Despite significant advances in mountain bike suspension systems in recent years, little is known about the effects of these systems on rider performance. Furthermore, the effects of these suspension systems on rider performance under field conditions have, to our knowledge, only received limited investigation (2,9).
The majority of mountain bikes produced at present are equipped with either a front suspension (FS) or a front and rear (dual) suspension (DS) system, the latter purported to increase rider comfort, control, and possibly performance, perhaps by reducing physical trauma due to excessive vibration. Although the benefits of a DS design may seem obvious, the potential disadvantages from the standpoint of metabolic cost to the rider have not been fully examined. The loss of pedaling energy due to compression of the suspension system followed by spring dampening has the potential to result in greater energy expenditure compared with a front-only suspension system.
In a competitive cycling setting, rider performance is best determined by time to completion of a set course. Although this is the final and most direct measurement of a cyclist’s athletic ability, other parameters such as oxygen consumption and power output can also be utilized to assess differences in bike design, all else being equal. One recent study reported no difference in energy expenditure between cyclists riding front and dual suspension equipped bicycles (9).
Due to the fact that approximately 70% or more of race time on North American mountain bike cross-country courses is spent climbing (U.S. Cycling, personal communication), we were particularly interested in determining the metabolic and physiological responses during uphill mountain-bike cycling. Thus, the objective of this study was to assess the effects of FS versus DS systems on oxygen consumption, power output, and other physiological variables during uphill cycling on a paved- and off-road course.
Six male sub-elite mountain-bike cyclists (see Table 1) were informed of the experimental procedures and signed a letter of consent before participation in the study. This project was approved by the Institutional Review Board of Pepperdine University.
Subjects reported to the laboratory in the morning for body composition assessment, aerobic cycling performance (O2peak, Wpeak), and anaerobic cycling performance (30-s Wingate test). Subjects were asked to refrain from any intense training in the 48 h before testing but were allowed to perform their usual daily exercise/activity patterns. Body composition was determined via skin-fold thickness assessment (3). The subjects then underwent a progressive incremental cycling test (100 W for 1 min, then 25 W·min−1) to exhaustion on an electrically braked cycle ergometer (Monark 829E, Varberg, Sweden). O2peak was determined by directing expired air to a MedGraphics CardioO2 system (Medical Graphics, St. Paul, MN) calibrated before each test with commercially prepared gas mixtures. Heart rates were recorded at 1-min intervals during the incremental test (Polar Vantage XL, Stamford, CT). Peak power output on the incremental cycling test was calculated as described by Kuipers et al. (5).
We determined, before this study, that neither O2peak nor measures of power on the Wingate cycling test (peak, mean, or end power) were different, if either the O2peak or Wingate test preceded each other, separated by a 45-min rest interval. Accordingly, 45 min after the O2peak test, subjects performed a 30-s Wingate cycling test on a friction-braked cycle ergometer (Monark 814E, Varberg, Sweden) for determination of peak anaerobic power (WpeakWin). This ergometer was configured with an optical sensor interfaced with a personal computer with software for data collection (Sports Medicine Industries, St. Cloud, MN). WpeakWin was determined by averaging the first 5 s of data of the 30-s test.
Mountain bike suspension systems.
Both the front-suspension (FS) and dual suspension (DS) bicycles (size 46 cm) were equipped with the same shifting and drive train components, front-suspension systems (Rock Shox Indy Fork; Rock Shox, San Jose, CA), and wheels with tires inflated to similar pressures. The DS bicycle employed a four-bar linkage rear-suspension with a Rock Shox Deluxe rear-shock absorber. Both bicycles were instrumented with mountain bike versions of the SRM Training System (Schoberer Rad Messtechnik, Welldorf, Germany). This system consists of a Powermeter, which has several strain gauges mounted within a deformable disk positioned between the crank arm (175-mm length) and the chain ring, linked to a Powercontrol unit (a small handlebar mounted computer) which records and stores power, speed, cadence, distance, and HR data. A recent study compared power measured with an SRM system with that of the power delivered to a Monark ergometer flywheel (6). That study concluded that the power measured on an SRM system was valid and accurate, and differed from the power delivered to the ergometer flywheel only by an amount lost to chain friction (2.36% or 2–7 W).
Each subject was given an orientation to the on-road asphalt course (ASP) and off-road course (OFF) by visual inspection before performing the uphill cycling trials. Again, as with the laboratory tests, subjects were asked to refrain from intense training in the 48 h preceding the uphill time trials but were permitted to perform their usual daily exercise/activity patterns. For each course, the subjects completed in random order a time trial on the FS or DS bicycle, with each time trial separated by a 45-min recovery period. This 45-min recovery period would have allowed adequate rest before the next uphill time trial. Each time trial represented less than 10% of the time the cyclist would typically spend climbing in a race, and the 45-min recovery period also allowed HR to return to preexercise resting levels. The ASP tests were conducted 1 wk after the laboratory tests, and the OFF tests 1 wk after the ASP tests. The ASP course was 1.62 km in length with an elevation gain of 183 m (14.2% grade), the OFF course 1.38 km long with an elevation gain of 123 m (11.3% grade). The fire access road utilized for the off-road trials had no technically difficult sections that might have altered the subjects ability to ride at a time-trial pace but was rocky and rutted as a result of winter rains.
