Muscular Efficiency During Arm Cranking and Wheelchair Exercise: A Comparison Training & Testing 408
Abstract The present study was performed to compare various individual muscular efficiency indices, i. e., gross (GE), net (NE), work (WE), and delta (DE), during arm cranking ergometer (ACE) and wheelchair ergometer (WERG) exercise at the same relative exercise intensities. Following a maximal test on both the ACE and WERG, 15 able-bodied subjects completed 4 submaximal bouts at 0, 40, 55 and 70 % of the mode-specific V˙O2peak. The peak power output and V˙O2 values were significantly higher with ACE than WERG maximal exercise. As a consequence, the power output imposed during WERG submaximal bouts was significantly lower compared to ACE submaximal bouts. ACE exercise was found to elicit a significantly higher (p < 0.001) V˙O2 (16 to 28 vs 14 to 23 ml N min–1 N kg–1), GE (9 to 11 vs 6 to 9 %) and NE
Introduction The arm cranking (ACE) and the hand-rim propulsion on a wheelchair (WERG) are two modes of propulsion involving the upper limb muscles. But the arm movements are rather different in accordance with the system of propulsion used. The ACE propulsion is an asynchronous bilateral action of the arms whereas the WERG propulsion is a simultaneous action of the arms divided in active and passive periods [15]. The biomechanical and physiological comparisons between these two modes of propulsion have interested the researchers in order to determine the most efficient system [5,11,13,16]. Oxygen consumption (V˙O2), pulmonary ventilation and heart rate are commonly used to compare energy demand during ACE and WERG submaximal ex-
F. Hintzy1 N. Tordi2 S. Perrey2
(14 to 13 vs 10 to 11 %) compared to WERG exercise at power output from 40 to 70 % V˙O2peak, respectively. However, WE (17 to 15 vs 17 to 14 % at 40 to 55 % V˙O2peak) and DE (12 to 13 vs 12 to 12 % at D40 – 55 % to D55 – 70 % V˙O2peak) values were similar between ACE and WERG exercise. The lower GE and NE observed during WERG compared to ACE exercise could be explained by the biomechanical disadvantages of the hand-rim WERG pattern movement. These findings also supported that the different indices of efficiency influenced the interpretation of the comparison between ACE and WERG propulsion. Key words Maximal exercise · submaximal exercise · gross efficiency · net efficiency · work efficiency · delta efficiency · relative intensity · healthy male subjects
ercise. When the comparison is realized at a given absolute intensity (i. e., similar power output [PO] for both ACE and WERG exercise), the energy demand is higher during WERG compared to ACE exercise [5,13,16]. As a result, the gross efficiency (GE: ratio of external work to total energy expended) and the net efficiency (NE: ratio of external work to total energy expended above rest) are lower during WERG compared to ACE exercise [10,16, 20]. The lower GE and NE in WERG exercise have been explained by the small muscle mass of the arms involved [16], and by the biomechanical disadvantages of using hand-rims to propel the wheelchair [16, 20]. Nevertheless, impose a same PO during ACE and WERG exercise represented probably a higher relative intensity during WERG than ACE due to the higher PO peak values observed during ACE compared to WERG, whatever the
Affiliation 1 Laboratoire de Mod6lisation des Activit6s Sportives (LMAS), Le Bourget du lac, France 2 Laboratoire des Sciences du Sport, Besanc¸on, France Correspondence F. Hintzy, PhD · Laboratoire de Mod6lisation des Activit6s Sportives (LMAS) · D6partement STAPS, UFR CISM · Campus universitaire · 73376 Le Bourget du Lac · France · Phone: +33 (479) 758146 · Fax: +33 (479) 758148 · E-Mail:
[email protected] Accepted after revision Bibliography Int J Sports Med 2002; 23: 408–414 I Georg Thieme Verlag Stuttgart · New York · ISSN 0172-4622
Method
Hintzy F et al. Muscular Efficiency During … Int J Sports Med 2002; 23: 408 – 414
Subjects Fifteen able-bodied male volunteers participated in both ACE and WERG exercise after having given their written informed consent. All subjects had no experience in ACE and WERG exercise and were not trained in upper body sport activities. These subjects were (mean P SD) 23 P 2 yrs old and 179.3 P 4.0 cm tall, weighted 74.1 P 6.3 kg, and had 11.5 P 2.0 % body fat. Experimental protocol Prior to experimental testing, each subject performed several practice sessions on ACE and WERG ergometer. The experimental protocol consisted of four tests: an incremental maximal test and a submaximal test on the two ergometers. The maximal test preceded the submaximal exercise bouts and the order of the two ergometer testing was randomly determined. The two maximal tests were separated by at least one week and the two submaximal tests were separated by at least three days. All tests were completed within a 3 weeks period. The Fig. 1 shows the schematic diagram of the experimental protocol. Continuous incremental maximal exercises were realized on each ergometer using identical test protocol: resistance was increased by 10 W every 2 min, with an initial PO of 20 W. For ACE, the crank rate was set at 60 rpm and for WERG, the velocity was fixed at 1.11m N s-1 with a free cycle-frequency. For ACE and WERG maximal exercise, loads were increased until volitional fatigue, i. e., failure to maintain the required velocity (P 10 %). The
Fig. 1 A schematic diagram of the experimental protocol.
