Sprint performance and propulsion asymmetries on an ergometer in trained high- and low-point wheelchair rugby players.

The purpose of this study was to examine the propulsion asymmetries of wheelchair athletes while sprinting on an instrumented, dual-roller ergometer system. Eighteen experienced wheelchair rugby players (8 low point (LP) (class ≤1.5) and 10 high point (HP) (class ≥2.0)) performed a 15-second sprint in their sports wheelchair on the instrumented ergometer. Asymmetry was defined as the difference in distance and power output (PO) between left and right sides when the best side reached 28 m. Propulsion techniques were quantified based on torque and velocity data. HP players covered an average 3 m further than the LP players (P = .002) and achieved faster sprint times than LP players (6.95 ± 0.89 vs 8.03 ± 0.68 seconds, P = .005) and at the time the best player finished (5.96 seconds). Higher peak POs (667 ± 108 vs 357 ± 78 W, P = .0001) and greater peak speeds that were also evident were for HP players (4.80 ± 0.71 vs 4.09 ± 0.45 m/s, P = .011). Greater asymmetries were found in HP players for distance (1.86 ± 1.43 vs 0.70 ± 0.65 m, P = .016), absolute peak PO (P = .049), and speed (0.35 ± 0.25 vs 0.11 ± 0.10 m/s, P = .009). Although HP players had faster sprint times over 28 m (achieved by a higher PO), high standard deviations show the heterogeneity within the two groups (eg, some LP players were better than HP players). Quantification of asymmetries is important not only for classifiers but also for sports practitioners wishing to improve performance as they could be addressed through training and/or wheelchair configuration.

Hot water immersion induces an acute cytokine response in cervical spinal cord injury.

PURPOSE: The dysfunctional sympathetic nervous system in individuals with cervical spinal cord injury (CSCI) impairs adrenergic responses and may, therefore, contribute to the blunted post-exercise cytokine response. The purpose of this study was to investigate an alternative way to exercise to induce an acute cytokine response by passive core temperature elevation in CSCI. METHODS: Seven male participants with a motor complete CSCI and 8 male able-bodied controls were immersed for 60 min in water set at a temperature 2 °C above the individuals' resting oesophageal temperature. Blood was collected pre, post, and every hour up to 4 h post-immersion. RESULTS: Hot water immersion resulted in an IL-6 plasma concentration mean increase of 133 ± 144 % in both groups (P = 0.001). On a group level, IL-6 plasma concentrations were 68 ± 38 % higher in CSCI (P = 0.06). In both groups, IL-8 increased by 14 ± 11 % (P = 0.02) and IL-1ra by 18 ± 17 % (P = 0.05). Catecholamine plasma concentrations were significantly reduced in CSCI (P < 0.05) and did not increase following immersion. CONCLUSIONS: Passive elevation of core temperature acutely elevates IL-6, IL-8 and IL-1ra in CSCI despite a blunted adrenergic response, which is in contrast to earlier exercise interventions in CSCI. The present study lays the foundation for future studies to explore water immersion as an alternative to exercise to induce an acute cytokine response in CSCI.

Blood lactate and ventilatory thresholds in wheelchair athletes with tetraplegia and paraplegia.

PURPOSE: The purpose of this study was to analyse the influence of spinal cord injury level on blood lactate (BLa) and ventilatory thresholds. METHODS: Ten athletes with tetraplegia (TETRA) and nine athletes with paraplegia (PARA) performed a graded wheelchair propulsion treadmill exercise step test to exhaustion. The aerobic and anaerobic BLa thresholds, the ventilatory threshold and the respiratory compensation point (RCP) were determined. RESULTS: The BLa thresholds were determined in 34 of 38 cases, ventilatory thresholds and RCPs in 31 of 38 cases. The anaerobic BLa threshold (76 ± 7 % [Formula: see text]) and the RCP (77 ± 8 % [Formula: see text]) did not differ significantly from each other (P = 0.92), with a coefficient of variation of 4.8 ± 3.4 % between thresholds. All other thresholds differed significantly from each other (P < 0.05). Thresholds expressed as the percentage of peak oxygen uptake did not differ between TETRA and PARA (P > 0.05) despite altered breathing in TETRA, which included a higher ventilatory equivalent for oxygen and a lower tidal volume. CONCLUSION: Measuring BLa leads to a higher threshold determination rate compared with ventilatory data and the anaerobic BLa threshold can be used to predict the RCP. The altered breathing in TETRA does not seem to have a pronounced effect on the ventilatory threshold or the RCP.

