Estimating Hemodynamic Responses to the Wingate Test Using Thoracic Impedance

Techniques including direct Fick and Doppler echocardiography are frequently used to assess hemodynamic responses to exercise. Thoracic impedance has been shown to be a noninvasive alternative to these methods for assessing these responses during graded exercise to exhaustion, yet its feasibility during supramaximal bouts of exercise is relatively unknown. We used thoracic impedance to estimate stroke volume (SV) and cardiac output (CO) during the Wingate test (WAnT) and compared these values to those from graded exercise testing (GXT). Active men (n = 9) and women (n = 7) (mean age = 24.8 ± 5.9 yr) completed two Wingate tests and two graded exercise tests on a cycle ergometer. During exercise, heart rate (HR), SV, and CO were continuously estimated using thoracic impedance. Repeated measures analysis of variance was used to identify potential differences in hemodynamic responses across protocols. Results: Maximal SV (138.6 ± 37.4 mL vs. 135.6 ± 26.9 mL) and CO (24.5 ± 6.1 L·min^-1 vs. 23.7 ± 5.1 L·min^-1) were similar (p > 0.05) between repeated Wingate tests. Mean maximal HR was higher (p < 0.01) for GXT (185 ± 7 b·min^-1) versus WAnT (177 ± 11 b·min^-1), and mean SV was higher in response to WAnT (137.1 ± 32.1 mL) versus GXT (123.0 ± 32.0 mL), leading to similar maximal cardiac output between WAnT and GXT (23.9 ± 5.6 L·min^-1 vs. 22.5 ± 6.0 L·min^-1). Our data show no difference in hemodynamic responses in response to repeated administrations of the Wingate test. In addition, the Wingate test elicits similar cardiac output compared to progressive cycling to VO₂max.

Key points

• Measurement of cardiac output (CO), the rate of oxygen transport delivered by the heart to skeletal muscle, is not widely-employed in Exercise Physiology due to the level of difficulty and invasiveness characteristic of most techniques used to measure this variable.
• Nevertheless, thoracic impedance has been shown to provide a noninvasive and simpler approach to continuously measure CO at rest and during exercise.
• Results show that measurements of CO are not different and highly reliable in response to repeated administrations of the Wingate test.
• Despite vastly different intensities and durations, maximal CO was similar between the Wingate test and graded exercise to VO₂max.

Key words: Stroke volume, cardiac output, cycle ergometer, maximal oxygen uptake, supramaximal exercise     

Comparing Fat Oxidation in an Exercise Test with Moderate-Intensity Interval Training

This study compared fat oxidation rate from a graded exercise test (GXT) with a moderate-intensity interval training session (MIIT) in obese men. Twelve sedentary obese males (age 29 ± 4.1 years; BMI 29.1 ± 2.4 kg·m^-2; fat mass 31.7 ± 4.4 %body mass) completed two exercise sessions: GXT to determine maximal fat oxidation (MFO) and maximal aerobic power (VO_2max), and an interval cycling session during which respiratory gases were measured. The 30-min MIIT involved 5-min repetitions of workloads 20% below and 20% above the MFO intensity. VO_2max was 31.8 ± 5.5 ml·kg^-1·min^-1 and all participants achieved ≥ 3 of the designated VO_2max test criteria. The MFO identified during the GXT was not significantly different compared with the average fat oxidation rate in the MIIT session. During the MIIT session, fat oxidation rate increased with time; the highest rate (0.18 ± 0.11 g·min^{- 1}) in minute 25 was significantly higher than the rate at minute 5 and 15 (p ≤ 0.01 and 0.05 respectively). In this cohort with low aerobic fitness, fat oxidation during the MIIT session was comparable with the MFO determined during a GXT. Future research may consider if the varying workload in moderate-intensity interval training helps adherence to exercise without compromising fat oxidation.

Key Points

• Fat oxidation during interval exercise is not com-promised by the undulating exercise intensity
• Physiological measures corresponding with the MFO measured during the GXT correlated well to the MIIT
• The validity of exercise intensity markers derived from a GXT to reflect the physiological responses during MIIT.