usual criterion of a plateau or a decrease in V˙O2 with an increase in PO was used to determine the peak oxygen consumption (V˙O2peak) and the corresponding peak power output (POpeak) values [17]. Prior to each submaximal test, base-line resting data for oxygen consumption (V˙O2rest) were obtained following 10-min seated rest on ACE and WERG ergometer. Subjects then performed four submaximal steady-state bouts on the two ergometers. The PO corresponding to 0 (unloaded), 40, 55 and 70 % of mode-specific V˙O2peak were determined from each of the individual V˙O2-PO linear regression obtained during each maximal test [9]. The exercise at each workload was 4 min in duration, followed by a resting period of 10 min between bouts. An ascending order of intensity level was imposed. The frequency was 60 rpm during ACE [20] and the velocity was fixed at 1.11m N s-1 with a handrim frequency of 60 cycle N min-1 during WERG [7]. The velocity and the frequency imposed during WERG were close to the optimal velocity minimizing the energy expenditure and to the free cycle-frequency [7, 23], respectively. Each subject received auditory and visual pacing from a metronome during all tests. Verbal encouragement was offered during all tests to assist the subject in maintaining the desired cadence. Also, the subjects were asked to remain seated on the chair with their backs in contact with the backrests, in order to minimize trunk movements throughout ACE and WERG tests. During the practice sessions, instructions were given to the subjects about the position of the hands on the hand-rim and about the propulsion technique. Materials All subjects exercised on a friction-loaded arm cranking ergometer (Monark, 818E, Stockholm, Sweden) fixed to a table. The height of the seat was adjusted so that the scapula-humeral joint and the crank pedal axle were at the same level. The grip of the crankshaft was at the distal end when the subject fully extended his elbow in the horizontal plane [15]. The legs of the subjects were not braced, with the feet placed flat on the floor at premarked places to maintain high reproducibility of the subject’s posture. During the unloaded condition, the subjects cranked without a flywheel resistance. The wheelchair ergometer was composed of a standard wheelchair (Quickie EX, Sunrise, Medical, England) placed on a specific friction braked ergometer (VP100H TE, HEF, Tecmachine, Andrezieux Boutheon, France). This ergometer consisted of two parallel cylindrical rollers beneath the wheels, which produced the
Training & Testing
population studied [5,10,13,18, 30]. As a result, the disproportion of PO imposed could also partly explain the higher NE and GE observed during ACE than WERG exercise. For example, Kang et al. [9] have showed that ACE and cycle exercise induced similar GE and NE values at the same relative intensities whereas previous studies found higher GE and NE values during cycle compared to ACE exercise at the same absolute intensities [e. g., 19]. To our knowledge, direct comparisons of NE and GE between ACE and WERG exercise at the same relative intensities (i. e., intensity calculated in percentage of the individual mode-specific V˙O2peak values) have not been realized. In addition, the majority of the investigations studying these modes of propulsion have examined only GE and NE indices [2, 6 – 7,10,13,16, 20 – 21, 24, 28]. However, other muscular efficiency indices do exist, such as the work efficiency (WE) and the delta efficiency (DE), which differ in term of base-line subtraction from the total energy expenditure [4, 28]. The WE (i. e., the ratio of mechanical work accomplished to the energy expenditure above exercising without a load) and the DE (i. e., the change of energy expenditure relative to the change in work accomplished) are actually considered to be a more valid estimation of the true muscular efficiency since they take into account the unmeasured work [4, 28]. Due to the biomechanical disadvantages of WERG propulsion (high amount of unmeasured work), differences in values obtained for the various efficiency indices could enable us to more fully interpret comparisons between WERG and ACE propulsion. Therefore, the purpose of this study was to compare the muscular efficiency indices (GE, NE, WE and DE) between alternative arm cranking and simultaneous hand-rim wheelchair exercise at the same relative intensities for able-bodied subjects.