Expired air was collected during the uphill cycling trials using an Aerosport KB1-C metabolic system (Aerosport, Ann Arbor, MI) calibrated with commercially prepared gas mixtures before each trial. This portable metabolic system consists of an analyzer module with a HR receiver integrated into the module, a three-position variable flow pneumotach, and a harness for carrying the 1.2 kg unit on a subject. A 180-line internal memory buffer that can store up to 3 h of data from one continual test permits retrieval of data after a test. The KB1-C system uses the same gas analyzers and variable flow pneumotach as the Aerosport TEEM 100 portable metabolic system. The TEEM 100 (7,10) and KB1-C (4) provide valid and reliable measures of O2 during incremental and steady-state exercise. We determined in pilot testing that the medium-flow setting on the pneumotach (10–120 L·min−1) would encompass the range of expected ventilation rates. Subjects wore a Hans Rudolph face mask (8930 Series, Kansas City, MO) with the pneumotach attached (for comfort, rather than a mouthpiece), and expired gas collection was averaged every 20 s. The SRM Powermeters were calibrated before each trial according to the manufacturer’s specifications, and data collection (for power, speed, cadence, HR) was averaged every second during each trial. Each subject was fitted with a chest belt and transmitter for transmission of HR to the SRM Powercontrol and KB1-C metabolic unit (Polar, Stamford, CT).
The subjects were given a 10-min warm-up on the bicycle to be tested before each uphill time trial. The subjects were instructed to ride the uphill courses as fast as possible at an intensity approximating typical race conditions. The face mask for expired gas collection was then adjusted on the subjects face, and, after 1 min of pre-time-trial data collection, the Powercontrol timer was activated, and the subject rode the uphill course. Metabolic and SRM system data collection was terminated at the “finish line” of each trial. Ride duration was timed by the SRM system and confirmed by a handheld stopwatch. A capillary blood sample (150–200 μL) from a finger was taken before and at 2 min after completion of each uphill cycling trial for determination of whole blood lactate concentration. Blood samples were stored in microtainer tubes containing EDTA (Becton Dickinson, Franklin Lakes, NJ) on ice for later analysis (YSI 2300 StatPlus, YSI Incorporated, Yellow Springs, OH). These blood samples were analyzed within 3 h after collection. After each time trial, metabolic data from the KB1-C unit, and SRM data from the Powercontrol, were downloaded to a portable PC for later analysis.
Because the uphill cycling trials of several subjects resulted in partial completion of a full min at the end of their trials, trials for each suspension system were analyzed for 10 min on the ASP and 8 min on the OFF course. A one-way ANOVA was used to compare mean differences between FS and DS. Dependent variables included O2, heart rate, power output, pedaling cadence, and velocity, all of which were analyzed using the average of 10-min and 8-min data collection periods for the FS and DS trials, respectively. In addition, total ride time for the FS versus DS was analyzed for mean differences. Separate ANOVAs were conducted for the ASP and OFF courses.
A two-way ANOVA (time × suspension system) was employed to determine whether there were minute-by-minute differences in O2, HR, power output, cadence, and velocity between the FS and DS bicycles. When significant interactions were found, these were further investigated using a Scheffe post hoc test for multiple comparisons. A P-value of 0.05 was accepted as the level of statistical significance for all analyses.
When subjects rode the ASP course, total ride time, average minute-by-minute heart rate, and peak blood lactate were similar (P > 0.05) during the FS trial and the DS trial (Table 2). Similarly, when subjects rode the OFF course, total ride time, average minute-by-minute heart rate, and peak blood lactate were not significantly different during the FS trial versus the DS trial (Table 2). The average oxygen cost, when expressed in absolute values (L·min−1), relative to body mass (mL·kg−1·min−1), or relative to mass of the cyclist plus mass of the bicycle (mL·[kg body wt + kg bike wt]−1 ·min−1), was not different (P > 0.05) between the two suspension systems during either the ASP or OFF course rides (Table 2). Furthermore, when the O2 values were averaged for each minute of either the ASP or OFF course, this finding persisted. O2 (mL·[kg body wt + kg bike wt]−1·min−1) increased rapidly between minute 1 and minute 2 of the uphill trials, and then remained unchanged (P > 0.05) until the completion of each time trial (Fig. 1). Heart rate rose progressively throughout each time trial but, when compared on a minute-by-minute basis for either the ASP or OFF course, was not different (P > 0.05) between suspension type (Fig. 2).
