Despite the reported popularity of Bicycle Motocross (BMX), research surrounding the physiological demands of this cycling discipline remains limited. Recently, however, researchers have started to take a greater interest in this esoteric activity (6,7,13,14). A large proportion of this research has concentrated on the contribution of the lower limbs on velocity production (i.e., power, torque, rate of force production) (8,16). There is, to date, however, a shortage of studies that have investigated the effect of the upper body on velocity production in BMX cycling (1,17). This is in contrast with other cycling disciplines, where upper-body muscle activation has been captured using surface electromyography (sEMG) (2,10,11,15). For instance, Hurst et al. (2016) analyzed the possible fatigue effect of wheel size on the upper body in cross county mountain bikers. Hurst et al. (2016) reported no significant difference in the upper-body muscle activation between riders who rode with 3 different wheel sizes, thus rejecting the hypothesis that larger wheels reduce muscle activity and as a result reduce fatigue. To date, no study has analyzed performance in BMX cycling using an sEMG, and only 2 studies have examined the contribution of the upper body on performance.
For example, Bertucci et al. (2005) analyzed the effect of the upper body on performance in BMX cycling. The study of Bertucci et al. showed that 32% higher force was applied to the bicycle during standing sprints, compared with seated sprints. Similar findings were reported in a study that compared laboratory sprints on a cycle ergometer to sprints performed on a BMX track when riders used their own bikes (17). Rylands et al. (2015) concluded that the laboratory cycle ergometer restricted the natural lateral oscillation of the bicycle and resulted in a mean reduction in power of 34%. Both these studies confirmed that the oscillation of a BMX bicycle is only possible when a rider is pedaling, as the movement is used as leverage by the upper body (1,17).
However, these oscillation movements are not the only upper-body contributions reported to have an impact on BMX cycling. Cowell et al. (3) performed a skill and movement analysis on 6 male BMX riders. The authors reported that during a BMX race, 31% (9.64 seconds) of the race was spent pedaling, with 6.6% of the time spent pedaling down the start ramp (2.62 seconds) in which upper-body oscillation occurs. Cowell et al. (3) also noted other contributions of the upper-body movement, and commented that during a BMX race 44% of the time (17 seconds) was spent pumping.
Pumping is a term used to describe a technique performed by a BMX rider on the rhythm section of a BMX track during the race. The technique of pumping has been reported by competitive riders as a “natural movement” or in academic terms an autonomous motor function (5,12,20). The rhythm section of the track where the technique is performed encompasses a straight section with a number of rolling mounds/hills (Figure 1). The technique requires the rider to push down the front wheel of the bike at the top of a hill, to maintain maximum velocity during the rhythm section.
If indeed 44% of the total time of a BMX race is spent pumping, it could be hypothesized that the pumping technique is an important factor in the race. Based on such considerations, the aim of this study, therefore, was to analyze the effect of pumping on the production of velocity while riding on a BMX track.
Experimental Approach to the Problem
The subjects were tested twice in a single day with 30 minutes rest between trials. Each of the riders was competent at performing the pumping technique and had the opportunity to familiarize themselves with the nonpumping technique. The trials were all performed on a purpose-built indoor BMX track at the National Cycling Centre in Manchester (United Kingdom). All the riders were in the competition phase of their season but had not raced for a minimum of 3 days before the test. Each rider ensured they had eaten a minimum of 1 hour before the test and consumed fluids throughout the day to maintain hydration.
Ten national standard BMX cyclist (mean age, 23 ± 3 years; body mass, 71 ± 3 kg and 175 ± 7 cm) participated in the study. All riders had competed at a national and an international level for a minimum of 8 years, and had race experience on the track used for testing (National Cycling Centre BMX Track, Manchester, United Kingdom).
A detailed description of the test protocol was issued to all riders and written and informed consent was obtained from each participant before the study. The riders were informed of the benefits and risks of the investigation before signing the consent form. The research project received ethical approval from the University of Derby Ethics Human Studies Board and the study was conducted according to the recommendations of the Declaration of Helsinki.
To establish if the upper-body activity significantly affected velocity production, 2 separate randomized trials were performed on the indoor BMX track. The indoor track had a 5-m high start ramp with a 28° decent. The track measured 400 m in length, comprised 4 straights, with a number of technical jumps on each straight section, and 3 berms (corners). The order of the trials were randomized and conducted on the same day.
The riders performed a structured warm-up consisting of three 10-second sprints from a 5-m high start ramp using a standard electronic start gate (Pro-Gate, Rockford, IL, USA). Following the randomized ordering of the trials, the riders completed a full lap of the track using a pumping technique or nonpumping for 2 separate. A 30-minute rest period was provided between the trials to avoid fatigue. Both trails were recorded using a HD Camera (Panasonic HC-X900) with shutter speed of 1/8000th of a second. This device was also used to record the lap times.