409
Training & Testing 410
braking torque by a hysteresis brake (Type ZS, Hysteresebremse ebu 11, Zahnradfabrik. Friedrichshafen, Germany). The angular speed of the roller was measured by an electric speed transducer mounted in contact with the roller (Type REO 110, Radio Energie, Massy, France). The PO was calculated with specific software as the product of the force exerted by the subject on the wheels (measured by the electromagnetic brake on the roller while taking into account the frictional losses, the inertia force and the braking torque) by the wheelchair velocity measured with the speed of the roller. The VP100H WERG ergometer was extensively detailed in Devillards et al. [3]. Moreover, the wheelchair was removed from the ergometer (with wheels not in contact with the rollers or the ground) during the unloaded condition. The velocity was controlled by an electric speed transducer placed on the wheels. The gas exchange variables were measured breath-by-breath using an automatic gas analyser system (Medical Graphics type CPX/D, St Paul, WI, USA). The gas analyser and the expiratory airflow volume were calibrated before and after each session by gases of known concentrations and a 3-l syringe, respectively.
GE ¼
W 100 E
NE ¼
W 100 E ER
WE ¼
Statistics Linear correlation coefficients were calculated to assess the interrelationships between peak values obtained during ACE and WERG exercise. A paired Student’s t-test was applied to assess the significance of differences in peak variables (V˙O2peak, POpeak, RERpeak) between ACE and WERG exercise. Significant differences in dependent variables measured during the submaximal bouts were analysed using a two-way (mode of propulsion N intensity) analysis of variance (ANOVA) with repeated measures. Post hoc comparisons using Scheff6 procedure followed the analysis of variance. In addition, a regression analysis was used to determine the relationship in the two modes of propulsion between PO and the following variables (V˙O2, GE, NE, WE, DE). The significance level was set at p < 0.05 for all statistical analyses.
Results Maximal test Table 1 presents the peak physiological responses and POpeak measured during both modes of propulsion. V˙O2peak (p < 0.001), RERpeak (p < 0.05) and POpeak (p < 0.001) were significantly lower during WERG compared with ACE exercise. In addition, a moderate but significant correlation coefficient was found for V˙O2peak (r2 = 0.3085; p < 0.05), RERpeak (r2 = 0.7909; p < 0.001) and POpeak (r2 = 0.3191; p < 0.05) between ACE and WERG exercise. Submaximal exercise bouts During ACE and WERG exercise, V˙O2rest was 4.81 P 0.11 and 4.83 P 0.10 ml N min–1 N kg–1 , and V˙O2unload was 6.73 P 0.51 and 8.40 P 0.44 ml N min–1 N kg-1, respectively. The PO corresponding to 40, 55 and 70 % of V˙O2peak, V˙O2 and the different values of efficiency indices calculated at each submaximal bout during ACE and WERG exercise are presented in Table 2. Effect of propulsion mode: V˙O2 rest was similar but V˙O2 unload was significantly higher (p < 0.001) during WERG compared to ACE exercise. WERG was found to elicit a significantly lower PO (p < 0.001), V˙O2 (p < 0.001), GE (p < 0.001) and NE (p < 0.001)
W 100 E EU
Table 1 W 100 DE ¼ E
Fig. 2 Equations used for calculating gross efficiency (GE), net efficiency (NE), work efficiency (WE) and delta efficiency (DE) indice. W is the external work accomplished (J $ min–1). E is the total energy expended (J $ min–1). ER is the energy expended at rest. EU is the energy ˙O2 unload. DW is expended during unloaded exercise, calculated from V the increment of work performed above the previous work rate. DE is the increment of energy expended above the previous energy expended.
