls.

Analysis of the aerobic-anaerobic transition in elite cyclists during incremental exercise with the use of electromyography

OBJECTIVES

To investigate the validity and reliability of surface electromyography (EMG) as a new non-invasive determinant of the metabolic response to incremental exercise in elite cyclists. The relation between EMG activity and other more conventional methods for analysing the aerobic-anaerobic transition such as blood lactate measurements (lactate threshold (LT) and onset of blood lactate accumulation (OBLA)) and ventilatory parameters (ventilatory thresholds 1 and 2 (VT1 and VT2)) was studied.

METHODS

Twenty eight elite road cyclists (age 24 (4) years; VO2MAX 69.9 (6.4) ml/kg/min; values mean (SD)) were selected as subjects. Each of them performed a ramp protocol (starting at 0 W, with increases of 5 W every 12 seconds) on a cycle ergometer (validity study). In addition, 15 of them performed the same test twice (reliability study). During the tests, data on gas exchange and blood lactate levels were collected to determine VT1, VT2, LT, and OBLA. The root mean squares of EMG signals (rms-EMG) were recorded from both the vastus lateralis and the rectus femoris at each intensity using surface electrodes.

RESULTS

A two threshold response was detected in the rms-EMG recordings from both muscles in 90% of subjects, with two breakpoints, EMGT1 and EMGT2, at around 60-70% and 80-90% of VO2MAX respectively. The results of the reliability study showed no significant differences (p > 0.05) between mean values of EMGT1 and EMGT2 obtained in both tests. Furthermore, no significant differences (p > 0.05) existed between mean values of EMGT1, in the vastus lateralis and rectus femoris, and VT1 and LT (62.8 (14.5) and 69.0 (6.2) and 64.6 (6.4) and 68.7 (8.2)% of VO2MAX respectively), or between mean values of EMGT2, in the vastus lateralis and rectus femoris, and VT2 and OBLA (86.9 (9.0) and 88.0 (6.2) and 84.6 (6.5) and 87.7 (6.4)% of VO2MAX respectively).

CONCLUSION

rms-EMG may be a useful complementary non-invasive method for analysing the aerobic-anaerobic transition (ventilatory and lactate thresholds) in elite cyclists.

Assessment of long-distance running performance in elite male runners using onset of blood lactate accumulation

The purpose of this study was to evaluate the relationship between onset of blood lactate accumulation (OBLA) and long-distance running performance in order to examine whether OBLA can be a good predictor of long-distance running performance even in elite male runners with similar performance levels. Eleven highly-trained male long-distance runners participated in this study. The average running velocities of the individuals' running performance were 5.918 +/- 0.084 m.s-1 and 5.672 +/- 0.095 m.s-1 for 5000 m (V5000) and 10,000 m (V10000), respectively. The blood lactate concentrations and heart rate responses were measured immediately after field running, and the average value of running velocity corresponding to OBLA (VOBLA) was 5.447 +/- 0.132 m.s-1. Variations of these three velocities expressed as a coefficient of variance (CV) ranged from 1.4 to 2.4%. A strong inverse relationship between heart rate corresponding to OBLA (HROBLA) and performance was observed (r = -0.709, p < 0.02 for V5000 and r = -0.830, p < 0.01 for V10000), while there was a lack of significant relationship between VOBLA and performance (r = 0.293, NS for V5000 and r = 0.130, NS for V10000). Furthermore, the average value of HROBLA obtained in this study (174.5 +/- 8.2 b.min-1) was quite similar to that of the heart rate threshold reported by some previous researchers. In conclusion, VOBLA alone could not explain the small variation of long-distance running performance, and HROBLA should be used in place of VOBLA for evaluating long-distance running performance in elite runners with quite similar performance levels.

