Influence of training status and exercise modality on pulmonary O2 uptake kinetics in pre-pubertal girls

The limited available evidence suggests that endurance training does not influence the pulmonary oxygen uptake (V(O)(2)) kinetics of pre-pubertal children. We hypothesised that, in young trained swimmers, training status-related adaptations in the V(O)(2) and heart rate (HR) kinetics would be more evident during upper body (arm cranking) than during leg cycling exercise. Eight swim-trained (T; 11.4 +/- 0.7 years) and eight untrained (UT; 11.5 +/- 0.6 years) girls completed repeated bouts of constant work rate cycling and upper body exercise at 40% of the difference between the gas exchange threshold and peak V(O)(2). The phase II V(O)(2) time constant was significantly shorter in the trained girls during upper body exercise (T: 25 +/- 3 vs. UT: 37 +/- 6 s; P < 0.01), but no training status effect was evident in the cycle response (T: 25 +/- 5 vs. UT: 25 +/- 7 s). The V(O)(2) slow component amplitude was not affected by training status or exercise modality. The time constant of the HR response was significantly faster in trained girls during both cycle (T: 31 +/- 11 vs. UT: 47 +/- 9 s; P < 0.01) and upper body (T: 33 +/- 8 vs. UT: 43 +/- 4 s; P < 0.01) exercise. The time constants of the phase II V(O)(2)and HR response were not correlated regardless of training status or exercise modality. This study demonstrates for the first time that swim-training status influences upper body V(O)(2) kinetics in pre-pubertal children, but that cycle ergometry responses are insensitive to such differences

Transient oxygen uptake response as an indicator of sports specific adaptation

A cross-sectional design examined aerobic power and transient oxygen uptake responses of four male sports groups (cyclists, runners, swimmers, and cross-country skiers). Data was collected via three modes of ergometry (treadmill running, cycling, and arm cranking), with the transient oxygen uptake responses being described via the 'half-time' (t1/2 VO[subscript 2]on) and 'Mean Response Time' (MRT) values. The transient VO[subscript 2]on responses were quantified via a single exponential process given as [see document for formula] where A reflects the increment above the previous (rest or exercise) steady state level, ss represents the steady State or asymptotic value, TD is the time delay parameter, and T is the time constant..

Physiology of exercise in health and disease, with special reference to effort intolerance, training and thermoregulation in man