Power outputs, determined from the SRM Powermeter, were different on the FS compared with the DS bicycle when measured on either the ASP or OFF course. Average absolute (W) and relative (W·[kg body wt + kg bike wt]−1·min−1) power for each course condition were significantly lower on the FS compared with the DS bicycle (Table 2, P < 0.001). When absolute power outputs were compared on a minute-by-minute basis, this finding persisted. Power outputs on-road and off-road were significantly lower (P < 0.001) for the FS compared with the DS bicycle at all time points (Fig. 3). Mean cadence and speed were not different between suspension systems when averaged for each road condition (Table 2), and this finding persisted when the minute-by minute data were analyzed (data not shown).
The major finding of this study was that cardiovascular performance was similar both on- and off-road on front and dual suspension bicycles, but that power output was significantly higher on the dual suspension bicycle during the uphill cycling trials. Furthermore, bicycle type did not affect time to complete each trial, oxygen cost, or heart rate response of the cyclists. The cyclists performed the uphill trials at ∼84% of O2peak and ∼92% of HRmax irrespective of road condition or bicycle type, ∼69% and ∼88% of O2peak power output (PPO), and ∼30% and ∼38% of Wingate peak power output on the front and dual suspension bicycles, respectively. Wilber et al. (11), in laboratory exercise testing, determined that elite male off road cyclists’ lactate threshold performance corresponded to 77% O2max, 64% PPO, and 86% HRmax. The subjects in our study were sub-elite but performed the uphill cycling trials at higher relative intensities than the elite cyclists studied by Wilber et al. Whether elite cyclists perform at higher relative intensities (% O2max, %PPO, %HRmax) under field conditions is yet to be determined.
We expected that not only the larger mass of the dual suspension bicycle but also the energy cost of compressing the rear suspension during pedaling would result in a higher O2. However, the metabolic cost (O2) of riding the different suspension types was not different, even when we accounted for the differences in mass between the bicycles (Table 2). Our data extend the findings of Seifert et al. (9). They found no differences in oxygen cost of riding a front and dual suspension bicycle on a flat looped course with manufactured bumps. Unfortunately, that study, which also included an uphill time trial, provided no data as to the oxygen cost or power output of riding the different suspension system bicycles uphill.
The power output differences between the front and dual suspension bicycles, without concomitant cardiovascular response differences, were surprising. We expected that the O2 data would track the power output data or, at minimum, that the O2 responses would follow the power output trends. Steady metabolic rates (O2 based) were attained by the second minute of each cycling trial and remained unchanged until the completion of each trial (Fig. 1). The power output data presented in Figure 3 shows substantial power fluctuations during the cycling trials, and the nonsmoothed data (not averaged) were also highly variable within each minute. Furthermore, the average power output at each time interval was approximately 80 W·min−1 lower on the front compared with dual suspension bicycle. This power output should have resulted in a ∼1 L·min−1 or ∼13 mL·kg−1·min−1 lower metabolic rate for the front suspension bicycle (1).
In laboratory ergometry, O2 and HR respond linearly to changes in power output. In a study of road cycling time-trial performance, heart rates were similar during a 150 min paced ride followed by a 20-km time trial, but power output was significantly higher during the time trial (8). Our study of mountain-bike cycling showed a similar dissociation between power output and heart rate (Fig. 2) and additionally, dissociation between power output and O2 (Fig. 1). Thus, the usual relationship between power output, cardiovascular, and metabolic responses observed in a laboratory setting appears to change when cyclist’s perform in the field. This observation may impact the design of exercise training programs based on laboratory testing and deserves further investigation.
Although the mean cycling velocities and time to complete the time trials were similar on both bicycles (Table 2), we believe that the higher power outputs required to pedal the dual suspension bicycle uphill were generated to overcome the compression of the rear-suspension. It is possible that the rear suspension spring absorbed some of the torque energy being applied to the pedals, resulting in higher torques having to be applied to the drive train in order to maintain uphill speed. The practical issue raised by this finding is whether a dual suspension bicycle can be used effectively in cross-country racing where around 70% or more of the time spent racing involves uphill riding (U.S. Cycling, personal communication). The power output data (Fig. 3) suggest that the energy cost of generating ∼80 W·min−1 more power on a dual suspension bicycle may affect cross-country racing performance. If this power output difference remained constant over the course of a 2-h race, then the expected extra energy expended would amount to around 69,550 kJ. This energy cost is well in excess of, for example, the stored energy available from glycogen in skeletal muscle (1) and is therefore a physiological impossibility during the hypothetical 2-h race. Thus, we interpret the differences in power output, between the front and dual suspension bicycles, to energy being conserved in the bicycle suspension/frame being retransmitted back into the bicycle/rider. Although the cyclists’ had to generate a higher power output to cycle uphill on the dual suspension bicycle, that power was likely conserved by the rear-suspension spring and, during rebound of the spring after compression, contributed to the forward momentum of the bicycle. This interpretation requires further investigation. More to the point, the metabolic and heart rate data (Figs. 1 and 2) show no difference in energy cost between riding a front and dual suspension bicycle on either an ASP or OFF uphill course.