Physiological responses during ACE and WERG maximal ˙O2peak: peak oxygen consumption, RERpeak: exercise. V peak respiratory exchange ratio, POpeak: peak power output. Values are means 3 SD. *Significantly different between ACE and WERG exercise, p < 0.05; ***: p < 0.001 ACE
˙O2peak (ml min–1 kg–1) V RERpeak POpeak (W)
38.92 4.01***
WERG 34.51 3.61
1.28 0.06*
1.26 0.06
111.33 9.9***
78.67 12.46
Hintzy F et al. Muscular Efficiency During … Int J Sports Med 2002; 23: 408 – 414
Measurements and calculations V˙O2 (in ml N min–1 N kg-1) and carbon dioxide output (VC˙O2 in ml N min–1 N kg–1) were measured continuously during maximal and submaximal tests and averaged every 15 s. Mean values of PO, V˙O2 and respiratory exchange ratio (RER, i. e., VC˙O2/V˙O2) attained during the last minute of each submaximal steady state exercise bouts were used for statistical analysis. V˙O2rest and V˙O2 corresponding to the unloaded exercise at 0 % (V˙O2unload) were calculated during the last minute of the resting and the unloaded periods, respectively. The mechanical efficiency of ACE and WERG propulsion is calculated as the ratio of the external work accomplished to the amount of the energy expended. For ACE and WERG exercise, the work accomplished was determined by the workload on the ergometer and converted in J N min–1. The energy expenditure was obtained from V˙O2 and converted to equivalent J N min–1 by using the associated measurements of RER and the standard conversion tables [1]. Depending on the base-line subtracted from the total energy expended, different mechanical efficiency indices were calculated [4, 28]. The equations used for calculating each of the efficiency indices are presented in Fig. 2.
Calculation of GE, NE and WE were made at each relative intensity (40, 55, 70 % V˙O2peak) for both ACE and WERG submaximal exercise bouts while DE calculation was made for each increment of exercise intensity, i. e., D40 – 55 % and D55 – 70 % V˙O2peak. Physiological variables were excluded from all efficiency calculations when RER values exceeded 1.0.
Table 2
˙O2), power output (PO) and differOxygen consumption (V ent efficiency indices (GE: gross efficiency, NE: net efficiency, WE: work efficiency, DE: delta efficiency) during ACE and WERG submaximal exercise at each relative in˙O2peak). Values are means 3 tensity (40 %, 55 %, 70 % V SD. *Significantly different between ACE and WERG exercise, p < 0.05; ***p < 0.001 % V˙O2peak
PO (W)
˙O2 (ml min–1 kg–1) V
NE (%)
WE (%)
DE (%)
WERG
40 %
37.87 4.45***
22.41 6.65
55 %
56.43 5.49***
36.82 7.15
70 %
74.92 6.90***
51.23 8.43
40 %
15.83 1.52***
13.70 1.68
55 %
22.00 2.07***
18.53 2.16
70 %
27.80 2.44***
23.22 2.48
40 %
9.50 0.71***
6.45 1.66
55 %
10.20 0.66***
7.88 1.23
70 %
10.71 0.65***
8.76 1.14
40 %
13.72 1.13***
9.93 2.19
55 %
13.10 0.97***
10.69 1.47
70 %
12.82 1.06***
11.09 1.33
40 %
16.68 1.64
16.82 1.93
55 %
14.76 1.19
14.50 1.36
70 %
14.17 1.02*
13.77 1.32
40 – 55 %
12.1 1.52
11.93 1.69
55 – 70 %
12.78 1.46
12.22 1.62
than ACE exercise at all intensities. WE was significantly lower (p < 0.05) in WERG compared to ACE exercise only at 70 % V˙O2 peak. Nevertheless, WE (at 40 and 55 % V˙O2 peak) and DE (at D40 – 55 % and D55 – 70 % V˙O2 peak) were similar for both modes of propulsion. The significant effect of mode of propulsion on all variables is included in Table 2.
Hintzy F et al. Muscular Efficiency During … Int J Sports Med 2002; 23: 408 – 414
Effect of power output: When comparing exercise intensities within each exercise mode, V˙O2, GE and WE were significantly affected by PO during ACE and WERG exercise, whereas NE was significantly affected by PO during WERG exercise only. V˙O2, GE (ACE: r2 = 0.37, p < 0.001; WERG r2 = 0.34, p < 0.001) and NE (WERG r2 = 0.09, p < 0.05) increased linearly with PO. WE (ACE: r2 = 0.38, p < 0.001; WERG r2 = 0.39. p < 0.001) decreased linearly with PO. Note that DE remained constant despite an increase in PO during both types of exercise. The relationships between PO and V˙O2 and between PO and mechanical efficiency indices are illustrated in the Figs. 3 and 4, respectively. Propulsion mode and power output interactions: No significant interactions were found between the propulsion mode and power output factors.
Discussion The main purpose of this study was to compare various muscular efficiency indices during ACE and WERG exercise at the same relative intensities. The choice of able-bodied subjects was purely methodological and oriented to the objective of the present study. Able-bodied subjects have fairly similar metabolic and biomechanical responses to both ACE and WERG exercise because they are equally inexperienced with these two propulsion
Fig. 4 Relationships between gross efficiency (GE), net efficiency (NE), and work efficiency (WE) and the modespecific relative intensities during arm cranking (ACE) and wheelchair (WERG) submaximal bouts.