Spinal cord injury: known and possible influences on the immune response to exercise.

A spinal cord injury (SCI) can increase the risk of infection by impacting on many aspects of immune function; one particularly well-documented observation is a reduction in lymphocyte numbers. The vast majority of lymphoid cells express adrenergic receptors. Therefore, autonomic function loss and concomitant alterations in resting and post-exercise catecholamine concentrations, particularly so in individuals with a tetraplegia, may impact directly on immune cells and depress immunity. Other factors are further likely to contribute, examples including altered muscular, endocrine and cardiovascular function following SCI. However, some alterations, such as increases in natural killer cell cytotoxicity following exercise in those with a tetraplegia, are unrelated to the catecholamine response. Likewise, mucosal immunity in individuals with a tetraplegia appears to be similarly influenced by exercise as in the able-bodied population. Indeed, rehabilitation therapy and exercise can increase some measures of immunity and autonomic function in those with an SCI. It is therefore possible that compensatory mechanisms offset disability-related detriments. This may be by way of sympathetic reflex activity, receptor hypersensitivity, or parasympathetic and neuroendocrine adjustments. Future work needs to explore these mechanisms further to clarify the implications of an SCI on the immune response to exercise and susceptibility to infection. In this article, we review the impacts of an SCI on immune, and specifically, exercise immune function. The relevant anatomical and physiological foundations of the immune system are first briefly laid out in order to understand the potential impacts of neural and neuroendocrine dysfunction on the immune system. With the limited number of human studies available, we have then aimed specifically to gather all relevant existing literature on exercise immunology in individuals with an SCI in patient, recreationally active and athlete populations. We believe that an understanding of the impacts of exercise can provide a tool to help maintain or improve health in individuals with an SCI. A comprehensive literature search was conducted using the search engines PubMed, SPORTDiscus, Web of Science and Zetoc, search period June 2012-February 2013. Key words employed included spinal cord injury, immunology, exercise, paraplegic, tetraplegic, upper body exercise, interleukin, immunoglobulin, sympathetic, and parasympathetic. All articles and articles derived from their reference lists were checked for their suitability.

Hand-rim forces and gross mechanical efficiency at various frequencies of wheelchair propulsion.

To determine the effects of push frequency changes on force application, fraction of effective force (FEF) and gross efficiency (GE) during hand-rim propulsion. 8 male able-bodied participants performed five 4-min sub-maximal exercise bouts at 1.8 ms(-1); the freely chosen frequency (FCF), followed by 4 counter-balanced trials at 60, 80, 120 and 140% FCF. Kinetic data was obtained using a SMART(Wheel), measuring forces and moments. The GE was determined as the ratio of external work done and the total energy expended. Increased push frequency led to reductions in peak resultant force (P<0.05), ranging from 167 to 117 N and peak tangential force (P<0.05), ranging from 117 to 77 N. However, FEF only demonstrated a significant difference between 60% and 140% FCF (69 ± 9% and 63 ± 7, respectively; P<0.05). Work per cycle decreased significantly (P<0.05) and rate of force development increased significantly (P<0.05) with increased push frequency. GE values were significantly lower at 60%, 120% and 140% FCF than 80% and 100% FCF (P<0.05). No meaningful associations were present between FEF and GE. Under the current testing conditions, changes in push frequency are accompanied with changes in the absolute force values, albeit without changes in either the gross pattern/trend of force application or FEF. Changes in GE are not explained by different levels of force effectiveness.