Key Words: Interval exercise, FAT_max, maximal fat oxidation, obesity     

Higher Precision of Heart Rate Compared with VO2 to Predict Exercise Intensity in Endurance-Trained Runners

The aim of the present study was to assess the precision of oxygen uptake with heart rate regression during track running in highly-trained runners. Twelve national and international level male long-distance road runners (age 30.7 ± 5.5 yrs, height 1.71 ± 0.04 m and mass 61.2 ± 5.8 kg) with a personal best on the half marathon of 62 min 37 s ± 1 min 22 s participated in the study. Each participant performed, in an all-weather synthetic track five, six min bouts at constant velocity with each bout at an increased running velocity. The starting velocity was 3.33 m·s^-1 with a 0.56 m·s^-1 increase on each subsequent bout. VO₂ and heart rate were measured during the runs and blood lactate was assessed immediately after each run. Mean peak VO₂ and mean peak heart rate were, respectively, 76.2 ± 9.7 mL·kg^-1·min^-1 and 181 ± 13 beats·min^-1. The linearity of the regressions between heart rate, running velocity and VO₂ were all very high (r > 0.99) with small standard errors of regression (i.e. Sy.x < 5% at the velocity associated with the 2 and 4 mmol·L^-1 lactate thresholds). The strong relationships between heart rate, running velocity and VO₂ found in this study show that, in highly trained runners, it is possible to have heart rate as an accurate indicator of energy demand and of the running speed. Therefore, in this subject cohort it may be unnecessary to use VO₂ to track changes in the subjects’ running economy during training periods.

Key points

• Heart rate is used in the control of exercise intensity in endurance sports.
• However, few studies have quantified the precision of its relationship with oxygen uptake in highly trained runners.
• We evaluated twelve elite half-marathon runners during track running at various intensities and established three regressions: oxygen uptake / heart rate; heart rate / running velocity and oxygen uptake / running velocity.
• The three regressions presented, respectively, imprecision of 4,2%, 2,75% and 4,5% at the velocity associated with the 4 mmol·L^-1 threshold.
• The results of the present study show that, in highly trained runners, it is possible to use heart rate as an accurate index of the external work rate during sub maximal running speeds.

Key words: Running velocity, internal load, relationships, standard error     

Physiological Demands of Simulated Off-Road Cycling Competition

The purpose of the study was to measure the demands of off-road cycling via portable spirometry, leg-power output (PO), heart rate (HR) and blood lactate (BLa) concentration. Twenty-four male competitive cyclists (age: 29±7.2 yrs, height: 1.79 ± 0.05 m, body mass: 70.0 ± 4.9 kg, VO_2peak: 64.9 ± 7.5 ml·kg^-1·min^-1) performed simulated mountain bike competitions (COMP) and laboratory tests (LabT). From LabT, we determined maximal workload and first and second ventilatory thresholds (VT1, VT2). A high-performance athlete (HPA) was used for comparison with three groups of subjects with different sport-specific performance levels. Load profiles of COMP were also investigated during uphill, flat and downhill cycling. During the COMP, athletes achieved a mean oxygen uptake (VO_2COMP) of 57.0 ± 6.8 ml·kg^-1·min^-1 vs. 71.1 ml·kg^-1·min^-1 for the HPA. The PO_COMP was 2.66±0.43 W·kg^-1 and 3.52 W·kg^-1 for the HPA. PO_COMP, VO_2COMP and HR_COMP were compared to corresponding variables at the VT2 of LabT. LabT variables correlated with racing time (RT_COMP) and PO_COMP (p < 0.01 to <0.001; r-0.59 to -0.80). The VO_2peak (LabT) accounted for 65% of variance of a single COMP test. VO_2COMP, PO_COMP and also endurance variables measured from LabTs were found as important determinants for cross-country performance. The high average VO_2COMP indicates that a high aerobic capacity is a prerequisite for successful COMP. Findings derived from respiratory gas measures during COMPs might be useful when designing mountain bike specific training.

Key points

• Cross- country cycling is characterized by high oxygen costs due to the high muscle mass simultaneously working to fulfill the demands of this kind of sports.
• Heart rate and blood lactate concentration measures are not sensitive enough to assess the energy requirements of COMP. Therefore, respiratory gas and power output measures are helpful to provide new information to physiological profile of cross- country cycling.
• An excellent cycling-specific capacity is a prerequisite for successful off-road cycling.
• Data determined from LabT might be utilized to describe semi-specific abilities of MB- athletes on a cycle ergometer, while data originating from COMP might be useful when designing a mountain bike specific training.

Key words: Off-road cycling, mountain biking, oxygen uptake, power output, lactate, heart rate     

Heart Rate Response During Underwater Treadmill Training in Adults with Incomplete Spinal Cord Injury

Background:

Walking on a submerged treadmill can improve mobility in persons displaying lower limb muscle weakness and balance deficits. Little is known, however, regarding the effect of water treadmill exercise on cardiac performance in persons with incomplete spinal cord injury (iSCI).

Objective:

To assess heart rate response during underwater treadmill training (UTT) in adults with iSCI.

Methods:

Seven males and 4 females with iSCI (age = 48 ± 13 years; 5 ± 8 years after injury) completed 8 weeks of UTT (3 sessions per week; 3 walks per session) incorporating individually determined walking speeds, personalized levels of body weight unloading, and gradual, alternating increases in speed and duration. Heart rate was monitored during the last 15 seconds of the final 2 minutes of each walk.