Training & Testing
GE (%)
ACE
Fig. 3 Relationships between oxygen consumption ˙O2), and the (V mode-specific relative intensities during arm cranking (ACE) and wheelchair (WERG) submaximal bouts.
modes. Moreover, our subjects were not trained in upper body sport activities. In this respect, they formed a homogeneous group of subjects, which enabled valid ACE-WERG comparisons [23].
411 This homogeneity is very difficult to obtain in a wheelchair dependent group due to numerous disturbing methodological factors, such as injury specificity, level of physical training on upper body musculature, and the familiarity with wheelchair [2]. As a consequence, the present peak variables and efficiency values must be treated with caution for comparison with the wheelchair dependent subjects [2, 21, 23]. But previous studies have shown that the response pattern for the physiological variables was quite similar between able-bodied and wheelchair dependent subjects [5, 21, 23]. So identical trends between ACE and WERG exercise in present physiological parameter and efficiency indices could be expected if the population studied was wheelchair dependent instead of present able-bodied subjects. The V˙O2 peak, POpeak and RERpeak values attained by the present able-bodied males were similar and consistent with previous studies employing similar subjects during incremental maximal ACE [5, 9, 29] and WERG [5, 29] tests. The moderate but significant correlations found between the peak values (V˙O2peak, POpeak, RERpeak) during the two exercise modes seems to indicate in part similar individual response patterns [5, 20]. The present ACE exercise elicited significantly higher values of V˙O2 peak, POpeak, and RERpeak of approximately + 12.8 %, + 42.6 %, and + 1.6 % of those obtained during WERG exercise. The use of an identical test procedure for the two maximal tests supported the fact that the differences in peak values between ACE and WERG exercise were due only to the specificity of the propulsion mode. Similar to our findings, previous investigations found that ACE elicited
higher POpeak [5,10,13,18, 20, 30] than WERG exercise in ablebodied [5], untrained wheelchair dependent [5,18] and welltrained wheelchair dependent [10,13, 20, 30] subjects. The lower POpeak observed in WERG than in ACE exercise does support that ACE propulsion system might allow the development of a greater physical work capacity than the conventional hand-rim propulsion system used with WERG. Consequently, the comparison of muscular efficiency between these two types of propulsion must be rigorously expressed as a percentage of the individual mode-specific V˙O2peak [9]. In the present study, PO imposed for each submaximal bout (at 40, 55 and 70 % of mode-specific V˙O2peak) was significantly higher for ACE than WERG exercise (approximately + 69.0 %, + 53.3 % and + 46.2 %, respectively).
Training & Testing 412
The use of other efficiency indices, such as WE and DE, would help us to explain the ACE-WERG comparison because a nonnegligible amount of energy expenditure not contributing to the actual work accomplished is excluded from the estimates of these indices [4, 9]. As a consequence, both WE and DE values were significantly higher than GE and NE values during ACE and WERG exercise. The present values of WE and DE measured in ACE exercise were in agreement with values of two previous studies using similar subjects and similar exercise intensities [9, 32]. Concerning the present WE and DE values measured during WERG exercise, a comparison with the literature could not be made since no study, to our knowledge, has determined these efficiency indices. One of the major result of this study is the similarity between WE values (at 40 and 55 % V˙O2peak) and DE values (at D40 – 55 and D55 – 70 % V˙O2peak) during ACE and WERG
Hintzy F et al. Muscular Efficiency During … Int J Sports Med 2002; 23: 408 – 414
Values of GE and NE found in the present study are in agreement with previously reported values during ACE [9,12,16, 32] and WERG [5,16] submaximal exercise bouts in able-bodied subjects. But these values were lower than GE and NE values observed in studies using wheelchair dependent and/or wheelchair athletes during ACE [10,13, 20] and WERG [7,10,13, 24] exercise at similar intensity. Lack of skills in WERG propulsion in able-bodied subjects may have elicited more wasted energy from extra limb movements and a reduced coordination to force production [2]. Because wheelchair dependent subjects are naturally involved in upper body sport activities, some physiological adaptations could also explain the high GE and NE values observed in ACE exercise compared to able-bodied subjects [6]. In the present study, GE and NE were significantly lower in WERG compared to ACE submaximal exercise