J Sci Cycling.Vol.

4(1), 28-32

RESEARCH ARTICLE Open Access

The effect of bicycle seat-tube angle on

muscle activation of lower extremity
1 1 2
Chia-Hsiang Chen * , Ying-Hao Huang , Tzyy-Yuang Shiang

Abstract
To investigate lower extremity muscle activation at various bicycle seat-tube angles. Twenty healthy participants (10
males and 10 females) with right dominant leg were recruited for this study. The study recorded the rectus femoris,
hamstring, tibialis anterior, and gastrocnemius medialis in five different seat-tube angles conditions at 59, 69, 79, 89,
99 degrees. One-way analysis of variance with repeated measures was used to analyze all the data. The level of
significance was set at = .05. A steeper bicycle seat-tube angle reduced the muscle activation of the rectus
femoris, hamstring and gastrocnemius during the downstroke phase. However, when the seat-tube angle was
increased to 99, the muscle activation of the rectus femoris and hamstring increased. In addition, the activation of
tibialis anterior muscle decreased as the seat-tube angle increased. Lower extremity function can be changed by
adjusting the seat-tube angle. At seat-tube angles of less than 90, a steeper seat-tube angle can enhance pedaling
efficiency. For lower extremity, a seat-tube angle greater than 90 can be used for rehabilitation and training.
Keywords: EMG, saddle positions, cycling, bike fitting

* Contact email: doof75125@hotmail.com (CH Chen) power output and less oxygen consumption than an
STA of 68 (Price and Donne 1997). An STA between
1
Department of Physical Education, National Taiwan Normal University, 72 and 76 yields optimal cycling performance
Taiwan, Province of China (Hunter et al. 2003). When the STA increased to 81,
Department of Athletic Performance National Taiwan Normal
2 muscle fatigue was delayed (Garside and Doran 2000).
University, Taiwan, Province of China Moreover, when STA increased to 82, power output
__________________________________________________
increased and muscle activation was reduced (Ricard et
Received: 28 September 2013. Accepted: 10 April 2014.
al. 2006). Contradictory to the study above, researches
showed that a change in STA (7381) exerts no effect
on heart rate variability (Jackson et al. 2008), the range
Introduction
of motion of lower extremity joints, energy
Increasing the bicycle seat-tube angle (STA) can
metabolism, or muscle energy consumption (Bisi et al.
decrease the torso angle, reduce wind resistance, and
2012).
enhance aerodynamic effects (Hausswirth et al. 2001),
The discrepancies in cycling literatures may be due to
thereby enhancing performance during racing
different bicycle frames used in those studies. In most
competition. The bicycle seat tube angle is defined as
existing studies, position (seat and handlebar) was
the angle between seat tube and horizontal axis at
adjusted based on the existing bicycle frame geometry
bottom bracket. Previous study has shown that different
(Hunter et al. 2003; Ricard et al. 2006), and the
lower extremity joint angle can change the lower-
adjustable STA was typically limited by the original
limbs muscle activation and kinematics (Chen et al.
bicycle design (Bisi et al. 2012). In addition, adjusting
2013b). In addition, increased height of saddle position
the STA altered the distance between the bicycle
can alter a riders posture of knee angle resulting in
handlebar and saddle, affecting the torso angle and
muscle strength and contraction velocity change
thereby possibly resulting in inconsistent experiment
(Browning et al. 1992; Reiser et al. 2002; Savelberg et
results. Therefore, a bicycle frame that allowed the
al. 2003). Therefore, STA is extremely crucial to affect
STA to be altered in accordance with the distance
anatomical advantage and performance of bicycle.
between the bicycle handlebar and saddle may provide
Currently, the road-bike STA is between 72 and 76
more insightful information regarding the relationship
(Hunter et al. 2003; Ricard et al. 2006) and the STA for
between bicycle and lower extremity geometries.
triathlon is between 78 and 82 (Price and Donne
Furthermore, most studies investigating bicycle saddle
1997). Triathletes believe that a steeper STA (~80) adjustment focused on elite cyclists (Bini et al. 2012;
can increase power output, making it more efficient, Bisi et al. 2012). However, the majority of bikers are
and a comfortable posture during cycling. (Hunter et al. for the purpose of regular exercise and leisure activity.
2003; Price and Donne 1997). Therefore, the purpose of this study was to investigate
Previous research has indicated that at STAs of 76, the lower extremity muscle activation at various STAs.
83, and 90, oxygen consumption and average heart On the hypothesis was that a steeper bicycle STA will
rate were reduced compared with an STA of 69 (Heil reduce lower extremity muscle activation during the
et al. 1995). In addition, an STA of 74 yields a higher

2015 Chen; licensee JSC. This is an Open Access article distributed under the terms of the Creative Commons Attribution License
(http://creativecommons.org/licenses/by/3.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original
work is properly cited.