A sEMG was used to establish any variation in muscle activation between the trials.
The sEMG data were recorded on the rhythm section of the BMX track. The sEMG was used at the biceps brachii, triceps brachii, vastus lateralis, and medial gastrocnemius. To record the sEMG, a wireless mobile EMG system was also used (Delsys Trigno; Delsys, Massachusetts, USA), with data recorded at 1926 Hz.
The sEMG sensors used 2 parallel bars at 1 cm spacing to reduce cross talk between muscles (9) and were positioned following preparation of the muscles. This involved shaving the area of sensor placement, lightly abrading and then cleaning with alcohol wipes to minimize skin impedance. The sensors were all fitted medially to the left side of the rider's body running parallel to the muscle fibers. Placement of the sensors was in accordance with the Surface EMG for Non-Invasive Assessment of Muscles project, SENIAM (18) recommendations. The sensors were held in place using elasticated bandages.
After data collection, the sEMG data were full-wave rectified and then filtered at 20 Hz using a second-order low-pass Butterworth filter. Normalization of data followed the method of Sinclair et al. (2012). Sinclair et al. (2012) conducted a field study examining sEMG in running and stated that the environment did not allow the researchers to normalize the sEMG signal to a maximal voluntary isometric contraction. The rationale being that the action of running involves dynamic muscular activity. As a result, Sinclair et al. (2012) proposed that sEMG data should be normalized to a dynamic peak task (DPT), that being the peak amplitude observed during the field-based trials. As BMX cycling also involves dynamic muscle activity, this protocol was incorporated into this study. The peak amplitude recorded during the 2 trials was used as the DPT and all sEMG data are presented as a percentage of the DPT. Data were not captured from 2 of the riders because of unknown reasons. Therefore, sEMG data were analyzed for the 8 complete data sets recorded, while all 10 lap times of the riders were used for analysis of differences between techniques.
The independent variables in the analyses were pumping and nonpumping techniques. The dependent variables were lap time, upper-body muscle activation, and lower-body muscle activation. Normality of data was first confirmed using a Shapiro-Wilk test. Differences in muscle activity were first determined between pumping and nonpumping techniques using paired sampled t-tests. To determine any statistical differences within muscle groups, and to establish whether muscle recruitment differed by technique, data were subjected to a within-groups repeated measures analysis of variance. Differences were observed where significant, Bonferroni pairwise comparisons were used to determine where the differences occurred, and to control for type I errors. Effect sizes were determined using partial Eta2 (η2). Partial η2 were interpreted based on their magnitude, where a value between 0.0 and 0.1 indicates a small effect; 0.1–0.3, medium effect; 0.3–0.5, moderate effect; and >0.5, large effect (19). Data are presented as mean ± standard deviation unless stated otherwise. All statistical analyses were conducted using SPSS 21.0 (SPSS Inc., Chicago, IL, USA).
The results showed a significant difference existed between the riders' lap times when performing the pumping technique compared with nonpumping (F1,9 = 143.457; p = 0.001; η2 = 0.941). The mean percentage time difference between pumping and nonpumping was 19.50 ± 4.25% (34.7 ± 1.49 seconds and 43.3 ± 3.1 seconds, respectively).
A significant difference (F1,9 = 2643.882; p = 0.001; η2 = 0.997) was also found between the velocity in the pumping and nonpumping trials, with riders mean velocity in the pumping trail (42 ± 1.8 km·h−1) being 21.81 ± 5.31% greater than the nonpumping (33 ± 2.9 km·h−1) trial.
The sEMG results revealed no significant differences when comparing muscle activity between pumping with nonpumping for each muscle group; biceps brachii, t(7) = 0.319, p = 0.76; triceps brachii, t(7) = 0.730, p = 0.49; vastus lateralis, t(7) = 0.398, p = 0.702; and gastrocnemius t(7) = -0.492, p = 0.64. Furthermore, no significant differences were found between muscle groups when comparing muscle activation within the pumping technique (F3,32 = 0.797; p = 0.51; η2 = 0.08) and within the nonpumping technique (F3,32 = 0.833; p = 0.49; η2 = 0.08).
The difference in percentage of DPT compared with the pumping and nonpumping trials was also not statistically significant (t = 0.306, p = 0.76). Despite the lack of statistically significant differences between muscle activity for pumping and nonpumping, the mean percentage differences were 9.12% (biceps brachii), 11.85% (triceps brachii), 10.98% (vastus lateralis), and 11.42% (medial gastrocnemius).