for each relative intensity. Previous studies have also showed that GE and NE were higher in ACE than WERG exercise at the same absolute intensities, in able-bodied [16], wheelchair dependent [2, 21] or wheelchair athletes [10,13, 20] subjects. As a result, the imposed exercise intensities (relative or absolute) could not explain the low GE and NE values observed in WERG compared to ACE propulsion. Previous studies have attributed the low efficiency to the biomechanical disadvantages of the hand-rim system [14,16, 20, 25] and/or to the relative small muscle mass involved during WERG propulsion [16]. The asynchronous nature of the arm cranking propulsion allowed the subject to push and pull simultaneously with controlateral arms. As a consequence, the force application was continuous during the arm cycle. In contrast, the cycle arm was divided in an active period (the pushing phase) and a passive period (the recovery phase) during hand-rim WERG propulsion. The force application is then intermittent because it does occur only during the pushing phase, i. e., the forward arm swing. As the recovery phase lasted half of the arm cycle [23], the period of the force production was then limited even when the arms were always in movement [20, 25]. An excess downward orientation of the arm forces observed in WERG propulsion may also explain in part the low GE and NE [14,16, 22]. In fact, the fraction of effective force compared to the total propulsive force was dependent on the direction of this propulsion force applied on the rims. The more the direction of the force was tangent to the rims at each position of hand-rim contact, the more this force was effective. But the hand-rim may guide the movement. i.e., push arc movement, inducing force directed too much downwards [14,16, 22]. The hand-rim system propulsion does also necessitate to hold the rims firmly in order to have sufficiently large friction between hands and rims surface [25]. As a consequence, a braking torque around the hand onto the hand-rim is often observed dur-
ing the push phase [14, 22, 25, 26]. We hypothesized that both the not-tangentially directed force, and the negative torque around the hands induced some low effective forces explaining in part our low GE and NE values during WERG compared to ACE propulsion. Recently, Vanlandewijck et al. [24] have shown that the low GE could also be explained by a significant change in the acceleration of the wheelchair propulsion during the recovery phase, caused by the arms and trunk movements. This forward arm movement can induce inertial forces to act on the wheelchair and then decrease the GE values [24]. In addition, the use of inherent neural pathways for reciprocal innervation of controlateral muscle groups has been hypothesized as a mechanism for the higher efficiency of locomotor activities that employ asynchronous limb’s movement [5]. Further, the relatively smaller skeletal muscle mass involved only for work production during WERG exercise is likely to contribute to the reduced GE and NE values compared to the ACE exercise. Indeed, WERG propulsion does require a high static work component, representing a high unmeasured work, e. g., muscular stabilization of the torso and gripping action of the hands on the rims [16, 25, 26]. During hand-rim WERG propulsion, these static efforts are able to increase the energy demand without change in external work, and so decrease the GE and/or the NE values. In summary, low GE and NE during WERG could be attributed to a greater amount of energy expenditure accounted for unmeasured work, due to the biomechanical inefficiency of hand-rim propulsion and to the additional muscular activities during WERG exercise. Results of the present study confirm this hypothesis. V˙O2unload, i. e., energy expended for internal work, was significantly higher in WERG compared to ACE exercise (8.39 vs 6.73 ml N min–1 N kg–1, respectively). For any type of propulsion, the subjects perform internal work just to move the limbs even when the external load is zero [4, 27, 31]. But during hand-rim WERG propulsion, the energy to hold the rims and to stabilize the body via isometric contraction is additionally expended during the unloaded movement. And this energy expenditure does not lead to the generation of external forces. In the present study, it could be concluded that the hand-rim WERG propulsion induced higher internal work than simultaneous ACE propulsion, i. e., higher inertial energy losses. It must be noted that both unloaded ACE and WERG conditions could not be precisely verified in the present study. The V˙O2unload values must then be cautiously discussed when compared to the literature, especially with studies using complex biomechanical model for internal work determination [27, 31].