Chen (2015). The effect of bicycle seat-tube angle on muscle activation of lower extremity, 4(1): 28-32

downstroke and upstroke phases on recreational bicycle shown in Figure 1. The central position was defined at
riders. the trunk flexion in 45relation to a non-sloping top
tube (Silberman et al. 2005) and seat position was set at
Materials and methods 95% of trochanter length (Sanderson and Amoroso
This study was approved by the Institutional Review 2009) in position of STA at 79 degrees. The order of
Board of the local Medical University Hospital, and conditions was based on a counter balance design to
informed written consent was obtained from all prevent order bias. Each participant performed each
participants prior to testing. Twenty healthy condition within 2 min, with a 2-min break between
participants (10 males and 10 females) with right trials to prevent muscle fatigue. Metronomes were used
dominant leg were recruited for this study and, the to control the pedaling cadence at 90 rpm, and no extra
body composition of the participants were shown in resistance was applied on the ergometer. When the
Table 1. The inclusion criteria for participating in this participants riding patterns became stable and
study was 100 min/week minimum cycling. None of consistent (typically 45 cycles after the start of the
the participants had received serious injuries to their trial), we marked the signals and recorded the EMG in
lower extremities causing them to seek medical help in the muscles of lower extremities for 1 min. One
the year before the study was conducted. minutes EMG truncated starting at fifth cycling cycles
To investigate muscle activity in the lower extremities, was analyzed.
electromyography signals were obtained from the This study defined the period of leg activity according
muscle groups on dominant sides, including the rectus to the crank angle. The crank angle at 0 was equal to
femoris (RF), hamstring (HAM), tibialis anterior (TA), top dead center, 0180 was defined as the downstroke
and gastrocnemius medialis (GAS). The electrode period, and 180360 was defined as the upstroke
placements are described as follows: (1) For the RF, the period (So et al. 2005).
electrode was placed at the midpoint between the The LabVIEW 8.5 (National Instruments, USA)
anterior superior iliac spine (ASIS) and the superior software was applied to analyze the EMG signals. A
aspect of the patella; (2) For the HAM, the electrode fourth-order Butterworth filter was used to filter and
was placed at the midpoint between the distal ischial smooth the EMG raw data. The EMG signals were
tuberosity and the popliteal fossa; (3) For the TA, the filtered using a band pass filter (10-500 Hz), and then
electrode was placed in the upper-third of the muscle, processed using full-wave rectification and were
which extends from the tibial head to the medial smoothed at a low frequency of 6 Hz to obtain a linear
malleolus; (4) For the GAS, the electrode was placed at envelope graph. The EMG data were normalized using
the one hand breadth below the popliteal crease on the the maximal voluntary contraction (MVC) (Robertson
mass of the calf. Active electrodes (TSD150 series, 2004).
Biopac Systems Inc., Goleta, CA, USA) were used to An one-way analysis of variance (ANOVA) with
record muscle activation signals. The reference repeated measures was used to analyze all the data.
electrode was placed on the lateral malleolus of the Greenhouse-Geisser correction was employed when
right ankle. The electrodes (5 mm in diameter) were data violated the sphericity assumption. Post hoc were
positioned with an interelectrode distance of 20 mm. performed using Bonferroni when main effects were
The skin where the electrodes were placed was shaved significant after ANOVA. The level of significance was
and cleaned with alcohol. And the skin preparation set at = .05. Partial eta squared (partial 2) and
before application of surface electrodes ensured that the observed power values were calculated to complete the
interelectrode resistance was below 5 Kohms. The analysis. Partial 2 was used to calculate effect sizes,
EMG signal sampling rate was set at 1000 Hz (pre- with outputs of 0.5 or greater considered a large effect
amplifier: common mode rejection ratio = 95 dB; size, 0.1-0.5 a moderate effect size and less than 0.1 a
impedance = 100 M ohms; gain = 350). All EMG small effect size (Field 2009).
signals were recorded using an acquisition system
(Biopac MP150, Biopac Systems Inc., Goleta, CA,
USA) into a personal computer. Before the start of the
cycling trials, the electrodes were adhered to
participants muscles to record maximal voluntary
isometric muscle contraction signals, which were used
as the normalized standard signals. The MVC tests
were completed in accordance with the manual muscle
testing by Perotto and Delagi Table 3. The body composition of the participants
(2005) method. Males (n=10) Females (n=10)
In order to thoroughly
understand the effect of Age (year) 24.7 1.9 (rang: 22.8~27.8) 24.0 2.0 (rang: 20.9~27.9)
bicycle STA on lower
Weight (Kg) 69.2 6.2 (rang: 58.7~80.0) 55.1 4.2 (rang: 49.2~59.3)
extremity muscle activation.
Wider range of different STA Dominate leg length (cm) 89.3 2.5 (rang: 85.5~94.0) 82.4 3.2 (rang: 78.0~87.5)
conditions at 59, 69, 79, 89, 99
degrees were collected as