1. Davies, C.T.M., (1968) Limitdtions to the prediction of maximum oxygen intake from cardiac frequency measurements. J. Appl. Physiol. 24, 700 -706 || 2. Cotes, J.E., Davies, C.T.M., Edholm, G G., Healy, M.J.R., and Tanner, J.M., (1969). Factors relating to the aerobic capacity of 46 healthy British males and females, ages 18 -28 years. Proc. Roy. Soc. Lond. B 174, 91 -114 || 3. Davies, C.T.M., Tuxworth, W., and Young, J.M., (1970). Physiological effects of repeated exercise. Clin. Sci. 39, 247 -258 || 4. Di Prampero, P.E., Davies, C.T.M., Cerretelli, P., and Margaria R., (1970) An analysis of 02 debt contracted in submaximal exercise. J. Appl. Physiol. 29, 547 -551 || 5. Godfrey, S., and Davies, C.T.M., (1970) Estimates of arterial PCO2 and their effect on the calculated values of cardiac output and deadspace in exercise tests. Clin. Sci. 39, 529 -537 || 6. Davies, C.T.M., Kitchin, A.H., Knibbs, A.V., and Neilson, J.M., (1971) Computer Quantitation of ST segment response to graded exercise in untrained and trained normal subjects. Cardiovascular Research, 5, 201 -209 || 7. Godfrey, S., Davies, C.T.M., Wozniak, E., and Barnes, Carolyn A., (1971) Cardio -respiratory response to exercise in normal children. Clin. Sci. 40, 419 -431 || 8. Davies, C.T.M., (1972). The oxygen transporting system in relation to age. Clin. Sci. 42, 1 -13 || 9. Davies, C.T.M., Di Prampero, P.E., and Ceretelli, P., (1972) Kinetics of cardiac output and respiratory gas exchange during exercise and recovery. J. Appl. Physiol. 32, 618 -625 || 10. Edwards, R.H.T., Denison, D.M., Jones, G., Davies, C.T.M., and Campbell, E.J.M., (1972) Changes in mixed venous gas tensions at the start of exercise in man. J. Appl. Physiol. 32, 165 -169 || 11. Davies, C.T.M., and Barnes, Carolyn A., (1972) Plasma FFA in relation to maximum power output in man. Int. Z. Angew Physiol. 30, 247-257 || 12. Davies, C.T.M., Barnes Carolyn A., Fox, R.H., Ojikutu, R., Ola and Samueloff A.S., (1972). Ethnic difference in physical work capacity. J. Appl. Physiol. 33, 726 -732 || 13. Davies, C.T.M., (1973) Relationship of maximum aerobic power output to productivity and absenteeism of East African sugar cane workers. Brit. J. Ind. Med. 30, 146 -154 || 14. Davies, C.T.M., Chukweumeka, A.C., and Van Haaren, J.P.M., (1973) Iron deficiency anaemia: its effect on maximum aerobic power and responses to exercise in African males, aged 17 -40 years. Clin. Sci. 44, 555 -566 || 15. Cotes, J.E., Berry, G., Burkinshaw, L., Davies, C.T.M., Hall, A.M., Jones, P.R.M., and Knibbs, A.V., (1973). Cardiac frequency during submaximal exercise in young adults: relation to lean body mass, total body potassium and amount of leg muscle. Q.J.Expl.Physiol. 58, 239 -250 || 16. Davies, C.T.M., and Van Haaren, J.P.M., (1973) The effect of treatment the physiological responses to exercise in East African Industrial workers with iron deficiency anaemia. Brit. J. Ind. Med. 30, 335 -340. || 17. Sargeant, A.J., and Davies, C.T.M., (1973). Perceived exertion during rhythmic exercise involving different muscle masses. Human Ergology, 2, 3 -11 || 18. Davies, C.T.M., Sargeant, A.J., and Smith, B., (1974). The physiological responses to running downhill. Europ. J. Appl. Physiol. 32, 187 -194 || 19. Davies, C.T.M., and Sargeant, A.J., (1974) Physiological responses to standardised arm work. Ergonomics 17, 41 -49 || 20. Davies, C.T.M., and Sargeant, A.J., (1974). Exercise performance with one and two -legs breathing air and 45% oxygen. J. Appl. Physiol. 36, 142 -148 || 21. Davies, C.T.M., Few J.D., Foster, K.G., and Sargeant, A.J., (1974). Plasma catecholamine concentration during dynamic exercise involving different muscle groups. Eur. J. Appl. Physiol. 32, 195 -206 || 22. Davies, C.T.M., and Sargeant, A.J., (1974). Indirect determination of maximal aerobic power during work with one or two limbs. Europ. J. Appl. Physiol. 32, 207 -215 || 23. Davies, C.T.M., and Sargeant, A.J., (1974). Effects of hypoxic training on normoxic maximal aerobic power output. Europ. J. Appl. Physiol. 33, 227 -236 || 24. Davies, C.T.M., and Sargeant, A.J., (1975) Changes in physiological performance of the lower limb after fracture and subsequent rehabilitation Clin. Sci. & Mol. Med. 48, 107 -114 || 25. Davies, C.T.M., and Sargeant, A.J., (1975) physiological responses to 1 and 2 leg 377 -381 || 26. Davies, C.T.M., and Sargeant, A.J., (1975). exercise in patients following fracture J. Rehab. Med. 7, 45 -50. Effects of training on the work. J. Appl. Physiol. 