Effects of core stability and feedback music on upper body mediolateral movements during cycling | BMC Sports Science, Medicine and Rehabilitation

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This study enrolled 71 healthy participants (29 males and 42 females; mean age: 22.3 ± 2.2 years; mean weight: 166.6 ± 8.8 kg) who did not experience pain while cycling. The two independent variables in this design were core stability and feedback music, and the dependent variables were amplitude (amp) and symmetry index (SI) of mediolateral head motion during cycling. Participants were assessed for core stability using the Sahrmann Core Stability Test (SCST), following which they were divided into two groups – ‘good core stability’ and ‘poor core stability’. The participants then cycled under two conditions: with and without feedback music. The effects of core stability and feedback music on amp and SI were then statistically analyzed.

Participants

Participants were recruited through a combination of online advertisements and flyers posted around the University campus and its vicinity. Interested individuals contacted the study team via the contact details provided on the advertisements. Prior to enrollment, potential participants were screened for eligibility based on the following inclusion criteria: (1) healthy individuals aged 18 and above, (2) individuals able to perform cycling without experiencing any pain, and (3) individuals who did not meet any of the exclusion criteria. Exclusion criteria involved pregnancy and the presence of vestibular, neurological, cardiopulmonary, psychological, or musculoskeletal disorders. To assess whether participants experienced pain during cycling, we asked them directly with the question: “Do you experience any pain while cycling?” If a participant responded affirmatively, they were excluded from the study. This method allowed us to ensure that all included participants were comfortable performing the cycling tasks required for our study. A total of 71 healthy participants (29 males and 42 females; mean age: 22.3 ± 2.2 years; mean weight: 166.6 ± 8.8 kg) were successfully recruited for the study. All participants in the study were amateur cyclists, meaning they knew how to ride a bicycle but did not cycle on a regular basis. This study did not specifically aim to measure cycling proficiency or frequency of cycling; however, all participants were capable of carrying out the cycling tasks required for our research. Their level of cycling experience can be broadly defined as beginner or casual, rather than intermediate, advanced, or professional. The study was in accordance with the principles as outlined in the Declaration of Helsinki. The participants provided written informed consent. The study was approved by the institutional review board of the Jeonju University.

Sahrmann core stability test (SCST)

The SCST was performed to evaluate core stability. It included five progressively more difficult tasks. The inflatable pad of a stabilizer pressure biofeedback unit (Chattanooga Group, Hixson, TN, USA) was placed in a natural lordotic curve while participants were placed in a crooked lying position. The pad was inflated to 40 mmHg before the task. A deviation of > 10 mmHg during the task indicated loss of stabilization of the lumbopelvic hip complex by the stabilizer muscles. Participants who completed a task without a deviation of > 10 mmHg were instructed to perform the next task. Performance (i.e., the ability to complete the tasks without a deviation of > 10 mmHg) was rated on a 5-point scale (Fig. 3). Participants were divided into two groups based on their SCST scores: ‘poor core stability’ (0–1) and ‘good core stability’ (2–5). This categorization was adopted from a previous study where an SCST of 1 or lower was deemed indicative of poor core stability [25]. The tasks were performed as reported previously [26].

Instruments

A high-resolution single IMU (BNO080; Ceva Technologies, Rockville, MD, USA) equipped with a triaxial accelerometer and triaxial gyroscope was embedded into a left-side wireless earbud (QCY-T1C; Dongguan Hele Electronics, Dongguan, China) to measure head angle (Fig. 1). IMU data were collected at 100 Hz. Each sample contained signed 16-bit acceleration output for x, y, and z axes. The acceleration outputs were transferred to a self-developed mobile app (DDoARi, Republic of Korea) via Bluetooth. The app calculated the mediolateral head angle in real time, similar to a previous study [27], and controlled the volume of music from the wireless earbud to provide feedback.

Feedback music

Feedback music was provided in real time to prevent excessive mediolateral head motion during cycling. If the mediolateral head angle exceeded a predefined threshold, the wireless earbud on the side of the head tilt was muted. Once the mediolateral angle returned to the set range, the muted earbud was unmuted (Fig. 2). For example, if the angle threshold was 10° and the head tilted > 10° to the right side, the earbud on the right side was muted; the muted earbud was unmuted when the mediolateral head angle was reduced to < 10°.

Cycling

Participants wore the wireless earbud, including the IMU sensor, in their ears to measure head angle in the frontal plane and receive feedback music. The cycling was performed on an indoor cycle (Iwha Sean Lee X ike Inc., Republic of Korea). The cycling speed was measured and monitored in real-time by a device installed on the cycle, and the speed was displayed on an installed monitor, which allows participants to maintain their target speed. The investigator supervised the experiment to ensure that the participants did not deviate from the target speed and provided continuous guidance to help them maintain the target speed. During warm-up, participants cycled for 5 min at their preferred speed. Then, after a 5 min rest period, the participants were instructed to cycle at the fastest speed possible; 70% of the measured maximum speed was set as the target speed.

After cycling at their fastest speed possible, participants were provided a 5-minute rest period to prevent undue fatigue. Following this rest period, participants engaged in trials at 70% of their measured maximum speed with and without feedback music. In the trial with no feedback, participants were asked to cycle at the target speed for 1 min. The mediolateral head angle was measured for 1 min during cycling at the target speed, and data from the final 40 s were analyzed. We chose to analyze the final 40 s of data from each trial for a couple of reasons. Firstly, as participants were trying to reach their set velocity, the time taken to achieve that speed varied between individuals. By focusing on the final 40 s, we ensured that we were analyzing data collected when participants were likely cycling at their target velocity. A value of 50% of the measured maximum mediolateral head angle was set as the threshold for feedback music, which was a medium tempo piece (125 beats per minute) in a minor key. The exact music piece used for feedback can be found at the following link: https://music.bugs.co.kr/album/20500357?wl_ref=list_ab_01_ar. After the trial with no feedback, participants cycled for 1 min at the target speed and received feedback. The participants rested for 3 min between the trials with and without feedback.

Symmetry

The maximal right and left head angles during each cycle were used to evaluate the range of mediolateral head motion and symmetry in head angle during cycling. Positive and negative signs for head angle represent the right and left directions, respectively. Therefore, the maximal value was the maximal right head angle, and the minimal value was the maximal left head angle (Fig. 4A).

The maximum and minimum values during each cycling cycle were recorded. The average difference between the maximum and minimum values indicated the range of mediolateral head motion:

$$ amp=\frac{\sum _{i}({max}_{i}-{min}_{i})}{n}$$

Here n is the number of peak values and max and min represent the maximum and minimum values during each cycling cycle, respectively (Fig. 4B).

Head angle symmetry during cycling was represented by the average of the maximal and minimum values:

$$ SI= \frac{\sum _{i}\left|({max}_{i}+{min}_{i})/2\right|}{n}$$

For a perfectly symmetric mediolateral head angle, the maximal right and left head angles should be equal (i.e., symmetry index [SI] = 0). Because the values for each direction have opposite signs, the closer the SI value is to 0, the more symmetric the head angle is in the frontal plane (Fig. 4B).

Statistical analyses

Independent variables included core stability and feedback music, while the dependent variables were amp and SI. A 2 × 2 mixed-model analysis of variance (ANOVA) was employed to assess the effects of core stability and feedback music on amp. Another 2 × 2 mixed-model ANOVA was used to evaluate the core stability and feedback music on SI, with a significance level set at p < 0.05. The partial eta squared value (η_p²) was calculated to describe the effect size.

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