We are confident that the measured variables in this study are valid. The subjects used in this study had all been riding mountain bikes for at least 5 yr and were well acclimatized to the extended climbing required by mountain biking in Southern California. The similarities in times to complete each ride, heart rate data, and blood lactate data suggest that intensities of effort by the cyclists’ were similar. We measured peak blood [La] only as a marker of intensity of effort. These values were similar in each cycling trial (Table 2) and were also similar for the different road conditions. Furthermore, heart rate responses, which are usually used to quantify intensity of effort, were similar irrespective of bicycle type during the uphill cycling trials (Fig. 2).
In conclusion, this investigation was restricted to a particular dual suspension design (four-bar linkage rear suspension system), and therefore these findings cannot be extended to other suspension systems. Despite significant differences in power output between the front and dual suspension systems during uphill cycling, these differences did not translate into significant differences in oxygen cost or time to complete the uphill courses. We suggest that the bicycle suspension systems used in this study will result in similar performances during race conditions, particularly racing that requires extensive climbing. Furthermore, it is possible that a dual suspension bike might provide a greater advantage versus a front suspension bike during downhill riding, thereby resulting in faster race times over a cross-country race. Whether a dual suspension mountain bike can be raced competitively and at a similar energy cost to a front suspension only bicycle in a mountain bike cross-country race is yet to be determined.
The authors would like to thank Marian Murray and Galen Okazaki for their assistance with making the field data collection possible. The authors also thank Specialized Bicycle Company for the use of the two bicycles tested in this study, and Dean Golich for the use of an SRM Powermeter. The results of this investigation do not constitute endorsement by the authors or ACSM of the SRM training system or bicycles used in the study.
1. Brooks, G. A., T. D. Fahey, and T. P. White. Exercise Physiology, Human Bioenergetics, and Its Applications, 2nd Ed. Mountain View, CA: Mayfield Publishing Co., 1996, pp. 30, 581.
2. Demchak, T. J., and J. K. Linderman. Ultraendurance cycling: a field study of human performance during a 12 hour mountain bike race. Med. Sci. Sports Exerc. 31(Suppl. 5):S107, 1999.
3. Jackson, A. S., and M. L. Pollock. Generalized equations for predicting body density of men. Br. J. Nutr. 40:497–504, 1978.
4. King, G. A., J. E. McLaughlin, E. T. Howley, D. R. Bassett, and B. E. Ainsworth. Validation of Aerosport KB1-C portable metabolic system. Med. Sci. Sports Exerc. 31 (5):S285, 1999.
5. Kuipers, H., F. T. J. Verstappen, H. A. Keizer, P. Guerten, and G. Van Kraneburg. Variability of aerobic performance in the laboratory and its physiological correlates. Int. J. Sports Med. 6:197–201, 1985.
6. Martin, J. C., D. L. Milliken, J. E. Cobb, K. L. McFadden, and A. R. Coggan. Validation of a mathematical model for road cycling power. J. Appl. Biomech. 14:276–291, 1998.
7. Novitsky, S., B. Chatr-Aryamontri, D. Guvakov, and V. L. Katch. Validity of a new portable indirect calorimeter: the Aerosport TEEM 100. Eur. J. Appl. Physiol. 70:462–467, 1995.
8. Palmer, G. S., T. D. Noakes, and J. A. Hawley Effects of steady-state versus stochastic exercise on subsequent cycling performance. Med. Sci. Sports Exerc. 29:684–687, 1997.
9. Seifert, J. G., M. J. Luetkemeier, M. K. Spencer, D. Miller, and E. R. Burke. The effects of mountain bike suspension systems on energy expenditure, physical exertion, and time trial
performance during mountain bicycling. Int. J. Sports Med. 18:197–200, 1997.
10. Wideman, L., N. M. Stoudemire, K. A. Pass, C. L. McGinnes, G. A. Gaesser, and A. Weltman. Assessment of the Aerosport TEEM 100 portable metabolic measurement system. Med. Sci. Sports. Exerc. 28:509–515, 1996.
11. Wilber, R. L., K. M. Zawadzki, J. T. Kearney, M. P. Shannon, and D. Disalvo. Physiological profiles of elite off-road
and road cyclists. Med. Sci. Sports Exerc. 29:1090–1094, 1997.