38, Physiological responses to of the lower limb. Scand. || 27. Davies, C.T.M., Godfrey, S., Light, M., Sargeant, A.J., and Zeidifard, E.,. (1975) Cardiopulmonary responses to exercise in obese girls and young women. J. Appl. Physiol. 38, 373 -376 || 28. Davies, C.T.M., and Sargeant, A.J., (1975) Circadian variation in physiological responses to exercise on a stationary bicycle ergometer Brit. J. Ind. Med. 32, 110 -114 || 29. Collins, K.J. Brotherhood, J.R., Davies, C.T.M., Dore, Caroline, Hackett, J., Imms, F.J., Musgrove, J., Weiner, J.S., Amin, M.A., El Karim, M., Ismail, H11.M., Omer A.J.S., and Sukkar, M.Y., (1976). Physiological performance and work capacity of Sudanese can cutters with Schistosoma mansoni infection. Amer. J. Trop. Med. & Hyg. 25, 401,421 || 30. Nielsen, B., and Davies, C.T.M., (1976). Temperature regulation during exercise in water and air. Acta Physiol. Scand. 98, 500 -508 || 31. Davies, C.T.M., Brotherhood, J.R., Few,J.D., and Zeidifard, E., (1976) Effects of ß blockade and atropinisation on plasma catecholamine concentration during exercise. Eur. J. Appl. Physiol. 36, 49 -56 || 32. Davies, C.T.M., Brotherhood, J.R., and Zeidifard, E., (1976). Temperature regulation during severe exercise with some observations on the effects of skin wetting. J. Appl. Physiol. 41, 772 -776 || 33. Sargeant, A.J., Davies, C.T.M., Edwards, R.H.T., Maunder, C., and Young A., (1977). Functional and structural changes after disuse of human muscle. Clin. Sci. & Mol. Med. 52,337 -342 || 34. Sargeant, A.J., and Davies, C.T.M., (1977). Forces applied to cranks of a bicycle ergometer during one and two leg cycling. J. Appl. Physiol. 42, 514 -518 || 35. Sargeant, A.J., & Davies, C.T.M., (1977). The effect of disuse muscular atrophy on the forces generated in dynamic exercise. Clin. Sci. & Mol. Med. 53, 182 -188 || 36. Fohlin, L., Freyschuss, E., Bjarke, B., Davies, C.T.M., and Thoren, C., (1978). Function and Dimensions of the circulatory system in anorexia nervosa. Acta. Paed. Scand. 67, 11 -16 || 37. Davies, C.T.M., Von Dobeln, W. Fohlin, L., Freyschuss u., and Thoren, C., (1978). Total body potassium, fat free weight and maximal aerobic power in children with Anorexia Nervosa. Acta. Pediatr. Scand. 67, 229 -334 || 38. Davies, C.T.M., Brotherhood, J.P., and ZeidiFard, E., (1978). Effects of Atropine and (3-Blockade on Temperature Regulation and Performance during Prolonged Exercise. Europ. J. Appl. Physiol. 38, 225 -232 || 39. Zeidifard, E., and Davies, C.T.M., (1978). An Assessment of a N20 Rebreathing Method for the Estimation of Cardiac Output During Severe Exercise. Ergonomics, 21, 567 -572 || 40. Sargeant,A.J., Crawley, M.A., and Davies, C.T.M., (1979). Physiological Responses to Exercise in Myocardial Infarction Patients Following Residential Rehabilitation. Arch. Phys. Med. Rehabil. 60, 121 -125 || 41. Davies, C.T.M., (1979). The effects of different levels of heat production induced by diathermy and eccentric work on thermoregulation during exercise at a given skin temperature. Eur. J. Appl. Physiol. 40, 171 -180 || 42. Davies, C.T.M., and Thompson, M.W., (1979). Aerobic Performance of Female Marathon and Male Ultra- marathon Athletes. Eur. J. Appl. Physiol. 41, 233 -245 || 43. Davies, C.T.M., (1979). Thermoregulation during exercise in relation to sex and age. Eur. J. Appl. Physiol. 42, 71 -79 || 44. Davies, C.T.M., (1979). Influence of skin temperature on sweating and aerobic performance during severe work. J. Appl. Physiol. 47, 770 -777 || 45. Davies, C.T.M., and Sargeant, A.J., (1979). The effects of atropine and Practolol on the perception of exertion during treadmill exercise. Ergonomics 22, 1141 -1146 || 46. C.T.M., Fohlen L., and Temperature regulation in Anorexia nervosa patients during prolonged exercise. Acta. Med. Scand. 205, 257 -262 || 47. Davies, C.T.M., (1980) Influence of air flow and skin temperature on sweating during and following exercise. Ergonomics. 23, 559 -569 || 48. Davies, C.T.M., Fohlen L., and Thoren C., (1979) The effects of wind resistance on the forward motion of a runner. J. Appl. Physiol. 48, 702 -709 || 49. Davies, C.T.M., (1980) Metabolic cost of exercise and physical performance in children with some observations on external loading. Eur. J. Appl. 45, 95 -102 || 50. Davies, C.T.M., (1980) Effect of air resistance on the metabolic cost and performance of cycling. Eur. J. Appl. Physiol. 45, 245 -254