Submaximal exercise responses in tetraplegic, paraplegic and non spinal cord injured elite wheelchair athletes.

It remains unclear whether similar exercise prescription, based on physiological markers, can be applied to subgroups of wheelchair athletes with different disabilities. Therefore, 25 wheelchair athletes, divided into three subgroups [eight tetraplegic (TETRA), nine paraplegic (PARA) and eight non spinal cord injured (NON-SCI)], performed an exercise test consisting of incremental submaximal stages, covering a range from 40% to 80% peak oxygen uptake (%VO(2peak) ). Oxygen uptake (VO(2)), heart rate (HR), blood lactate concentration (BLa) and rating of perceived exertion (RPE) were obtained for each stage. Expressed as a function of BLa, no differences were found between subgroups with respect to %VO(2peak) (group mean ± SD: 1.0 mmol/L: 53.9 ± 9.9%; 2.0 mmol/L: 70.7 ± 7.5%; 3.0 mmol/L: 78.5 ± 7.7%) and RPE [group mean (lower and upper quartile): 1.0 mmol/L: 10.8 (9.9, 12.2); 2.0 mmol/L: 13.6 (12.7, 14.3); 3.0 mmol/L: 14.9 (13.7, 16.5)]. Furthermore, no differences were found in the coefficient of determination (R(2) ) of the HR-VO(2) relationship in any of the subgroups (TETRA: 0.90 ± 0.12; PARA: 0.97 ± 0.02; NON-SCI: 0.96 ± 0.04). These results suggest that exercise prescription using measurements of VO(2), BLa or RPE can be based on the same recommendations in all the subgroups studied. This finding has added value for TETRA athletes, as it offers alternatives to HR monitoring.

Mucosal immune responses during court training in elite tetraplegic athletes.

STUDY DESIGN: Experimental study. OBJECTIVES: To examine salivary secretory immunoglobulin A (sIgA) responses and α-amylase activity during court training in highly trained tetraplegic athletes. SETTING: Loughborough, UK. METHODS: Seven highly trained wheelchair rugby athletes with tetraplegia performed two separate wheelchair rugby court training sessions, lasting 23 and 41.5 min, respectively, with either an aerobic or an interval focus. Timed, unstimulated saliva samples were obtained pre, post and 30 min post exercise and analysed for sIgA and α-amylase. Furthermore, blood lactate concentration and rating of perceived exertion (RPE) immediately after training were measured. RESULTS: sIgA secretion rate and α-amylase were unaffected by exercise during both sessions. However, the increases of sIgA concentration (30 min post exercise: +67 ± 29%) during the aerobic session were accompanied by decreases in saliva flow rate (-35 ± 22%). Athletes' physiological responses to exercise document the highly strenuous nature of the sessions, with blood lactate concentrations reaching 8.1 ± 1.0 and 8.7 ± 1.6 mmol l(-1) and RPE reaching 18(17,18) and 16(15,17) for the aerobic and the interval session, respectively. CONCLUSION: Acute bouts of highly strenuous exercise do not have negative impacts on the mucosal immune response in tetraplegic athletes, nor do they influence the production of α-amylase, a marker of sympathetic nervous activity. This contrasts responses previously observed in able-bodied athletes. The disruption of the sympathetic nervous system may prevent the downregulation of sIgA secretion rate following intense exercise, which is a response previously observed in able-bodied athletes.

Influence of varied tempo music on wheelchair mechanical efficiency following 3-week practice.

