John P. Lenton

Regulating intensity using perceived exertion in spinal cord-injured participants

PURPOSE To examine the validity of perception-based intensity regulation during handcycling exercise. METHODS Eight spinal cord-injured (T11 incomplete to T4 complete) participants completed an incremental exercise test followed by a (.)VO2peak test using a sports hand bike. Subsequently, two 20-min exercise tests were completed at an individualized power output (PO) at moderate and vigorous intensities (50% and 70% of (.)VO2peak, respectively). On a separate occasion, participants were instructed to produce and maintain a workload equivalent to the average RPE for the 20-min imposed condition in a counterbalanced order. The (.)VO2 and blood lactate concentration [BLa(-)] were measured every 10 min, and HR and PO were measured at 1-min intervals. RESULTS There were no differences in average (.)VO2, percent V O2peak, HR, PO, and [BLa(-)] between the imposed PO conditions and RPE-regulated trials of either exercise intensity. Although PO increased slightly during the moderate-intensity RPE-regulated trial (P < 0.04), it remained relatively constant in the vigorous RPE-regulated trial. However, there was a tendency for PO to be slightly higher (P = 0.07) in the vigorous RPE-regulated trial. CONCLUSIONS These data suggest that RPE is effective in controlling moderate and vigorous intensities throughout a 20-min handcycling exercise session for SCI participants.

Wheelchair propulsion: effects of experience and push strategy on efficiency and perceived exertion

The purpose of this study was to examine the role of wheeling experience on efficiency, metabolic cost, and differentiated ratings of perceived exertion (RPEs) during synchronous and asynchronous hand-rim propulsion with varying arm frequencies. Fourteen able-bodied (AB) male participants and 8 male wheelchair sportsmen (WS) performed tests of peak oxygen consumption for both propulsion modes. Subsequently, 2 series of five 4-min sub-maximal exercise bouts were completed at an individualized velocity (60% of peak oxygen consumption). Arm frequencies consisted of the freely chosen frequency (FCF), followed by 4 counter-balanced paced trials pushing at 60%, 80%, 120%, and 140% of the FCF. Efficiency indices (gross, GE; work, WE) were determined and peripheral (RPE-P), central (RPE-C), and overall (RPE-O) RPEs were recorded. The GE (6.4% vs. 8.4%) and WE (11.3% vs. 15.1%) were significantly higher in WS than in AB (p = 0.001). Trends in the oxygen consumption, GE, and WE data were similar in both groups, propulsion mode, and arm frequency. Data suggest that 80% FCF resulted in improved efficiency for both propulsion mode and group, although the differences between those arm frequencies immediately above and below were non-significant. Lower RPE scores corresponded with higher efficiency values. Regardless of group there were significant differences (p = 0.001) between the differentiated RPE measures, whereby RPE-P was on average always the highest score (13.1) and RPE-C the lowest (11.1; RPE-O was 12.2). In conclusion, despite the anticipated differences in efficiency between the WS and AB participants, this study confirmed that psycho-physiological measures produce similar trends to physiological measures with manipulations of both arm frequency and propulsion mode.

Spinal Cord Injury Level and the Circulating Cytokine Response to Strenuous Exercise

PURPOSE A complete spinal cord injury (SCI) above the sixth thoracic vertebra (T6) results in the loss of sympathetic innervation of the adrenal medulla. This study examined the effect of a complete SCI above and below T6 on plasma concentrations of epinephrine, circulating interleukin 6 (IL-6) and other inflammatory cytokines in response to acute strenuous exercise. METHODS Twenty-six elite male wheelchair athletes (8 = C6-C7 tetraplegic [TETRA], 10 = T6-L1 paraplegic [PARA], and 8 = non-spinal-cord-injured controls [NON-SCI]) performed a submaximal exercise test followed by a graded exercise to exhaustion on a motorized treadmill. Blood samples were taken preexercise, postexercise, and 30 min postexercise and analyzed for concentrations of IL-6, IL-10, IL-1 receptor antagonist (IL-1ra), tumor necrosis factor α (TNF-α), epinephrine, and cortisol. RESULTS The circulating IL-6 concentration was significantly elevated at postexercise and 30 min postexercise (post30; approximately fivefold) in NON-SCI and PARA (P = 0.003), whereas concentrations in TETRA did not change significantly from preexercise values. IL-10, IL-1ra, and TNF-α were unaffected by exercise in all groups; however, both SCI groups presented elevated concentrations of IL-10 compared with NON-SCI (P = 0.001). At postexercise, epinephrine concentrations were significantly higher than preexercise and post30 concentrations in NON-SCI (approximately threefold) and PARA (approximately twofold) (P = 0.02). Plasma epinephrine concentrations were unchanged in TETRA throughout exercise; concentrations were significantly lower than NON-SCI and PARA at all time points. Plasma cortisol concentrations were significantly elevated in all groups at postexercise and post30 compared with preexercise (P < 0.001). Total exercise time was similar between groups (NON-SCI = 38 ± 6; PARA = 35 ± 5; TETRA = 36 ± 5 min). CONCLUSIONS These findings suggest that the sympathetic nervous system plays an important regulatory role in the circulating IL-6 response to exercise and has implications for the metabolic and inflammatory responses to exercise in individuals with injuries above T6.