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 J Sci Cycling. Vol. 4(1), 28-32 Chen et al.

Figure 1. Five riding seat positions of different seat-tube angle conditions.

Results
The one-way ANOVA revealed that significant Discussion
difference was found for the RF (F(2.471, 46.941)=7.908, The results indicated that a steeper bicycle STA
p=0.001, partial 2 = .294), HAM (F(1.750, 33.257)=8.633, reduced the muscle activation of the gastrocnemius,
p=0.001, partial 2 = .312), TA (F(2.070, 39.326)=29.298, rectus femoris, and biceps femoris during the
p=0.000, partial 2 = .607,) and GAS (F(2.618, downstroke phase, except for 99. In addition, the
49.747)=68.632, p=0.000 partial
2
= .783,) at the activation of tibialis anterior muscle decreased as the
downstroke period. Post hoc comparisons showed that STA increased in all conditions.
the EMG of seat position at 99 STA were significantly Previous studies showed that the STA was increased
higher than 69, 79, 89 STAs, as well as the EMG of from 73.5 to 78, the muscle activation of the biceps
seat position at 59 STA were significantly higher than femoris and gastrocnemius decreased (Bisi et al. 2012;
89 STA on RF, HAM, TA and GAS. Furthermore, the Ricard et al. 2006). On the other hand, a similar change
muscle activation of HAM showed no significant in STA (73 to 81) exerted no effect on energy
difference between 99 STA and 69 STA. On the consumption on triathletes (Bisi et al. 2012; Jackson et
other hand, the results showed that the EMG of seat al. 2008). However, this study investigated recreational
position at 59 STA were significantly higher than 69, cyclist, and found that a change in the bicycle STA
79 STAs on TA and GAS. Mean SD of the muscle altered lower extremity muscle activity. Previous
activation at different STAs are shown in Table 2. research demonstrated that torso anteversion increased
The one-way ANOVA revealed that significant and hip range of motion altered with increased STA.
difference were found among the RF (F(2.604, (Hausswirth et al. 2001; Hunter et al. 2003; Savelberg
49.481)=6.290, p=0.002, partial = .249), HAM (F(1.553,
2 et al. 2003). Studies also indicated that moving the
saddle position forward altered the range of motion of
29.129)=39.724, p=0.000, partial = .676), and GAS
2