The purpose of this study was to analyse adaptations in propulsion technique and gross efficiency in novice able-bodied subjects during the initial phase of learning hand-rim wheelchair propulsion to music. 22 able bodied participants performed wheelchair propulsion (1.1 m·s(-1)) followed by a VO(2) peak test on a wheelchair ergometer. Push frequency, gross efficiency (GE), heart rate, rating of perceived exertion and propulsion technique variables (force application and temporal characteristics) were recorded. Participants were then assigned to a 3-wk practice period listening to i) 125 beats·min(-1) tempo music (LOW); ii) 170 beats·min(-1) tempo music (HIGH); or iii) a control group (CON). Following practice, all participants repeated the pre-testing protocol whilst force application data was collected in practice trials 1 and 9. After accounting for the pre-practice differences in GE (using ANCOVA), GE was higher in LOW compared with CON (P=0.038; 6.6 vs. 6.1% respectively). The differences between CON vs. HIGH and LOW vs. HIGH (P=0.830; P=0.188) were trivial suggesting that only LOW experienced an increase in GE. Practice had a favourable effect on the perceptions of effort, work per cycle, push and cycle time in contrast to the CON group. The use of music in a rehabilitation setting warrants further investigation.

Cooling strategies improve intermittent sprint performance in the heat of athletes with tetraplegia.

BACKGROUND: Precooling has been shown to enhance performance in repeated sprint exercise in able-bodied subjects in a hot environment. Spinal cord injury causes thermoregulatory impairment with a detrimental effect on performance. This study assessed whether cooling strategies before and during exercise in the heat enhances sprint performance in athletes with tetraplegia. METHODS: Eight male athletes with tetraplegia performed intermittent arm crank exercise in the heat (32.0 degrees C (0.1 degrees C); humidity, 50% (0.1%)) for a maximum of 60 min or until exhaustion. Trials involved a no-cooling control (CON), precooling (PRE) or cooling during exercise (DUR). Each intermittent sprint protocol consisted of varied periods of passive rest, maximal sprinting and active recovery. RESULTS: Both PRE and DUR cooling strategies improved the ability of the athletes to repeatedly perform high-intensity sprints, with times to exhaustion (TTE), whereas during the CON trial, athletes demonstrated a reduction in the total number of sprints and TTE (47.2 (10.8), 52.8 (5.8) and 36.2 (9.6) min for CON, PRE and DUR, respectively). Core temperature was significantly higher for CON (37.3 degrees C (0.3 degrees C)) when compared with both PRE and DUR (36.5 degrees C (0.6 degrees C) and 37.0 degrees C (0.5 degrees C), respectively, p<0.01). Ratings of perceived exertion and thermal sensation upon exhaustion or completion were not different. CONCLUSIONS: Athletes with tetraplegia should use a precooling or during-exercise cooling strategy specific to the characteristics of their sport when exercising in hot conditions.

Evaporative heat loss insufficient to attain heat balance at rest in individuals with a spinal cord injury at high ambient temperature.

The aim of the study was to determine whether climatic limits for achieving heat balance at rest are affected by spinal cord injury (SCI). Twenty-three men [8 able-bodied (AB), 8 with paraplegia (PP), and 7 with tetraplegia (TP)] rested in 37°C and 20% relative humidity (RH) for 20 min. With the ambient temperature held constant, RH was increased by 5% every 7 min, until gastrointestinal temperature (Tgi) showed a clear inflection or increased by >1°C. Tgi, skin temperatures, perceptual responses, and metabolic energy expenditure were measured throughout. Metabolic heat production [AB: 123 (21) W, PP: 111 (15) W, TP: 103 (29) W; means (SD)] and required rate of evaporative cooling for heat balance [Ereq; AB: 113 (20) W, PP: 107 (17) W, TP: 106 (29) W] were similar between groups (P = 0.22 and P = 0.79). Compared with AB, greater increases in Tgi were observed in TP (P = 0.01), with notable increases in mean skin temperature (Tsk) for TP and PP (P = 0.01). A Tgi inflection point was demonstrated by seven AB, only three of eight PP, and no TP. Despite metabolic heat production (and Ereq) being similar between groups, evaporative heat loss was not large enough to obtain heat balance in TP, linked to a shortfall in evaporative cooling potential. Although PP possess a greater sweating capacity, the continual increase in Tgi and Tsk in most PP, although lower than for TP, implies that latent heat loss for PP is also insufficient to attain heat balance.NEW & NOTEWORTHY In the absence of convective heat loss, at temperatures around 37°C evaporative heat loss is insufficient to attain heat balance at rest in individuals with paraplegia and tetraplegia. This finding was directly linked to a shortfall in evaporative cooling potential compared with required evaporative cooling. In this environment, individuals with both paraplegia and tetraplegia cannot subjectively determine the magnitude of their thermal strain; thus perceptual responses should not be relied upon for this population group.