Results:

Over the course of 3 biweekly periods in which walking speed remained constant, heart rate fell by 7% (7 ± 1 b•min^-1; P < .001) in weeks 2 and 3, 14% (17 ± 6 b•min^-1; P < .001) in weeks 4 and 5, and 17% (21 ± 11 b•min^-1; P < .001) in weeks 6 and 7.

Conclusion:

In adults with iSCI, progressively greater absolute and relative reductions in submaximal exercise heart rate occurred after 2 months of UTT featuring a systematic increase in training volume.     

Bioharness? Multivariable Monitoring Device: Part. I: Validity

The Bioharness^™ monitoring system may provide physiological information on human performance but there is limited information on its validity. The objective of this study was to assess the validity of all 5 Bioharness^™ variables using a laboratory based treadmill protocol. 22 healthy males participated. Heart rate (HR), Breathing Frequency (BF) and Accelerometry (ACC) precision were assessed during a discontinuous incremental (0-12 km·h^-1) treadmill protocol. Infra-red skin temperature (ST) was assessed during a 45 min^-1 sub-maximal cycle ergometer test, completed twice, with environmental temperature controlled at 20 ± 0.1 °C and 30 ± 0.1 °C. Posture (P) was assessed using a tilt table moved through 160°. Adopted precision of measurement devices were; HR: Polar T31 (Polar Electro), BF: Spirometer (Cortex Metalyser), ACC: Oxygen expenditure (Cortex Metalyser), ST: Skin thermistors (Grant Instruments), P:Goniometer (Leighton Flexometer). Strong relationships (r = .89 to .99, p < 0.01) were reported for HR, BF, ACC and P. Limits of agreement identified differences in HR (-3.05 ± 32.20 b·min^-1), BF (-3.46 ± 43.70 br·min^-1) and P (0.20 ± 2.62°). ST established a moderate relationships (-0.61 ± 1.98 °C; r = 0.76, p < 0.01). Higher velocities on the treadmill decreased the precision of measurement, especially HR and BF. Global results suggest that the BioharressTM is a valid multivariable monitoring device within the laboratory environment.

Key points

• Different levels of precision exist for each variable in the Bioharness^™ (Version 1) multi-variable monitoring device
• Accelerometry and posture variables presented the most precise data
• Data from the heart rate and breathing frequency variable decrease in precision at velocities ≥ 10 km·h^-1
• Clear understanding of the limitations of new applied monitoring technology is required before it is used by the exercise scientist

Key words: Physiological technology, precision of measurement, exercise     

Acute Effects of Three Different Circuit Weight Training Protocols on Blood Lactate,Heart Rate,and Rating of Perceived Exertion in Recreationally Active Women

Interval and circuit weight training are popular training methods for maximizing time-efficiency, and are purported to deliver greater physiological benefits faster than traditional training methods. Adding interval training into a circuit weight-training workout may further enhance the benefits of circuit weight training by placing increased demands upon the cardiovascular system. Our purpose was to compare acute effects of three circuit weight training protocols 1) traditional circuit weight training, 2) aerobic circuit weight training, and 3) combined circuit weight-interval training on blood lactate (BLA), heart rate (HR), and ratings of perceived exertion (RPE). Eleven recreationally active women completed 7 exercise sessions. Session 1 included measurements of height, weight, estimated VO₂max, and 13 repetition maximum (RM) testing of the weight exercises. Sessions 2-4 were held on non-consecutive days for familiarization with traditional circuit weight training (TRAD), aerobic circuit weight training (ACWT), and combined circuit weight-interval training (CWIT) protocols. In sessions 5-7, TRAD, ACWT, and CWIT were performed in a randomized order ≥ 72 hr apart for measures of BLA, HR, and RPE at pre-exercise and following each of three mini-circuit weight training stations. Repeated-measures ANOVAs yielded significant interactions (p < 0.05) in BLA, HR, and RPE. Combined circuit weight-interval training (CWIT) produced higher BLA (7.31 ± 0.37 vs. TRAD: 3.99 ± 0.26, ACWT: 4.54 ± 0.31 mmol.L^-1), HR (83.51 ± 1.18 vs. TRAD: 70.42 ± 1.67, ACWT: 74.13 ± 1.43 beats.min^-1) and RPE (8.14 ± 0.41 vs. TRAD: 5.06 ± 0.43, ACWT: 6.15 ± 0.42) at all measures. Aerobic circuit weight training (ACWT) elicited greater RPE than traditional circuit weight training (TRAD) at all measures. Including combined circuit weight-interval training (CWIT) workouts into exercise programming may enhance fitness benefits and maximize time-efficiency more so than traditional circuit training methods.

Key points

• Combining circuit weight training with interval training requires people to exercise at a higher intensity.
• The moderately trained can obtain fitness benefits from including interval training as part of a circuit weight training protocol.
• Merging circuit weight training with interval training may be a desirable option for those with limited time to exercise.