The purpose of this research study was to: (a) Ascertain if upper-body activation had a significant impact on velocity production in BMX cycling and (b) To quantify the level of contribution made by pumping if an impact was found.
The major finding from this study was that the upper body did have a significant impact on velocity production (p = 0.001), with the mean velocity in the pumping trial being 21.81 ± 5.31% greater than the nonpumping trial. Based on this result, the technique of pumping can be considered to be an important contributing factor toward velocity production in BMX cycling. The mean results from the study found that the riders using the pumping technique (34.7 ± 1.49 seconds) completed a lap 19.50 ± 4.25% faster compared with the nonpumping (43.3 ± 3.1 seconds) lap. Although the results from the current study show that the technique of pumping is a significant factor in BMX cycling, the degree to which this has an impact could still be somewhat understated. For example, analysis of the video recordings revealed that the riders were performing both the pumping and nonpumping techniques in the respective trials. All the riders in the study were competent at pumping; however, several of the riders did find the implementation of the nonpumping technique challenging. This may be due to the technique of pumping being an autonomous motor function. If, as visually noted, the riders did not subconsciously commit to the nonpumping technique, the variation in the 2 trials could have been even greater. This supposition is supported by Cowell et al. (3) who analyzed the time spent performing a number of skills and movement patterns in 26 elite male riders at the 2010 BMX World Championships (Pietermaritzburg, South Africa). Cowell et al. (3) stated that 44% of the duration of a race was spent pumping, while the current study only found a variation of 19.50 ± 4.25% in lap times between the pumping and nonpumping trials (Figure 2).
Surface EMG was used in the study to confirm that the appropriate technique was performed in the appropriate trial. It was anticipated that the pumping trial would produce relatively greater muscle activation, thus confirming the pumping technique was being implemented. However, the results from the sEMG data, however, revealed no significant differences in muscle activation between any of the muscle groups (Figure 3) during the pumping and nonpumping trials. This is despite confirmation that the technique was implemented appropriately through the video analysis of the trials. There are 2 possible explanations for the nonsignificant differences in muscle activation; (a) the shift from dynamic to isometric muscle contraction and (b) the change in technique causing a greater impact on the rider during nonpumping trials.
The pumping technique is a dynamic movement that requires a rider to push down on the bike at the top of a hill to gain extra velocity from the downward slope. According to Cowell et al. (4) the whole body is used when pumping, including the lower body, although riders have commented that the contribution of the upper body “feels” greater. Force is generated in the lower body through a single hip and knee extension on the downward slope of a hill, while force is applied simultaneously to the bars of the bike by the upper body. As a result, this transfer of force from the rider to the bicycle results in the production of velocity. This movement pattern requires dynamic muscle contraction in both the upper and lower body. When the riders refrain from pumping, they isolate their upper and lower body maintaining a standing position on the pedals of the bike, with the rider's arms and legs extended and held in this position.
The second possible explanation for the nonsignificant sEMG data recorded may be the influence of the change in technique and the resultant impact on the rider. As previously explained, the fluid action of the pumping technique when riding the rhythm section limits the impact on the rider. When riders refrain from performing the pumping technique, the impact of the bicycle wheels on the ascent and decent of the hills in the rhythm section are transferred through the bicycle to the rider. As a result this could have been recorded by the sEMG as the muscles have to stabilize the body to remain upright on the bike.
The findings of the present study support this supposition, and it is proposed that these isometric contractions contributed to greater impact forces being transferred to the muscles, and may explain why the recorded sEMG data were comparable with the magnitudes observed during the more dynamic pumping technique. During pumping, although the muscles were actively engaged in trying to increase velocity, the greater flex in the elbow, hip, and knee joints may have aided the attenuation of forces on landing. As such, further analyses of the 2 techniques are warranted using 3D kinematic assessments, to quantify any biomechanical differences.
Coaches, riders, and researchers are constantly looking for new and novel areas of training that can elicit and increase performance in athletes. Bicycle Motocross cycling is no exception; however, there is limited academic knowledge for the intervention of training in the sport. The implications of the current study include further advances into the sport, and offer a new insight into training priority. The findings from this study demonstrate that the technique of pumping contributes 21.81 ± 5.31% to the rider's velocity production. These findings should assist coaches, riders, and researchers in the design of BMX training programs. A multidisciplinary approach could be adapted to support technique and strength development. The implementation of an upper-body strength-training program that develops the riders' functional stability could result in a more effective kinetic chain, thus aiding the rider to perform the technique of pumping more effectively.
The authors thank Elite Trax Inc. for allowing to use the track diagram in this article. The authors also express their gratitude to the Irish Cycling Coach Jeremy Hayes for his time and dedication to the research project. The authors confirm that there are no conflicts of interest for this work.
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