Hintzy F et al. Muscular Efficiency During … Int J Sports Med 2002; 23: 408 – 414
The present study also confirmed that PO markedly affects the efficiency indices during both modes of propulsion. As previously observed [5,12], an increase in GE (within each mode of propulsion) and NE (only with WERG) with increments in PO was found in the present study over the range of exercise intensity studied. Kang et al. [9] and Powers et al. [12] explained the GEPO and NE-PO relationships by the decreasing effect of the unmeasured work that comprises the total energy expenditure. In contrast to GE and NE, WE decreased and DE remained unchanged with an increase in PO for the range of exercise intensity investigated in both ACE and WERG exercise. Similar decreases in WE have been found by previous studies during cycling [5] and ACE [12] exercise. Assuming that the total mechanical PO is the sum of internal and external work rate, internal work rate represents a reduced proportion of the total mechanical PO as the external work rate increases and so WE may decrease with PO [5,12]. This study supports the hypothesis that the same general trend in efficiency indices as a function of PO could be obtained during alternative propulsion (e. g., leg cycling or ACE exercise) and simultaneous propulsion (e. g., hand-rim WERG exercise). According to Kang et al. [9], failure to find an influence of the PO on NE (during ACE condition) or DE (during ACE and WERG condition) in the present study could partly be explained by the low range of PO investigated and by the low number of dots per regression. Finally, the magnitude of the difference between GE and WE indices decreased with the PO within each mode of propulsion. When external mechanical work rate increases, the relative contribution of the internal work to the total energy expenditure in WE calculation will diminish as it becomes proportionally less [31]. As a consequence, comparison of physiological responses between two modes of propulsion requires the use of efficiency indices different from GE and NE, especially when PO is low [27]. In summary, GE and NE were lower during WERG compared to ACE exercise whereas WE and DE were similar, at the same relative intensities. By studying differences in values of muscular efficiency indices, insight may be obtained into mechanism that causes WERG propulsion to be energy-wasteful. Based upon the present findings, it is possible that the muscular efficiency differences in the ACE-WERG comparison could be mainly attributable to a higher internal work in WERG than in ACE exercise due to the specific hand-rim pattern propulsion in WERG.
References 1
McArdle WD, Katch FI, Katch VL. Exercise Physiology. Energy, Nutrition, and Human Performance. Philadelphia: Lea and Febiger, 1981: 101 2 Brown DD, Knowlton RG, Hamill J, Schneider TL, Hetzler RK. Physiological and biomechanical differences between wheelchair-dependent and able-bodied subjects during wheelchair ergometry. Eur J Appl Physiol 1990; 60: 179 – 182 3 Devillards X, Calmels P, Sauvignet B, Belli A, Denis C, Simard C, Gautheron V. Validation of a new ergometer adapted to all types of manual wheelchairs. Eur J Appl Physiol 2001; 85: 479 – 485 4 Gaesser GA, Brooks GA. Muscular efficiency during steady-rate exercise: effects of speed and work rate. J Appl Physiol 1975; 38: 1132 – 1139 5 Glaser RM, Sawka MN, Brune MF, Wilde SW. Physiological responses to maximal effort wheelchair and arm crank ergometry. J Appl Physiol 1980; 48: 1060 – 1064 6 Glaser RM, Sawka MN, Laubach LL, Suryaprasad A. Metabolic and cardiopulmonary responses to wheelchair and bicycle ergometry. J Appl Physiol 1979; 46: 1066 – 1070 7 Goosey VL, Campbell IG, Fowler NE. Effect of push frequency on the economy of wheelchair racers. Med Sci Sports Exerc 2000; 32: 174 – 181 8 Jones D, Baldini F, Cooper RA, Robertson R, Widman L. Economical aspects of wheelchair propulsion. Med Sci Sports Exerc 1992; 24: S32 9 Kang J, Robertson RJ, Goss FL, Dasilva SG, Suminski RR, Utter AC, Zoeller RF, Metz KF. Metabolic efficiency during arm and leg exercise at the same relative intensities. Med Sci Sports Exerc 1997; 29: 377 – 382 10 Martel G, Noreau L, Jobin J. Physiological responses to maximal exercise on arm cranking and wheelchair ergometer with paraplegics. Paraplegia 1991; 29: 447 – 456 11 Mukherjee G, Samanta A. Physiological response to the ambulatory performance of hand-rim and arm-crank propulsion systems. J Rehab Res Dev 2001; 38: 391 – 399 12 