Badminton is a popular sport and one of the fastest racquet sports (Lees, 2003). The lunge step is one of the most frequently performed movements in badminton, accounting for approximately 15% of the total movements in a game (Kuntze et al., 2010; Mei et al., 2017). Performing a good lunge step is usually associated with high flexibility. In addition, badminton players must react by moving rapidly with powerful jumps and agile footwork throughout a game. Players must repeat actions quickly with high speed and intensity. Therefore, players need excellent joint range of motion (ROM), power, and agility (Tiwari et al., 2011; Wong et al., 2019).
Warm-up exercise is critical prior to participation in sports. It improves performance and may avoid injury (Woods et al., 2007). Muscle strain injuries usually occur during movements that involve rapid acceleration/deceleration and sprinting (Opar et al., 2012). Dynamic stretching (DS) is the most commonly suggested warm-up protocol (Turki et al., 2019). The DS technique involves a stretch to lengthen the muscle, and it is performed by moving parts of the body and gradually increasing reach and speed of movement (Behm and Chaouachi, 2011). It often mimics movement patterns performed during subsequent exercise. DS provides a more sport-specific warm-up exercise, and as a precursor, it increases body temperature, improves nerve conduction, and increases sports performance (i.e., jump height, sprint speed, and agility) (Chaouachi et al., 2010; Opplert and Babault, 2018; Perrier et al., 2011). However, reports regarding the effect of DS on muscle stiffness are conflicting, indicating that DS may cause increased or reduced muscle stiffness (Chen et al., 2018; Iwata et al., 2019; Pamboris et al., 2018).
Vibration foam rolling (VFR) combines a foam roller with vibration; the roller serves as a foam rolling tool that targets a particular muscle group. It has been suggested as an alternative warm-up method (Lee et al., 2018; Lyu et al., 2020). Beneficial outcomes of VFR include remobilizing soft-tissue compliance to enable longer muscle length and increasing blood flow and circulation to soft tissues conducting rolling on the soft tissue (MacDonald et al., 2013). Concurrently, the additional transmission of mechanical oscillations to the target muscle may increase the number of motor units recruited (Cochrane, 2011). However, few studies have investigated the effectiveness of VFR, particularly for athletic performance. Thus far, studies have focused on ROM (Cheatham et al., 2019; Garcia-Gutierrez et al., 2018; Lee et al., 2018; Lim et al., 2019; Lim and Park, 2019; Lyu et al., 2020), pressure pain threshold (Cheatham et al., 2019; Romero-Moraleda et al., 2019), electromyography activity (Lim et al., 2019), isokinetic muscle strength (Lee et al., 2018; Lyu et al., 2020), perceived joint stability (De Benito et al., 2019), dynamic balance (Lee et al., 2018), and vertical jump (Lim and Park, 2019). However, these studies have focused on the knee or ankle musculatures rather than combined effects on the whole body--specifically, when the technique targets upper and lower extremities and the lower back. Furthermore, the aforementioned VFR studies were conducted in healthy participants or participants involved in recreational activities rather than in athletes. Scientific evidence is inadequate; little is known about sports performance following the use of VFR as a warm-up regime.
The most beneficial warm-up protocol remains uncertain, particularly for combination warm-up exercises. Moreover, no study has examined the effects of DS combined with VFR on badminton athletes. Studying the effects of combination warm-ups on sports performance can provide evidence that can help athletes, coaches, and clinical professionals to decide whether to add the VFR protocol to DS. Accordingly, this study compared the acute effects of DS as well as DS followed by VFR during warm-up on flexibility, muscle stiffness, power, and agility in young adults. The primary outcome was knee ROM. The secondary outcomes were muscle stiffness, countermovement jump (CMJ), and agility. We hypothesized that DS as warm-up exercise can not only increase ROM, CMJ height, and agility, but increase muscle stiffness. In addition, VFR can offset muscle stiffness.
The study protocol was approved by the Yuan's General Hospital Institutional Review Board (Approval Number: 20180209B) and Human Research Ethics Committee in the spirit of the Helsinki Declaration. Participants were informed of the benefits and risks of the study, and they signed an informed consent form before participating. Totally, 40 college badminton players (25 male and 15 female students) participated in two trials: (1) DS and (2) DS followed by VFR (Figure 1). Characteristics of participants are presented in Table 1. The inclusion criteria were as follows: membership in a school badminton team, 20-30 years of age, and no incidence of musculoskeletal disorder in the preceding 6 months. The exclusion criteria were as follows: musculoskeletal disease or neurological impairment, cardiovascular or respiratory disease, irradiation pain/radiation pain transferred to the lower extremities, previous surgery, and taking medication (e.g., anti-inflammatory or muscle relaxants) during the preceding 6 months.
This study was a crossover study with a within-subject design. Tests were performed in an indoor badminton gym at National Sun Yat-sen University. Each participant did the exercises at approximately the same time of day (18:0020:00). Before the assessment session, participants performed a familiarization session, in which they were instructed by a certified physiotherapist on how to perform DS and VFR exercise regimes. During this orientation, par ticipants were familiarized with the procedures and practiced with the assessment tools and equipment. Participants were asked to maintain normal training programs but to avoid vigorous exercise at least 24 hours before the tests. Each participant performed the two protocols on separate occasions in a randomized order, with an interval of 48 hours (Su et al., 2017). Participants were individually guided by a certified physical therapist for performing both DS and VFR. The target muscle groups were the bilateral shoulder, anterior thigh, posterior thigh, posterior calf, and lower back. Participants performed the pretests in the following order: muscle stiffness, flexibility, CMJ, and agility tests. After completion of pretests, participants did the warm-up exercise (DS or DS + VFR) in a counterbalanced order. Posttest measurements were conducted in the same order as pretest measurements.
Before data collection, examiners were well-trained in conducting the flexibility, muscle stiffness, CMJ, and agility tests.
The primary outcome was knee ROM. The knee flexion ROM of participants was measured using Ely's test, which is also used for testing quadriceps femoris muscle flexibility. This test was shown to have an intraclass correlation coefficient (ICC) of 0.91, which represents high reliability (Piva et al., 2006). With participants in the prone position, the examiner aligned the plastic goniometer with the axis of the knee joint; the stationary arm represents the greater trochanter of the femur, and the passively moving arm represents the lateral malleolus of the ankle. When the hip flexes as the knee is flexed, the pelvis should remain on the floor, and compensation by hyper-lordosis of the lumbar spine is avoided. The outcome measured was rectus femoris tightness by the same researcher, which was used to determine the termination of knee flexion ROM. The researcher subjectively perceived to inability to push the leg farther without any body compensation and measured the ROM. The average measurement of two trials was recorded. In this study, the ICC was 0.821, suggesting high test-retest reliability. In addition, the minimum detectable change (MDC) value was calculated to be 2.2[degrees], corresponding to a standard error of...