A physiological and biomechanical comparison of over-ground, treadmill and ergometer wheelchair propulsion

Abstract The purpose of the study was to determine which laboratory-based modality provides the most valid physiological and biomechanical representation of over-ground sports wheelchair propulsion. Fifteen able-bodied participants with previous experience of wheelchair propulsion performed a 3-minute exercise trial at three speeds (4, 6 and 8 km ∙ h–1) in three testing modalities over separate sessions: (i) over-ground propulsion on a wooden sprung surface; (ii) wheelchair ergometer propulsion; (iii) treadmill propulsion at four different gradients (0%, 0.7%, 1.0% and 1,3%). A 0.7% treadmill gradient was shown to best reflect the oxygen uptake (7.3 to 9.1% coefficient of variation (CV)) and heart rate responses (4.9 to 6.4% CV) of over-ground propulsion at 4 and 6 km ∙ h–1. A 1.0% treadmill gradient provided a more valid representation of oxygen uptake during over-ground propulsion at 8 km ∙ h–1 (8.6% CV). Physiological demand was significantly underestimated in the 0% gradient and overestimated in the 1.3% gradient and wheelchair ergometer trials compared to over-ground trials (P<0.05). No laboratory-based modality provided a valid representation of the forces applied during OG (≥ 18.4% CV). To conclude, a 0.7% treadmill gradient is recommended to replicate over-ground wheelchair propulsion at lower speeds (4 and 6 km ∙ h–1) whereas a 1.0% gradient may be more suitable at 8 km ∙ h–1.

Criterion validity and accuracy of global positioning satellite and data logging devices for wheelchair tennis court movement

Abstract Purpose To compare the criterion validity and accuracy of a 1 Hz non-differential global positioning system (GPS) and data logger device (DL) for the measurement of wheelchair tennis court movement variables. Methods Initial validation of the DL device was performed. GPS and DL were fitted to the wheelchair and used to record distance (m) and speed (m/second) during (a) tennis field (b) linear track, and (c) match-play test scenarios. Fifteen participants were monitored at the Wheelchair British Tennis Open. Results Data logging validation showed underestimations for distance in right (DLR) and left (DLL) logging devices at speeds >2.5 m/second. In tennis-field tests, GPS underestimated distance in five drills. DLL was lower than both (a) criterion and (b) DLR in drills moving forward. Reversing drill direction showed that DLR was lower than (a) criterion and (b) DLL. GPS values for distance and average speed for match play were significantly lower than equivalent values obtained by DL (distance: 2816 (844) vs. 3952 (1109) m, P = 0.0001; average speed: 0.7 (0.2) vs. 1.0 (0.2) m/second, P = 0.0001). Higher peak speeds were observed in DL (3.4 (0.4) vs. 3.1 (0.5) m/second, P = 0.004) during tennis match play. Conclusions Sampling frequencies of 1 Hz are too low to accurately measure distance and speed during wheelchair tennis. GPS units with a higher sampling rate should be advocated in further studies. Modifications to existing DL devices may be required to increase measurement precision. Further research into the validity of movement devices during match play will further inform the demands and movement patterns associated with wheelchair tennis.