Powers SK, Beadle RE, Mangum M. Exercise efficiency during arm ergometry: effects of speed and work rate. J Appl Physiol 1984; 56: 495 – 499 13 Price MJ, Campbell IG. Thermoregulatory and physiological responses of wheelchair athletes to prolonged arm crank and wheelchair exercise. Int J Sports Med 1999; 20: 457 – 463 14 Roeleveld K, Lute E, Veeger D, Gwinn T, Van der Woude L. Power output and technique of wheelchair athletes. Adapt Phys Act Quart 1994; 11: 71 – 85 15 Sawka M. Physiology of upper body exercise. Exerc Sports Sci Rev 1986; 14: 175 – 212 16 Sawka MN, Glaser RM, Wilde SW, von Luhrte TC. Metabolic and circulatory responses to wheelchair and arm crank exercise. J Appl Physiol 1980; 49: 784 – 788 17 Shephard RJ, Allen C, Benade AJS, Davies CTM, Di Prampero PE, Hedman R, Marriman JE, Myhre K, Simmons R. The maximum oxygen intake. An international reference standard of cardiorespiratoy fitness. Bull WHO 1968; 38: 757 – 764 18 Simard C, Noreau L, Par G, Pomerleau P. Maximal physiological response during exertion in quadriplegic subjects. Can J Appl Physiol 1993; 18: 163 – 174 19 Toner MM, Sawka MN, Levine L, Pandolf KB. Cardiorespiratory responses to exercise distributed between the upper and lower body. J Appl Physiol 1983; 54: 1403 – 1407 20 Tropp H, Samulsson K, Jorfeldt L. Power output for wheelchair driving on a treadmill compared with arm crank ergometry. Br J Sports Med 1997; 31: 41 – 44 21 Van der Woude LHV, DeGroot G, Hollander AP, Schenau GJV, Rosendal RH. Wheelchair ergonomics and physiological testing of prototypes. Ergonomics 1986; 29: 1561 – 1573 22 Van der Woude LHV, Veeger HEJ, De Boer Y, Rozendal RH. Physiological evaluation of a newly designed lever mechanism for wheelchairs. J Med Eng Tech 1993; 17: 232 – 240 23 Van der Woude LHV, Veeger HEJ, Rozendal RE, Sargeant AJ. Optimum cycle frequencies in hand-rim wheelchair propulsion. Wheelchair propulsion technique. Eur J Appl Physiol 1989; 58: 625 – 632 24 Vanlandewijck YC, Spaepen AJ, Lysens RJ. Wheelchair propulsion efficiency: movement pattern adaptations to speed changes. Med Sci Sports Exerc 1994; 26: 1373 – 1381
Training & Testing
exercise. To our knowledge, direct comparisons between ACE and WERG exercise in WE and DE indices have never been reported in the literature. As suggested before, the pattern of the hand-rim propulsion then induced higher energy losses than the pattern of the ACE propulsion during unloaded exercise. But when a large amount of unmeasured work (V˙O2unload) was excluded from the total energy expenditure, WERG becomes a propulsion system as efficient as ACE movement at the same relative exercise intensity. However, at 70 % V˙O2peak, WE was significantly higher in ACE than WERG exercise. In fact, V˙O2unload represented a smaller percentage of the total energy expenditure at high (70 % V˙O2peak) compared to low (40 % V˙O2peak) intensities. The influence of the unmeasured work being more important at relatively low rather than high intensities [27], WE becomes higher in ACE than WERG during exercise at 70 % V˙O2peak.
413
25
Veeger HEJ. Biomechanics of manual wheelchair propulsion. In: Van der Woude LHV, Meijs PJM, Van der Gurtes BA, de Boes YA (eds). Ergonomics of Manual Wheelchair Propulsion, State of the Art. Milano: Edizioni pro juventute, IOS, 1991: 201 – 203 26 Veeger HEJ, Van der Woude LHV, Rosendal RH. Effect of hand-rim velocity on mechanical efficiency in wheelchair propulsion. Med Sci Sports Exerc 1992; 24: 100 – 107 27 Wells R, Morrissey M, Hughson R. Internal work and physiological responses during concentric and eccentric cycle ergometry. Eur J Appl Physiol 1986; 55: 295 – 301 28 Whipp BJ, Wasserman K. Efficiency of muscular work. J Appl Physiol 1969; 26: 644 – 648
29
Wicks JR, Lymbuerner K, Dinsdale SM, Jones NL. The use of multistage exercise testing with wheelchair ergometry and arm cranking in subjects with spinal cord lesions. Paraplegia 1977 – 1978; 15: 252 – 261 30 Wicks JR, Oldridge NB, Cameron BJ, Jones NL. Arm cranking and wheelchair ergometry in elite spinal cord-injured athletes. Med Sci Sports Exerc 1983; 15: 224 – 231 31 Widrick JJ, Freedson PS, Hamill J. Effect of internal work on the calculation of optimal pedalling rates. Med Sci Sports Exerc 1992; 24: 376 – 382 32 Yamasaki M, Irizawa M, Ishii K, Komura T. Work efficiency of paraplegia during arm cranking. Ann Physiol Anthrop 1993; 12: 79 – 82
Training & Testing 414
Hintzy F et al. Muscular Efficiency During … Int J Sports Med 2002; 23: 408 – 414