Speed profiles in wheelchair court sports; comparison of two methods for measuring wheelchair mobility performance.

Wheelchair mobility performance is an important aspect in most wheelchair court sports, commonly measured with an indoor tracking system or wheelchair bound inertial sensors. Both methods provide key wheelchair mobility performance outcomes regarding speed. In this study, we compared speed profiles of both methods to gain insight into the level of agreement, for recommendations regarding future performance measurement. Data were obtained from 5 male highly trained wheelchair basketball players during match play. Players were equipped simultaneously with a tag on the footplate for the indoor tracking system (∼8 Hz) and inertial sensors on both wheels and frame (199.8 Hz). Being part of a larger study on 3 vs 3 player game formats, data were collected in several matches with varying field sizes, but activity profiles closely resembled regular match play. Both systems provide similar outcomes regarding distance covered and average speed. Due to differences in sampling frequency and sensor location (reference point) on the wheelchair (for speed calculation), minor differences were revealed at low speeds (<2.5 m/s). Since both systems provide complementary features, a hybrid solution as proved feasible in this study, could possibly serve as the new gold standard for mobility performance measurement in wheelchair basketball or wheelchair court sports in general.

Effects of two cooling strategies on thermoregulatory responses of tetraplegic athletes during repeated intermittent exercise in the heat.

Athletes with spinal cord injury (SCI), and in particular tetraplegia, have an increased risk of heat strain and consequently heat illness relative to able-bodied individuals. Strategies that reduce the heat strain during exercise in a hot environment may reduce the risk of heat illness. To test the hypotheses that precooling or cooling during intermittent sprint exercise in a heated environment would attenuate the rise in core temperature in tetraplegic athletes, eight male subjects with SCI (lesions C(5)-C(7); 2 incomplete lesions) undertook four heat stress trials (32.0 +/- 0.1 degrees C, 50 +/- 0.1% relative humidity). After assessment of baseline thermoregulatory responses at rest for 80 min, subjects performed three intermittent sprint protocols for 28 min. All trials were undertaken on an arm crank ergometer and involved a no-cooling control (Con), 20 min of precooling (Pre), or cooling during exercise (Dur). Trials were administered in a randomized order. After the intermittent sprint protocols, mean core temperature was higher during Con (37.3 +/- 0.3 degrees C) compared with Pre and Dur (36.5 +/- 0.6 degrees C and 37.0 +/- 0.5 degrees C, respectively; P < 0.01). Moreover, perceived exertion was lower during Pre (13 +/- 2; P < 0.01) and Dur (12 +/- 1; P < 0.01) compared with Con (14 +/- 2). These results suggest that both precooling and cooling during intermittent sprint exercise in the heat reduces thermal strain in tetraplegic athletes. The cooling strategies also appear to show reduced perceived exertion at equivalent time points, which may translate into improved functional capacity.

The intra-push velocity profile of the over-ground racing wheelchair sprint start.

The aim of this study was to analyse the first six pushes of a sprint start in over-ground racing wheelchair propulsion. One international male wheelchair athlete (age=28 years; body mass=60.6 kg; racing classification=T4) performed maximal over-ground sprint trials, over approximately 10 m, in his own racing wheelchair fitted with a velocometer. Each trial was filmed at 200 Hz using a "Pan and Tilt" system. Eight trials were manually digitised at 100 Hz. Raw co-ordinate data were smoothed and differentiated using a quintic spline routine. Across the period from pushes one to six the duration of each push cycle decreased (0.82+/-0.02-0.45+/-0.01 s) with the mean duration of the propulsive phase decreasing from 0.62+/-0.02 to 0.21+/-0.01 s and the recovery phase increasing from 0.20+/-0.01 to 0.24+/-0.02 s. The push-rim was contacted progressively closer to top dead centre and released progressively closer to bottom dead centre with each push. The data indicate that peak velocity occurred after release. The main findings of this study support the observation that racing wheelchair sprint propulsion is a complex form of locomotion and cannot be described accurately by using just the established definitions of a propulsive and a recovery phase.