Key words: Interval training, repetition maximum, resistance training     

Recovery of Power Output and Heart Rate Kinetics During Repeated Bouts of Rowing Exercise with Different Rest Intervals

This study examined the effect of recovery time on the maintenance of power output and the heart rate response during repeated maximal rowing exercise. Nine male, junior rowers (age: 16 ± 1 years; body mass: 74.0 ± 9.1 kg; height: 1.78 ± 0.03 m) performed two consecutive all-out 1000 m bouts on a rowing ergometer on three separate occasions. The rest interval between the two bouts was 1.5 (INT1.5), 3 (INT3) and 6 min (INT6), allocated in random order. Power output was averaged for each 1000 m bout and for the first and last 500 m of each bout. Heart rate kinetics were determined using a two-component exponential model. Performance time and mean power output for the first bout was 209 ± 3 s and 313 ± 10 W respectively. Recovery of mean power output was incomplete even after 6 min (78 ± 2, 81 ± 2 and 84 ± 2 % for INT1.5, INT3 and INT6 respectively). Mean power output after INT6 was higher (p < 0.01) only compared with INT1.5. Power output during the first 500 m of bout 2 after INT6 was 10% higher compared with the second 500 m. During INT1.5 and INT3 power output during the first and the second 500 m of bout 2 was similar. Peak heart rate (~197 b·min^-1) and the HR time constant (~13 s) were unaffected by prior exercise and recovery time. However, when the recovery was short (INT1.5), HR during the first 50 s of bout 2 was significantly higher compared with corresponding values during bout 1. The present study has shown that in order to maintain similar power outputs during repeated maximal rowing exercise, the recovery interval must be greater than 6 min. The influence of a longer recovery time (INT6) on maintenance of power output was only evident during the first half of the second 1000 m bout.

Key Points

• The recovery of mean power output during two repeated maximal 1000 m bouts of rowing exercise was incomplete even after a 6 min rest interval.
• The benefit of the longer rest interval was apparent only during the first 500 m of bout 2.
• The HR time constant was unaffected by prior exercise and the time of recovery. However, when the recovery was short, HR during the first 50 s of bout 2 was significantly higher compared with the corresponding values of bout 1.

Key words: Interval training, maintenance of power output     

Physiological Responses and Predictors of Performance in a Simulated Competitive Ski Mountaineering Race

Competitive ski mountaineering (SKIMO) has achieved great popularity within the past years. However, knowledge about the predictors of performance and physiological response to SKIMO racing is limited. Therefore, 21 male SKIMO athletes split into two performance groups (elite: VO_2max 71.2 ± 6.8 ml· min^-1· kg^-1 vs. sub-elite: 62.5 ± 4.7 ml· min^-1· kg^-1) were tested and analysed during a vertical SKIMO race simulation (523 m elevation gain) and in a laboratory SKIMO specific ramp test. In both cases, oxygen consumption (VO₂), heart rate (HR), blood lactate and cycle characteristics were measured. During the race simulation, the elite athletes were approximately 5 min faster compared with the sub-elite (27:15 ± 1:16 min; 32:31 ± 2:13 min; p < 0.001). VO₂ was higher for elite athletes during the race simulation (p = 0.046) and in the laboratory test at ventilatory threshold 2 (p = 0.005) and at maximum VO₂ (p = 0.003). Laboratory maximum power output is displayed as treadmill speed and was higher for elite than sub-elite athletes (7.4 ± 0.3 km h^-1; 6.6 ± 0.3 km h^-1; p < 0.001). Lactate values were higher in the laboratory maximum ramp test than in the race simulation (p < 0.001). Pearson’s correlation coefficient between race time and performance parameters was highest for velocity and VO₂ related parameters during the laboratory test (r > 0.6). Elite athletes showed their superiority in the race simulation as well as during the maximum ramp test. While HR analysis revealed a similar strain to both cohorts in both tests, the superiority can be explainable by higher VO₂ and power output. To further push the performance of SKIMO athletes, the development of named factors like power output at maximum and ventilatory threshold 2 seems crucial.Key points

• VO₂ measurements in the laboratory and the field confirm the high involvement of the aerobic system in SKIMO
• Elite athletes showed their supremacy in the laboratory test and the simulated vertical race
• Relative heart rate, relative VO₂ and lactate values indicate the same emphasized strain for elite and sub-elite athletes during SKIMO vertical racing.
• Peak speed, peak lactate and VO_2max were the highest in lab predictors of outdoor SKIMO vertical race performance.