Aerobic Fitness and Trainability in Healthy Youth: Gaps in Our Knowledge

Peak oxygen uptake (V̇O2) is widely recognized as the criterion measure of young people’s aerobic fitness. Peak V̇O2 in youth has been assessed and documented for over 75 years but the interpretation of peak V̇O2 and its trainability are still shrouded in controversy. Causal mechanisms and their modulation by chronological age, biological maturation and sex remain to be resolved. Furthermore, exercise of the intensity and duration required to determine peak V̇O2 is rarely experienced by most children and adolescents. In sport and in everyday life young people are characterized by intermittent bouts of exercise and rapid changes in exercise intensity. In this context it is the transient kinetics of pulmonary V̇O2 (pV̇O2), not peak V̇O2, which best describe aerobic fitness. There are few rigorously determined and appropriately analyzed data from young people’s pV̇O2 kinetics responses to step changes in exercise intensity. Understanding of the trainability of pV̇O2 kinetics is principally founded on comparative studies of trained and untrained youth and much remains to be elucidated. This paper reviews peak V̇O2, pV̇O2 kinetics, and their trainability in youth. It summarizes “what we know,” identifies significant gaps in our knowledge, raises relevant questions, and indicates avenues for future research

Characterisation of cardiorespiratory responses to electrically stimulated cycle training in paraplegia

Functional, electrically stimulated (FES) cycle training can improve the cardiorespiratory fitness of spinal cord injured (SCI) individuals, but the extent to which this can occur following high volume FES cycle endurance training is not known. The effect of training on aerobic endurance capacity, as determined by the appearance of respiratory gas exchange thresholds, is also unknown. The oxygen cost (O2 cost) of this type of exercise is about 3.5 times higher than that of volitional cycling, but the source of this inefficiency, and of the variation between subjects, has not yet been investigated. The electrical cost of FES cycling, measured as the stimulation charge required per Watt of power produced (stim/Pt), has neither been calculated nor investigated before. It is also not known whether a period of FES cycling can alter the O2 cost or the stim/Pt of this unique form of exercise. Additionally, the acute metabolic responses to prolonged, high intensity FES cycling after a 12-month period of high-volume training have not yet been characterised for this subject group. Accordingly, these parameters were investigated over the course of a 12-month homebased FES cycle training programme (up to 5 x 60 min per week) in 9 male and 2 female individuals with paraplegia. Outcomes were investigated using a novel, sensitive test bed that accounted for both internal and external power production (Pt). The test protocol permitted high resolution analyses of cycling power and metabolic thresholds, and a sensitive training dose-response analysis, to be performed for the first time in FES cycling. Efficiency estimates were calculated within a new theoretical framework that was developed for those with severe disability, and the stim/Pt was determined using a novel measure designed for this study. The current training programme resulted in significant improvements in cardiorespiratory fitness and peak cycling power, but only over the first 6 months when training was progressive. These improvements were positively related to the number of training hours completed during this time. It is not known whether the plateau in training response that was found after this time was due to a physiological limitation within the muscles, or to limitations in the current stimulation strategy and of the training protocol used. The efficiency of FES cycling was not significantly altered by any period of training. However, the stim/Pt of cycling had reduced over the first 6 months, probably as a result of a fibre hypertrophy within the stimulated motor units. The relationship that was found between variables after this time suggest that differences in the efficiency of FES cycling ii between subjects and over time related primarily to the stim/Pt, which determined the number of motor units recruited per unit of power produced, rather than to metabolic changes within the muscle itself. The aerobic gas exchange threshold (GET) was detected at an oxygen uptake (˙VO2) equivalent to that normally elicited by very gentle volitional exercise, even after training. This provided metabolic evidence of anaerobic fibre recruitment from the outset, as a consequence of the non-physiological motor unit recruitment pattern normally found during FES. The cardiorespiratory stress of training was found to be significantly higher than that elicited by the incremental work rate tests, calling into question the validity of using traditional, continuous incremental work rate tests for establishing the peak oxygen uptake (˙VO2peak) of FES cycling. The respiratory exchange dynamics observed over a 60 min training session were characterised and provide a unique insight into the remarkable aerobic and anaerobic capacity of trained paralytic muscles. For this particular highly motivated subject group, training for 60 min per day on more than 4 days of the week was demonstrated to be feasible, but not able to be sustained. Further work is therefore recommended to develop and to evaluate different stimulation patterns and parameters, loading strategies and training protocols. The aim would be to determine the optimal combination of training parameters that would maximise favourable training responses within a more viable and sustainable lower volume, training programme for this subject group. In conclusion, the outcomes of this multi-centre study have demonstrated the clinical significance of using otherwise redundant, paralytic leg muscles to perform functional, regular physical exercise to improve cardiorespiratory and musculoskeletal health after SCI. Additionally, the significant increases in cycling power and endurance that were achieved opened up new mobility and recreational possibilities for this group of individuals. These findings highlight the clinical and social relevance of regular FES cycle training, and the importance of integrating FES cycling into the lives of those affected by SCI. The early and judicious implementation of this form of exercise is strongly recommended for the maintenance of a healthy body, wellbeing, and of an active lifestyle after SCI