Influence of wheel configuration on wheelchair basketball performance: wheel stiffness, tyre type and tyre orientation.

The aim of the current investigation was to explore the lateral stiffness of different sports wheelchair wheels available to athletes in 'new' and 'used' conditions and to determine the effect of (a) stiffness, (b) tyre type (clincher vs. tubular) and (c) tyre orientation on the physiological and biomechanical responses to submaximal and maximal effort propulsion specific to wheelchair basketball. Eight able-bodied individuals participated in the laboratory-based testing, which took place on a wheelchair ergometer at two fixed speeds (1.1 and 2.2 m s(-1)). Outcome measures were power output and physiological demand (oxygen uptake and heart rate). Three participants with experience of over-ground sports wheelchair propulsion also performed 2 × 20 m sprints in each wheel configuration. Results revealed that wheels differed significantly in lateral stiffness with the 'new' Spinergy wheel shown to be the stiffest (678.2 ± 102.1 N mm(-1)). However the effects of stiffness on physiological demand were minimal compared to tyre type whereby tubular tyres significantly reduced the rolling resistance and power output in relation to clincher tyres. Therefore tyre type (and subsequently inflation pressure) remains the most important aspect of wheel specification for athletes to consider and monitor when configuring a sports wheelchair.

A kinetic analysis of trained wheelchair racers during two speeds of propulsion.

The purpose of the study was to investigate the propulsion kinetics of wheelchair racers at racing speeds and to assess how these change with an increase in speed. It was hypothesised that propulsive force would increase in proportion to speed, to accommodate the additional work required. Six wheelchair racers volunteered to participate in this study which required each athlete to push a racing wheelchair at 4.70 and 5.64 m s(-1) on a wheelchair ergometer (WERG). Eight pairs (16 in total) of strain gauges, mounted on four bars attached to the hand-rim of a racing wheelchair wheel, measured the medio-lateral and tangential forces applied to the hand-rim. Kinetic data were sampled at 200 Hz while a single on-line (ELITE) infrared camera operating at 100 Hz was positioned perpendicular to the WERG to record the location of the hand with respect to the hand-rim. In general, peak tangential force occurred when the hand was positioned on the hand-rim between 140 and 180 degrees. With the increase in speed, the peak hand-rim forces applied tangentially increased from 132 to 158 N and those applied medio-laterally increased from 90 to 104 N. The ratio of tangential to total measured force was similar at both speeds (80 and 82%, respectively). In conclusion, these data indicate that wheelchair racers adopt a different propulsion strategy than that employed in everyday chairs and that the forces increase in proportion to propulsion speed.

Influence of glove type on mobility performance for wheelchair rugby players.

OBJECTIVE: The purpose of this study was to determine the effectiveness of different glove types on mobility performance in a series of field tests specific to wheelchair rugby. DESIGN: Ten international wheelchair rugby players performed three drills in each glove condition: (i) players' current glove selection, (ii) American football glove, (iii) building glove, and (iv) new prototype glove. Performance was assessed by a combination of outcomes including test times, peak velocities, and accelerations within each drill. Peak velocities and accelerations were measured using a velocometer sampling at 100 Hz. RESULTS: A two-way analysis of variance with repeated measures revealed that participants performed statistically better for measures of acceleration and sprinting when wearing their current choice of glove compared with the new prototype glove (P < 0.05). Subjective data identified that players also favored their current gloves compared with others, although slight discrepancies were evident among classification levels concerning the building gloves. Building gloves seemed to be less suited to low-point players because of the reduced grip and protection they provided. CONCLUSIONS: It may be concluded that participants' current gloves that have been modified for the specific demands of wheelchair rugby are more effective for aspects of mobility performance than other glove types.