Key words: Performance diagnosis, predictors of performance, oxygen uptake, competition simulation, winter sports physiology, ski mountaineering     

Effects of Aging on Perceived Exertion and Pain During Arm Cranking in Women 70 to 80 YEARS OLD

The aim of this study was to examine the effects of aging on perceived exertion (PE) and perceived arm pain (PaP) at the end of a maximal graded arm test in 70- to 80-year -old women. Twelve healthy young (mean age 22.9 ± 3.3 years), and 12 healthy elderly (mean age 74.6 ± 3.7 years) women performed a maximal graded test (GXT) on an arm crank ergometer until exhaustion. The results revealed no significant difference between both groups concerning PE (p > 0.05; Effect Size = 0.62) and when heart rate (HR) was expressed as a theoretical maximal heart rate (THRmax) (p > 0.05; Effect Size = 0.17). Nevertheless, PaP was significantly lower (p < 0.05; Effect Size = 2.95) in the elderly compared to the young group. In conclusion, these results suggest that, at the end of GXT, PE is not influenced, whereas PaP may be altered by aging of the women tested in the present study. Therefore, it appears difficult to use PaP in these elderly women to regulate exercise intensity during a training program.

Key Points

• At the end of a maximal graded arm test, perceived exertion is not influenced, whereas perceived arm pain may be altered by aging.
• It appears difficult to use perceived arm pain in elderly women to regulate exercise intensity during a training program.

Key words: CR 10, elderly, pain, exercise     

Hemodynamic and Lactic Acid Responses to Proprioceptive Neuromuscular Facilitation Exercise

The hemodynamic and metabolic responses to proprioceptive neuromuscular facilitation (PNF) exercise were examined in 32 male university students (aged 19-28 years). Ten repetitions of PNF exercises were applied to the subjects’ dominant upper extremities in the following order: as an agonist pattern flexion, adduction and external rotation; and as an antagonist pattern extension, abduction and internal rotation. Heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), double product (DP), and blood lactate concentration (La) were determined before, immediately after, and at 1^st, 3^rd, and 5^th minutes after PNF exercise. A one-way ANOVA with repeated measures indicated significant differences in HR, SBP, DBP, DP and La immediately after PNF exercise. HR increased from 81 (±10) to 108 (±15) b·min^-1 (p < 0.01), SBP increased from 117 (±10) to 125 (±11) mmHg (p < 0.01), DBP increased from 71 (±10) to 75 (±8) mmHg (p < 0.01), DP increased from 96 (±16) to 135 (±24) (p < 0.01), and La increased from 0.69 (±0.31) to 3.99 (±14.63) mmol·L^-1 (p < 0.01). Thus PNF exercise resulted in increased hemodynamic responses and blood lactate concentration that indicate a high strain on the cardiovascular system and anaerobic metabolism in healthy subjects.

Key Points

• PNF exercises resulted in increased hemodynamic responses.
• Repeated PNF exercises resulted in an increased blood lactate concentration.

Key words: Heart rate, systolic blood pressure, diastolic blood pressure, double product, PNF     

Oxygen Uptake Kinetics in Endurance Trained Youth and Adult Cyclists

Previous studies reported faster pulmonary oxygen uptake kinetics at the onset of exercise in untrained youth compared with adults. Whether or not these differences are identical for trained groups have not been examined. The purpose of this study was to compare ˙VO₂ kinetics of youth and adult cyclists at moderate and heavy-intensity exercise. Thirteen adult (age: 23.2 ± 4.8 years; ˙VO_2peak 68.4 ± 6.8 mL·min^-1.kg^-1) and thirteen youth cyclists (age: 14.3 ± 1.5 years; ˙VO_2peak 61.7 ± 4.3 mL·min^-1.kg^-1) completed a series of 6-min square wave exercises at moderate and heavy-intensity exercise at 90 rev·min^-1. A two-way repeated-measure ANOVA was conducted to identify differences between groups and intensities. The time constant, time delay and the mean response time were not significantly different between youth and adult cyclists (p > 0.05). We found significant differences between intensities, with a faster time constant during moderate than heavy-intensity exercise in youth (24.1 ± 7.0 s vs. 31.8 ± 5.6 s; p = 0.004) and adults (22.7 ± 5.6 s vs. 28.6 ± 5.7 s; p < 0.001). The present data suggest that the effect of training history in adult cyclists compensate for the superior primary response of the oxygen uptake kinetics typically seen in youth compared to adults. Furthermore, the ˙VO₂ response is dependent of work rate intensity in trained youth and adult cyclists.Key points

• No differences in the primary response between youth and adult cyclists at moderate and heavy-intensity exercise
• This suggests that adaptations to long-term training have a high potential as an influencing factor on the response of oxygen uptake kinetics
• Oxygen uptake kinetics are influenced by work rate in both youth and adult cyclists with a slower response at higher work rates.