The anaerobic threshold in cystic fibrosis: comparison of V-slope method, lactate turn points, and Conconi test

Physical exercise can improve sputum clearance in patients with cystic fibrosis (CF). To set up individual training protocols it is desirable to know the anaerobic threshold (AT). Established methods such as blood lactate measurements and ergometry can only be performed in specialized centers. Conconi showed that the heart rate threshold (HRT), i.e., the deflection point from the linear relationship between work load and heart rate, correlated significantly with the AT in healthy adults. To assess the reliability of the HRT in CF, we performed ergometry in 32 CF patients (mean age, 21.0 +/- 5.5 years; mean Shwachman score, 77.8 +/- 12.0) according to the Conconi protocol. The HRT was compared with the aerobic threshold (AeT) as determined by the V-slope method and with two turn points in the lactate performance curve (LTP1, LTP2). An HRT could be obtained in only 17 of the 32 patients (53%). In these 17 patients there was a significant correlation between HRT and the other thresholds, but the absolute values for the AT differed considerably: The mean HRT was 132% higher than the AeT according to Beaver, 107% higher than LTP1, and 19% higher than LTP2. Exercise protocols that rely solely on the HRT in CF will lead to excessive exertion during exercise training programs in these patients. According to these results the HRT of Conconi is not a suitable method to determine appropriate exercise levels in CF training programs and might even be harmful in CF patients. These results also indicate the need to test the reliability of a diagnostic procedure that has been developed only for healthy people.

The Conconi test in not valid for estimation of the lactate turnpoint in runners

Conconi et al. (1982) reported that an observed deviation from linearity in the heart rate-running velocity relationship determined during a field test in runners coincided with the 'lactate threshold'. The aim of this study was to assess the validity of the original Conconi test using conventional incremental and constant-load laboratory protocols. Fourteen trained male distance runners (mean +/-s: age 22.6 +/- 3.4 years; body mass 67.6 +/- 4.8 kg; peak VO2 66.3 +/- 4.7 ml kg-1 min-1) performed a standard multi-stage test for determination of lactate turnpoint and a Conconi test on a motorized treadmill. A deviation from linearity in heart rate was observed in nine subjects. Significant differences were found to exist between running velocity at the lactate turnpoint (4.39 +/- 0.20 m s-1) and at deviation from linear heart rate (5.08 +/- 0.25 m s-1) (P < 0.01), and between heart rate at the lactate turnpoint (172 +/- 10 beats min-1) and at deviation from linearity (186 +/- 9 beats min-1) (P < 0.01). When deviation of heart rate from linearity was evident, it occurred at a systematically higher intensity than the lactate turnpoint and at approximately 95% of maximum heart rate. These results were confirmed by the physiological responses of seven subjects, who performed two constant-velocity treadmill runs at 0.14 m s-1 below the running velocity at the lactate turnpoint and that at which the heart rate deviated from linearity. For the lactate turnpoint trial, the prescribed 30 min exercise period was completed by all runners (terminal blood lactate concentration of 2.4 +/- 0.5 mM), while the duration attained in the trial for which heart rate deviated from linearity was 15.9 +/- 6.7 min (terminal blood lactate concentration of 8.1 +/- 1.8 mM). We concluded that the Conconi test is invalid for the non-invasive determination of the lactate turnpoint and that the deviation of heart rate from linearity represents the start of the plateau at maximal heart rate, the expression of which is dependent upon the specifics of the Conconi test protocol.

Heart rate performance curve during incremental cycle ergometer exercise in healthy young male subjects

In 1992 Conconi et al. (20) presented an indirect and noninvasive method for the determination of anaerobic threshold (AnT) in an incremental field test for runners. This noninvasive method for the determination of anaerobic threshold is dependent on the occurrence of a deflection of the heart rate performance curve (HRPC). The aim of our study was to evaluate the degree and direction of the deflection of the HRPC and the relationship of the heart rate threshold (HRT) to the lactate turn point in a group of 227 healthy young subjects (age: 23 +/- 4 yr). The subjects were divided into three groups by means of second degree polynomial fitting (GI: regular deflection, kHR > 0.1; G II: no deflection, 0 < kHR < 0.1; G II: inverse deflection, k < -0.1). No significant differences between the groups were found in the anthropometric data or in the power output and the blood lactate concentration at both the first (LTP1) and second (LTP2) lactate turn points and at maximum performance (Pmax). Using the method of Conconi et al. (20), 85.9% of the subjects showed a "regular" deflection, 6.2% showed no deflection at all, and 7.9% showed even an inverted deflection of the HRPC. An HRT could be obtained in both G I and G III, and power output at HRT was not significantly different in comparison to that at the LTP2. No HRT could be assessed in G II. The heart rate at HRT and the LTP2 were significantly lower in G III compared with G I. The phenomenon of heart rate break point may be attractive in training regulation, but its application is limited because a heart rate deflection cannot be found even in young subjects in some cases.