Efficiency of wheelchair propulsion and effects of strategy.

The purpose of this study was to determine the contributions of arm frequency and propulsion mode on the internal work during submaximal wheelchair propulsion. Twelve able-bodied participants performed a V.O (2) peak test on a wheelchair ergometer. On a separate occasion, six (4 min) submaximal exercise conditions employing two modes of propulsion (synchronous, SYN vs. asynchronous, ASY) at arm frequencies of 40 and 80 rev . min (-1) were performed at 1.2 m . s (-1) and 1.7 m . s (-1). These conditions resulted in three push strategy combinations (ASY [20 : 20], SYN [40 : 40] & ASY [40 : 40]) at two speeds. Gross, net, work and delta efficiency were determined. The cost of unloaded exercise was significantly lower for the ASY [20 : 20] than both ASY and SYN [40 : 40] (0.49 vs. 0.58 and 0.57 L . min (-1), respectively). All the efficiency indices decreased as velocity increased (p < 0.01). ASY [20 : 20] was the least efficient (gross and work) mode (4.2 +/- 0.4 % and 6.2 +/- 0.8 % respectively). Comparison of equal arm frequencies (ASY [40 : 40] vs. SYN [40 : 40]); found the efficiency to be lower for ASY propulsion (p < 0.05). Under the current testing conditions SYN propulsion mode offers greater efficiency during wheelchair propulsion.

Biomechanics and energetics of basketball wheelchairs evolution.

The aim of this study was to investigate metabolic demand and mechanical work of different basketball wheelchairs that represented significant stages of its evolution from 1960 to date. Four subjects pushed each model on a basketball court at different speeds (from 0.90 to 2.35 m.s(-1)). During the trials, oxygen consumption was measured. Also, the different forms of mechanical work involved in the exercise were investigated. The oxygen consumption decreased from the oldest model to the next ones, remaining then quite constant. This was also the same with breathing and pushing frequencies. Both the work against air drag and rolling resistance decreased, air drag always played a minor role due to the low speeds investigated. The total mechanical work was highest in the oldest wheelchair and lowest in the newest one. The efficiencies were found similar for all the chairs but the most recent one (less efficient). Already by the 1970's the wheelchair economy had reached an acceptable level, at least partially because of its improved ergonomics. Yet, when focusing on the efficiency, the surprisingly low value with the newest model suggests factors other than the economy (need of better balance, responsiveness, and ground grip) as determinants of the evolution of this device.

Oxygen uptake-heart rate relationship in élite wheelchair racers.

The American College of Sports Medicine (ACSM) recommends that, as a general rule for health purposes, individuals should exercise at 40%-85% of their maximal oxygen uptakes. Moreover, it has been suggested that 55%-90% of the maximal heart rate may be used as an alternative estimate of these percentage maximal oxygen uptake values. The present study examined the relationship between percentage peak heart rate (% HRpeak) and percentage peak oxygen uptake (% VO2peak) during steady-state incremental intensity wheelchair propulsion of 16 élite, male wheelchair racers (WR). Oxygen uptake was determined during each submaximal exercise stage and heart rate (HR) was continuously monitored. The VO2peak was subsequently determined using a separate protocol. Linear regression equations of % HRpeak versus % VO2peak for each participant included % HRpeak values corresponding to 40%, 60%, 80% and 85% VO2peak. The linear regression equation, derived as the group mean of the slope and intercept terms determined for each individual, was: % peak HR = 0.681 x % peak VO2 + 33.2. The group mean of the individual correlation coefficients for the VO2-HR relationship was 0.99. The values of % HRpeak for each of the % VO2peak values below 85% were significantly greater (P<0.01) than those suggested by the ACSM. This suggests that the ACSM guidelines below 85% VO2peak, based on % HRpeak, may underestimate the relative exercise intensity (i.e. % VO2peak) in the WR population. However, in élite level WR, % HRpeak can be recommended as an alternative estimate of % VO2peak at wheelchair propulsion intensities of 85% VO2peak or more.