Key words: Adolescents, endurance training, exercise physiology, physical performance, trained athletes     

Maximal Oxygen Uptake cannot be Determined in the Incremental Phase of The Lactate Minimum Test on a Cycle Ergometer

The aim of this study was to investigate the maximal oxygen uptake (VO_2MAX) determined using the incremental phase of the lactate minimum test (LM) on a cycle ergometer. Fifteen trained men were submitted to a graded exercise test (GXT) to evaluate the VO_2MAX and LM. The total durations of the GXT and LM were 11.2±1.8 minutes (CI95%:10.2-12.3 minutes) and 25.3±3.2 minutes (CI95%:23.5-27.0), respectively. For the variables measured at exhaustion in both the GXT and LM, the oxygen uptake (54.6 ± 8.1 ml·kg⁻¹·min⁻¹vs 50.0 ± 7.7 ml·kg⁻¹·min⁻¹), carbon dioxide production (66.1 ± 7.5 ml·kg⁻¹·min⁻¹ vs 50.4 ± 8.0 ml·kg⁻¹·min⁻¹), ventilation (153.9 ± 19.0 L·min⁻¹ vs 129.9 ± 22.9 L·min⁻¹), respiratory exchange ratio (1.22 ± 0.10 vs1.01 ± 0.05), maximal power output achieved (331.6 ± 45.8 W vs 242.4 ± 41.0 W), heart rate (183.1 ± 6.9 bpm vs175.9 ± 10.6 bpm) and lactate (10.5 ± 2.3 mmol·L⁻¹ vs 6.6 ± 2.2 mmol·L⁻¹) were statistically lower in the LM (p < 0.05). However, the values of rating of perceived exertion (17.6 ± 2.5 for GXT and 17.2 ± 2.3 for LM) did not differ (ES = 0.12 and CV = 7.8%). There was no good agreement between the values of the VO_2MAX from the GXT and VO_2PEAK from the LM, as evidenced in the Bland-Altman plot (4.7 ml·kg⁻¹·min⁻¹ and 0.34 L·min⁻¹ of mean differences, respectively), as well as the high values of the upper and lower limits of agreement. We conclude that the VO_2PEAK values obtained in the incremental phase of the LM underestimate the VO_2MAX.

Key points

• The VO_2MAX is not attained during the incremental phase of the lactate minimum test;
• The physiological responses at exhaustion during LM are not similar to physiological responses measured during GXT;
• There is a weak agreement between the peak VO₂ measured at exhaustion during LM and the VO_2MAX measured during GXT.

Key words: Maximal aerobic power, aerobic capacity, aerobic and anaerobic fitness     

The Effects of Sodium Citrate Ingestion on Metabolism and 1500-m Racing Time in Trained Female Runners

The purpose of the study was to assess the effects of sodium citrate ingestion on the metabolic response to exercise and performance in a 1500-m competitive run in trained female middle-distance runners in field conditions. Seventeen athletes (mean (± SD) aged 18.6 ± 2.5 years, VO₂max 55.2 ± 7.6 ml·kg^-1·min^-1) competed in two 1500-m races following ingestion of 0.4 g·kg^-1 body mass of sodium citrate (CIT) and placebo (PLC - 1.0% solution of NaCl). The two substances, CIT and PLC were administered in 800 ml of solution in a randomly assigned double-blind crossover manner. Capillary blood samples were analysed for lactate, glucose, haemoglobin and haematocrit before administering the solutions (baseline) as well as before and after both 1500-m races. The athletes’ times for trials CIT and PLC were 321.4 ± 26.4 and 317.4 ± 22.5 s, respectively (p > 0.05). A greater relative increase in plasma volume after administering the experimental solution, an increased body mass (by 0.4 kg; p = 0.006) immediately before the race and a restrained increase in blood glucose concentration (by 2.5 ± 1.2 mmol·l^-1 vs 3.4 ± 0.8 mmol·l^-1; p = 0.002) during the race were observed in the CIT trial compared to the PLC. A significant relationship was observed between body mass of the subjects immediately before the race and performance time (r = 0.374; p = 0.029). There were no between-treatment differences in heart rate in any stage of the run or in blood lactate accumulation during the race (final concentration of lactate was 14.4 ± 3.0 mmol·l^-1 and 13.4 ± 2.5 mmol·l^-1 (p > 0.05) in the CIT and PLC trials, respectively). The results suggest that sodium citrate induces an increase in water retention before exercise and may modify carbohydrate metabolism in high intensity running, but does not improve performance in 1500-m competitive run in female middle-distance runners.

Key points

• Previous studies have found that sodium bicarbonate administration may enhance performance in male athletes in running distances of 400-1500 m.
• The use of sodium bicarbonate in competitive sports is limited because it induces gastrointestinal distress in many subjects.
• The limited data on the effects of sodium citrate ingestion on the metabolic response to exercise and performance suggest that it may have all the benefits of sodium bicarbonate without the associated negative side effects.
• We assessed the effects of sodium citrate ingestion on the metabolic response to exercise and performance in a 1500-m competitive run in trained young female middle-distance runners.
• The results suggest that sodium citrate induces an increase in water retention before exercise and may modify carbohydrate metabolism in high intensity running, but does not improve performance in 1500-m competitive run in female middle-distance runners.