(F(2.310, 43.896)=3.738, p=0.026 partial 2 = .696,) at the the entire lower extremity geometry (Bini et al. 2012;
upstroke period. Post hoc comparisons showed that the Chen et al. 2013a) and affected muscle activation and
EMG of seat position at 59 STA were significantly length, as well as muscle contraction velocity (Hug and
lower than 89 STA on RF. The EMG of seat position Dorel 2009; Reiser et al. 2002; Savelberg et al. 2003),
at 99 STA were significantly higher than 59, 69, 79 resulting in better power output during cycling (Bini et
and 89 STA on HAM. The power values as a range al. 2012; Reiser et al. 2002; Savelberg et al. 2003).
(0.931~0.999) for all variables since they are all According to our results, for recreational cyclists under
relatively high. the same resistance load, increasing the STA without
Table 2. The muscle activation (% MVC) at different STAs (59, 69, 79, 89 and 99 degrees) on lower extremity muscles (RF, HAM, TA and GAS) during
the downstroke and upstroke phases. All values expressed as MeanSD.
phase 99 89 79 69 59
RF Downstroke# 8.51 2.28 6.63 0.83a 7.08 1.80a 7.27 1.62a 7.97 1.19b
Upstroke# 7.59 3.11 7.17 2.31 7.67 2.88 8.64 4.22 8.67 3.01b
HAM Downstroke# 8.03 1.76 6.61 0.97a 6.54 0.78a 7.01 0.92c 7.27 0.92b,c
Upstroke# 10.44 2.66 7.28 1.85a 6.64 0.96 a 6.34 0.85a 6.32 0.83a
TA Downstroke# 10.81 2.91 8.80 2.27a 7.23 1.37a,b 7.13 1.83a,b 6.63 1.23a,b
Upstroke 11.32 4.68 10.49 3.73 9.34 3.45 9.84 4.76 9.45 3.70
GAS Downstroke# 12.95 1.94 16.53 2.27a 18.61 2.14a,b 20.50 3.26a,b 24.05 3.62a,b,c,d
Upstroke# 10.29 2.83 10.59 3.08 11.71 3.28 11.63 3.47 12.21 3.95
#: Indicate significant difference among five riding seat positions of different STAs conditions (p < .05).
a: Indicate that 99 STAs values were significantly higher (or lower) than other STAs values (p < .05).
b: Indicate that 89 STAs values were significantly higher (or lower) than other STAs values (p < .05).
c: Indicate that 79 STAs values were significantly higher (or lower) than other STAs values (p < .05).
d: Indicate that 69 STAs values were significantly higher (or lower) than other STAs values (p < .05).

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Chen (2015). The effect of bicycle seat-tube angle on muscle activation of lower extremity, 4(1): 28-32

Figure 2. RMS EMG envelope for 4 lower extremity muscles obtained from different STAs of 59, 79 and 99 degrees. RF, rectus femoris; HAM,
hamstring; TA, tibialis anterior and GAS, gastrocnemius medialis.

exceeding 90 reduced muscle activation during load, a 99 STA can increase thigh muscle activation
bicycling. Previous research showed that the same during pedaling. A riding position with an STA of 99
power producing with a reduced demand on muscle is a suitable choice for patients who require lower
activation during the cycling indicating better pedaling extremity rehabilitation. In addition, moving the
efficiency (Blake et al. 2012) . bicycle saddle forward can reduce the shear forces
In addition to performance, cycling exercise has also across the knee joints (Bini et al. 2013). Thus, this
been used for rehabilitation for knee injuries. (Fleming study found that a bicycle frame with a steeper STA
et al. 1998; Kutzner et al. 2012). However, the might be used for knee rehabilitation after knee
anatomical geometry that can provide enhanced muscle operation.
training have not been identified. Previous research
showed that a relatively backward saddle position, Practical applications
pedaling required a greater knee flexion angle (Bini et This study found that various bicycle STAs affected
al. 2012) and required ankle joints to produce greater lower extremity muscle activation, particularly for
planar flexion (Price and Donne 1997; Rottenbacher et general bicycle enthusiasts. Lower extremity
al. 2009). Intriguingly, this study found that at a small function can be changed by adjusting the STA. A
STA (59) can increase the electromyographic steeper STA can reduce the load on lower extremity
activation of the biceps femoris and gastrocnemius. muscles which might enhance pedaling efficiency at
Noticeably, this study found that the muscle activation SATs between from 59 to 89. For lower extremity
of the rectus femoris and biceps femoris decreased as training, a STA greater than 90 may be useful for
the STA increased from 59 to 89, except when STA cycling to increase the load on lower extremity
increased to 99. At an STA of 99, the body moved muscles and achieve effective muscle training. In
forward and the riding posture was similar to a standing addition, a bicycle frame with a steeper STA would
riding position. A standing riding position allows the be beneficial for knee rehabilitation after knee
rider to use their body weight to increase pedaling operation.
strength and increase lower extremity muscle activation Acknowledgment
(Duc et al. 2008). Therefore, at an STA of 99, cycling This study was funded by Aim for the Top University
induced greater thigh muscle activation, in particular in Project of the National Taiwan Normal University
the biceps femoris, muscle activation occurred during and the Ministry of Education, Taiwan, R.O.C.
both downstroke and upstroke phases.
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