Effects of Arm Frequency during Synchronous and Asynchronous Wheelchair Propulsion on Efficiency

To further understand the possible underlying mechanisms of the low efficiencies in hand rim wheelchair propulsion, this study examined efficiency indices at different arm frequencies during two propulsion modes (synchronous and asynchronous). Fourteen male able-bodied participants performed VO2PEAK tests for both propulsion modes. Subsequently two sub-maximal exercise tests examining synchronous and asynchronous propulsion were completed at an individualised velocity (60% of VO2PEAK). The freely chosen arm frequency (FCF), followed by four counter-balanced trials at 60, 80, 120, and 140% of FCF were performed. Gross, net, and work efficiency were determined. Gross efficiency was significantly lower (p<0.05) at arm frequencies >100%, and participants were more efficient between 60 to 100% FCF. These arm frequencies corresponded to 76+/-22 to 126+/-36 and 70+/-18 to 116+/-30 pushes x min(-1) (synchronous and asynchronous respectively). Trends in VO2, gross and work efficiency suggest that 80% of FCF produced the best economy and efficiency during both propulsion modes (non-significant). Gross and work efficiency at 80% FCF were 6.8+/-0.7% and 13.0+/-4.6% for synchronous and 7.0+/-0.8% and 11.5+/-1.6% for asynchronous respectively. The results suggest that during both modes of propulsion the FCF is not necessarily the most efficient.

Effects of Wheel and Hand-rim Size on Submaximal Propulsion in Wheelchair Athletes

PURPOSE This study aimed to investigate the effects of fixed gear ratio wheel sizes on the physiological and biomechanical responses to submaximal wheelchair propulsion. METHODS Highly trained wheelchair basketball players (N = 13) propelled an adjustable sports wheelchair in three different wheel sizes (24, 25, and 26 inches) on a motor-driven treadmill. Each wheel was equipped with force-sensing hand-rims (SMARTWheel), which collected kinetic and temporal data. Oxygen uptake (V˙O2) and HR responses were measured with high-speed video footage collected to determine three-dimensional upper body joint kinematics. RESULTS Mean power output and work per cycle decreased progressively with increasing wheel size (P < 0.0005). Increasing wheel size also reduced the physiological demand with reductions in VO2 for 25-inch (0.90 ± 0.20 L · min(-1), P = 0.01) and 26-inch wheels (0.87 ± 0.16 L · min(-1), P = 0.001) compared with 24-inch wheels (0.98 ± 0.20 L · min(-1)). In addition, reductions in HR were observed for 26-inch wheels (99 ± 6 beats · min(-1)) compared with 25-inch (103 ± 8 beats · min(-1), P = 0.018) and 24-inch wheels (105 ± 9 beats · min(-1), P = 0.004). Mean resultant forces also decreased progressively with increasing wheel size (P < 0.0005). However, no changes in temporal or upper body joint kinematics existed between wheel sizes. CONCLUSIONS A greater power requirement owing to a greater rolling resistance in 24-inch wheels increased the physiological demand and magnitude of force application during submaximal wheelchair propulsion.

Effects of 4-weeks of asynchronous hand-rim wheelchair practice on mechanical efficiency and timing

Purpose. To investigate the consequence on gross mechanical efficiency (GE), arm frequency and sub-maximal performance, of paced and unpaced practice during asynchronous hand-rim wheelchair propulsion. Methods. Twenty-five able-bodied participants performed five, 4-min exercise bouts at 1.7 m/s, at the freely chosen frequency (FCF) and four paced arm frequencies of 60, 80, 120 and 140% FCF. GE, arm frequency and measures of sub-maximal performance were determined. Participants were assigned to an unpaced (FCF, N = 9), paced (80% FCF, N = 8) or control (CON, N = 8) no practice group. The FCF and 80% FCF groups received 4-weeks (unpaced and paced, respectively) propulsion practice (three sessions·per wk, four 4 min/trials; 33–35 W) at 1.7 m/s on a wheelchair ergometer. Following practice, the pre-testing protocol was repeated. Results. Mean GE showed a relative increase in both experimental groups (21 and 17%; FCF and 80% FCF respectively; p = 0.001) compared to no change in CON (−1.5%). The FCF arm frequency decreased in both experimental groups (p = 0.001), with larger changes evident following FCF practice. Conclusion. Four weeks of unpaced or paced practice had a beneficial effect on GE. This improvement seems to be associated with a reduction in arm frequency.

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.

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.