Key words: Middle-distance running, buffer ingestion, ergogenic aid     

Cardiorespiratory Characteristics and Cholesterol Responses to a Single Session of Heavy Leg Press Exercise

The effect of resistance exercise on blood lipids is not clear yet. The purpose of this study was to examine the cholesterol responses to a heavy resistance leg press exercise emphasizing on the eccentric movement 24 and 48 hours following exercise and to quantify the cardiorespiratory responses of the exercise bout in an attempt to clarify the exercise characteristics that may be responsible for the effects of heavy resistance exercise on blood lipids. Nine healthy, untrained male volunteers aged 27.2 ± 1.1 yrs (76.2 ± 2.5 kg, 1.79 ± 0.02 m) performed a session of heavy RE emphasizing on the eccentric movement consisting of eight sets of inclined leg presses at six repetition maximum with 3-min rest intervals. Venous blood samples were obtained at rest (control) and 24 and 48 hours following exercise. Average VO₂ at rest was 4.0 ± 0.4 ml·min⁻¹·kg⁻¹, during exercise 19.6 ± 0.2 ml·min⁻¹·kg⁻¹ and during the 180 sec recovery period between sets 12.5 ± 0.2 ml·min⁻¹·kg⁻¹. RER values decreased with the progression of the exercise and were significantly lower during the last four sets compared with the first four sets of the exercise session. Resting heart rate was 67 ± 2 bpm, and maximum heart rate during exercise was 168 ± 1 bpm. Serum creatine kinase was significantly elevated on day 1 (1090 ± 272 U·L⁻¹, p < 0.03) and peaked on day 2 (1230 ± 440 U·L⁻¹ p < 0. 01). Total cholesterol, HDL cholesterol and calculated LDL cholesterol concentration did not change significantly following with exercise. This protocol of heavy resistance exercise has no effect on TC or cholesterol sub-fraction concentration 24 and 48 hours following exercise which may be due to the low energy expenditure of the exercise and/or to the gender of the participants.

Key points

• Repeated sets of heavy resistance exercise significantly increase oxygen uptake both during exercise and the following recovery period.
• Even though exercise was of low volume (8 sets x 6 repetitions) the elevated oxygen uptake during the rest intervals in combination with the total exercise session duration (26 min) resulted in aerobic energy expenditure that is equivalent to low to moderate intensity cycling.
• Leg press resistance exercise emphasizing on the eccentric movement that caused muscle damage had no effect on total cholesterol, HDL-C and LDL-C during the two days following exercise in young healthy male subjects.

Key words: Muscle damage, energy expenditure, total cholesterol, HDL, oxygen uptake.     

The Occurrence of Core Muscle Fatigue During High-Intensity Running Exercise and its Limitation to Performance: The Role of Respiratory Work

This study investigated the occurrence of core muscle fatigue during high-intensity running exercise and its limitation to exercise performance. A secondary aim was to investigate whether respiratory muscle work performed during intense running periods, would contribute to core muscle fatigue. Nine male recreational runners were recruited for two reasons; (1) to perform a continuous treadmill run at 85% VO₂max with and without core muscle fatigue in the CR_F and CR trials, respectively; and (2) to mimic the treadmill run-induced respiratory response recorded in the CR trial while subjects were free of whole-body exercise (Mimic trial). The changes in global core muscle function with fatigue in this study were evaluated by performing a sport-specific endurance plank test (SEPT), and the associated influence on running performance was examined by comparing the time to exhaustion during the treadmill run between the CR and CR_F trials. Subsequent to the treadmill run in the CR trial, SEPT (255.7 ± 85.3 vs 177.3 ± 80.6 s) was reduced from baseline in all runners. The reduction correlated (r = 0.67) with the concomitant decline in inspiratory muscle function revealed by maximal inspiratory mouth pressure (PI_max: 151.3 ± 18.2 vs 133.3 ± 17.2 cmH₂O, p < 0.05). In the Mimic trial, similar results in SEPT (212.3 ± 90.2 s), PI_max (129.0 ± 26.7 cmH₂O), and correlation (r = 0.77, p < 0.05) were observed following voluntary hyperpneic activity. With the preceded fatigued core muscle workout in the CR_F trial, the running capacity was impaired significantly (10.7 ± 4.5 vs 6.5 ± 2.0 min, p < 0.05). The impairment was correlated (r=0.72) to the SEPT reduction resulting from the workout. The results suggest that a high-intensity maximum run may induce core muscle fatigue in runners. The core muscle fatigue, which may be partly attributed to the corresponding respiratory work, may limit their running endurance. Inspiratory muscle function appears to be essential for core stabilization during the intense running.