The Influence of Protocol on the Assessment of Economy of Movement

It is suggested that only data below gas exchange threshold (GET) should be used in regressions to calculate economy of movement. The purpose of this study was to compare the accuracy of the prediction from sub-GET only data (incrementalsub) and the sub & supra GET data (incrementalfull) with a fixed work rate (WR) at an intensity typical of endurance performance. Twelve physically active male participants volunteered of age 29 ± 9 years, height 1.81 ± 0.07 m and body mass 81.4 ± 10 kg. The participants completed four separate tests each on a separate day. Initially performing a maximal ramp test (20 W.min-1) to volitional exhaustion at approximately 12 min. The other three tests included an incrementalsub and incrementalfull and a fixed WR and were counterbalanced for potential order and carryover effects. All tests were carried out on an electronically braked cycle ergometer and the cadence maintained at approximately of 80 rev.min-1. The data from the maximal test was used to determine peak power, the highest V̇O² over a 15 s sequential period (V̇O²peak) and GET. The incrementalsub method consisted of five stages six min in duration with equal transitions from 50 W to 95% GET. The incrementalfull method consisted of five stages six min in duration with equal transitions from 50 W to 85% Δ. The data collection period was set at 4-6 min for these tests. The criterion fixed WR consisted of ten min duration at a WR of 75% Δ and had two data collection periods set at 4-6 and 8-10 min. The data collection period of 8-10 min was used in all further analysis; as at the 4-6 min data collection period steady state had not been attained. A linear regression was conducted on the mean oxygen uptake (V̇O²) kinetic response at each data collection stage of the five WRs in the two predictive tests and the calculation of V̇O² requirement at 75% Δ performed. These two calculated and the measured V̇O² values of economy of movement at 75% Δ were then entered into repeated measures ANOVA to identify differences in the oxygen uptake (L.min-1). The ANOVA showed a significant effect of the method on V̇O² at 75% ∆ (p < 0.001). Post hoc analysis showed that both the incrementalsub and the incrementalfull underestimated the V̇O² requirement in the fixed WR (2.90 ± 0.40 L.min-1 (p<0.001) and 3.21 ± 0.47 L.min-1 (p=0.012) vs. 3.43 ± 0.45 L.min-1). Furthermore, the incrementalsub was significantly lower than the V̇O² estimated from the incrementalfull (p=0.037). Economy of movement should not be estimated using sub-GET data points only as this significantly underestimated the measured V̇O² requirement. The use of regressions from incremental tests that use a full range of WR data will reduce this error but still underestimate the measured V̇O² requirement. The impact of incremental designs on V̇O² kinetics requires further investigation to fully understand this effect

A detailed comparison of oxygen uptake kinetics at a range of exercise intensities

It is believed that exercise performed in the heavy intensity exercise (above Gas Exchange Threshold (GXT)) domain will reach a steady state (albeit delayed). However reported modelled time constants for the slow component indicate the V̇O² response would not be complete within the duration of the exercise performed. This raises important questions regarding the concept of heavy intensity exercise and the suitability of current exponential models to describe the slow component of V̇O². .The purpose of this study was; to comprehensively describe the relationship between exercise intensity and the slow component of V̇O², and to investigate whether a steady-state in V̇O² was achieved during constant work-rates above the gas exchange threshold (GXT). Eight recreationally active male participants volunteered for this study (age: 24±8 y; Stature: 1.78±0.09 m; mass: 76.5±10.1 kg; V̇O²peak: 3.89±0.72 L.min-1). The participants were required to visit the laboratory on nine occasions for testing. The first visit involved determination of GXT and V̇O²peak with a progressive ramp exercise test. The following tests involved multiple laboratory visits, with the participants performing a square wave transition from rest to one of eight exercise intensities; -20%Δ (minus 20% of the difference in V̇O² between that at GXT and VO2peak), -10%Δ, GXT, 10%Δ, 20%Δ, 30%Δ, 40%Δ and 50%Δ. The V̇O² response was modelled using both mono and bi exponential non-linear regression techniques. Difference in the SEE for the mono and bi exponential models were analysed using a paired samples t-test, and the slope of V̇O² vs Time (for the final minute of exercise) was analysed using a one-sample t-test. A slow component of V̇O² was found for all exercise intensities. The SEE’s were significantly lower in the bi vs. mono exponential model across all exercise intensities (p<0.05). The slope was not different from 0 (p<0.05) for the final minute of any exercise intensity, indicating that a steady-state was achieved. The modelled slow component time constants are typical of literature reported values, but would indicate that V̇O² would not be achieved during the duration of the exercise. These findings demonstrate that V̇O² was in steady-state for all exercise intensities for the final minute of exercise. These findings also demonstrate that using a bi exponential model, a slow component can be modelled even below GXT and that the time constant of the slow component would be too long to result a steady-state