Key points

• A high-intensity maximum run may induce core muscle fatigue in runners. The core muscle fatigue, which may be partly attributed to the corresponding respiratory work, may limit their running endurance.
• In support of previous notion, inspiratory muscles may share the work of core stabilization during intense exercise, while simultaneously increasing the demand for breathing.
• Inspiratory muscle training incorporated into a running specific-core training regime potentially enhances the training effect on the core muscles in a functional manner to deal with the challenges faced during intense exercise.

Key words: Core stability, muscle function, respiratory muscle, plank test     

Indirect Calorimetry During Ultradistance Running: A Case Report

The purpose was to determine the energy expenditure during ultradistance trail running. A portable metabolic unit was carried by a male subject for the first 64.5 km portion of the Western States 100 running race. Calibrations were done with known gases and volumes at ambient temperature, humidity and pressure (23-40.5 °C and 16-40% respectively). Altitude averaged 1692.8 ± 210 m during data collection. The male subject (36 yrs, 75 kg, VO₂max of 67.0 ml·kg^-1·min^-1) had an average (mean ± SD) heart rate of 132 ± 9 bpm, oxygen consumption of 34.0 ± 6.8 ml·kg^-1·min^-1, RER of 0.91 ± 0.04, and V_E of 86.0 ± 14.3 L·min^-1 during the 21.7 km measuring period. This represented an average of 51% VO₂max and 75% heart rate maximum. Energy expenditure was 12.6 ± 2.5 kcals·min^-1, or 82.7 ± 16.6 kcals·km^-1 (134 ± 27 kcals·mile^-1) at 68.3 ± 12.5% carbohydrate. Extrapolation of this data would result in an energy expenditure of >13,000 kcals for the 160 km race, and an exogenous carbohydrate requirement of >250 kcal·hr^-1. The energy cost of running for this subject on separate, noncompetitive occasions ranged from 64.9 ± 8.5 to 74.4 ± 5.5 kcals·km^-1 (105 ± 14 to 120 ± 9 kcals·mile^-1). Ultradistance trail running increases energy expenditure above that of running on nonundulating terrain, which may result in underestimating energy requirements during these events and subsequent undernourishment and suboptimal performance.

Key Points

• The energy cost of running is elevated during ultradistance trail races compared to normal running conditions.
• This elevated energy cost results in a ~12% increase in energy expenditure for a given distance.
• Ad libitum energy intake may grossly underestimate the demand of ultradistance running in the conditions investigated in this paper, thus jeopardizing race performance.

Key words: Energy expenditure, caloric expenditure, running economy     

Short Duration Heat Acclimation in Australian Football Players

This study examined if five sessions of short duration (27 min), high intensity, interval training (HIIT) in the heat over a nine day period would induce heat acclimation in Australian football (AF) players. Fourteen professional AF players were matched for VO₂peak (mL·kg^-1·min^-1) and randomly allocated into either a heat acclimation (Acc) (n = 7) or Control (Con) group (n = 7). The Acc completed five cycle ergometer HIIT sessions within a nine day period on a cycle ergometer in the heat (38.7 ± 0.5 °C; 34.4 ± 1.3 % RH), whereas Con trained in thermo-neutral conditions (22.3 ± 0.2 °C; 35.8 ± 0. % RH). Four days prior and two days post HIIT participants undertook a 30 min constant load cycling test at 60% V̇O₂peak in the heat (37.9 ± 0.1 °C; 28.5 ± 0.7 % RH) during which VO₂, blood lactate concentration ([Lac^-]), heart rate (HR), rating of perceived exertion (RPE), thermal comfort, core and skin temperatures were measured. Heat acclimation resulted in reduced RPE, thermal comfort and [Lac^-] (all p < 0.05) during the submaximal exercise test in the heat. Heart rate was lower (p = 0.007) after HIIT, in both groups. Heat acclimation did not influence any other measured variables. In conclusion, five short duration HIIT sessions in hot dry conditions induced limited heat acclimation responses in AF players during the in-season competition phase. In practice, the heat acclimation protocol can be implemented in a professional team environment; however the physiological adaptations resulting from such a protocol were limited.

Key points

• Some minor heat acclimation adaptations can be induced in professional AF players with five 27 min non-consecutive, short duration HIIT sessions in the heat.
• The heat acclimation protocol employed in this study was able to be implemented in a professional team sport environment during an actual competitive season.
• Elevating and maintaining a high core temperature sufficient for heat acclimation likely requires a longer heat training session or some pre-heating prior to exercise.

Key words: Core temperature, thermoregulation, high intensity interval training, adaptation, metabolism