According to the 2021 National Survey on Sports Participation in Korea, bodybuilding accounts for the highest proportion among sports activities of individuals in their 20s, comprising 30.8% [1]. Bodybuilding primarily involves resistance training, and the high participation rate among young adults indicates a considerable engagement in resistance exercises. People unfamiliar with resistance training because of a lack of regular physical activity may experience muscle damage due to sudden muscular contraction [2-4]. Such abrupt muscle damage can cause injuries or muscle soreness, restricting continuous participation in exercise [5]. Thus, effective recovery methods are necessary to alleviate muscle pain and damage.

Methods for muscle relaxation include foam rolling, massage, and stretching. Among them, foam rolling is the most commonly used tool for muscle relaxation because of its cost-effectiveness, convenience, and time efficiency [6-8]. Foam rolling helps reduce muscle stiffness by relaxing the adhered muscle fascia, thereby increasing joint flexibility and alleviating muscle fatigue and pain [9]. However, it has been observed that the muscle relaxation effects of foam rolling may be temporary, with limitations in sustaining long-term effects [10].

Recently, vibrating foam rollers, which integrate vibration with conventional foam rollers, are being utilized in practical applications. Among recovery methods for muscle fatigue, vibration stimulation inhibits sympathetic nervous system activities, allowing relatively prolonged muscle relaxation effects [11,12]. Combining vibration stimulation with foam rolling has helped sustain such effects [13], enhance mitochondrial biogenesis, and reduce inflammatory cytokines while activating the FAK pathway to promote muscle fascia decomposition [14]. This combination may further reduce muscle stiffness [14,15]. Thus, the synergistic contribution of the combined vibration and foam rolling stimulation may positively alleviate muscle damage and improve the joint range of motion (ROM) [11,12]. Accordingly, recent research has compared vibration foam rollers that integrate vibration functionality into traditional foam rollers [16]. Kasahara et al. [13] conducted a crossover study involving adult males and compared the effects of vibration foam rollers and regular foam rollers applied to the quadriceps femoris on muscle stiffness. They found that stiffness significantly decreased immediately after application of regular foam rollers; however, it returned to pre-intervention levels 20 and 30 minutes after application. Conversely, the application of vibration foam rollers significantly decreased stiffness not only immediately post-application but also 20 and 30 minutes post-application. Alonso-Calvete et al. [16] also suggested that vibration foam rollers demonstrate longer-lasting effects than regular foam rollers do. Typically, vibration foam rollers are used either before or after exercise. However, their indiscriminate use in practice persists because of unclear optimal timing for effective recovery from muscle and tissue damage and pain caused by resistance exercise. Thus, further research should determine the optimal timing of the application of vibration foam rollers in practical settings. Applying a vibration foam roller before resistance exercise may disrupt cross-bridges between actin and myosin filaments formed naturally when muscles are not contracted, thereby reducing tissue stiffness [17]. However, immediately after disrupting, cross-bridges gradually reattach; because of elastic recoil, the reattachment time can be shortened, potentially returning quickly to a stiff state [18]. Following resistance exercise, stimulation from a vibration foam roller can reduce the number of cross-bridges that increased due to elastic recoil, but subsequent reattachment may proceed slowly as elastic recoil does not occur thereafter [4]. This phenomenon suggests that it may effectively reduce stiffness after resistance exercise. Therefore, we hypothesized that applying a vibrating foam roller after resistance exercise may be more effective than that before resistance exercise. While conventional foam rollers have positively affected muscle recovery, they are limited by temporary efficacy. As such, further direct comparative studies should be performed on the recovery outcomes of the timing of the application of vibrating foam rollers, which can be used before or after resistance exercise in practical settings to complement these effects. Therefore, this study aimed to determine the optimal timing of the application of vibrating foam rollers, that is, before and after resistance exercise, by comparing the changes in serum creatinine kinase (CK) levels, ROM, and muscle stiffness.

This study aimed to compare and analyze the effects of pre- and post-resistance exercise application of vibrating foam rollers on serum CK levels, muscle stiffness, and ROM in healthy adult males.

CK is commonly studied as an indicator of muscle damage; it typically increases when a muscle is injured. In this study, changes in CK levels showed that immediately post-exercise and at 24 and 48 hours post-exercise, CK levels were significantly lower in VF-POST than in CON; conversely, CK levels in VF-PRE were lower immediately post-exercise than those in CON, but they did not show significant differences at 24 and 48 hours post-exercise. Imtiyaz et al. [19] revealed that the CK levels of healthy females applying 50 Hz vibration stimulation for 5 minutes prior to endurance exercise were significantly lower 48 hours later than those of the control group without vibration stimulation. Kim et al. [20] applied vibration massage on the central part of the biceps brachii at 60 Hz for 5 minutes in a cross-over design, stimulation before resistance exercise, and stimulation after a washout period; then, they compared the changes in CK levels at 24, 48, and 72 hours later. They found that CK levels were significantly lower when vibration stimulation was applied after resistance exercise than when it was applied before resistance exercise. During eccentric contractions, muscle damage occurs due to sarcomere weakening, leading to the leakage of intracellular CK proteins into the bloodstream, resulting in increased plasma levels [21]. Vibrating foam rollers increase nitric oxide levels, promoting blood flow and enhancing endothelial function within blood vessels. They facilitate the removal of metabolic waste and activate muscle spindles via tonic vibration reflex, simultaneously stimulating muscle contraction and periarticular muscles. This activation increases heat generation, thereby reducing elastic stress in muscles and connective tissues, potentially lowering circulating CK levels. Consistent with previous findings, our results suggested that vibrating foam rollers might positively reduce CK levels. Additionally, the application of vibrating foam rollers after resistance exercise was likely more effective in reducing CK levels than that before resistance exercise.

Muscle stiffness can increase because of the accumulation of fatigue substances and muscle damage caused by eccentric contraction. Nevertheless, it can be reduced by self-myofascial release and vibration therapy.

In this study, we measured the muscle stiffness of the right rectus femoris. Immediately post-exercise and at 24 and 48 hours post-exercise, the stiffness in VF-POST was significantly lower than that in CON. At 48 hours post-exercise, stiffness significantly differed between the VF-PRE and CON groups, but no significant difference was observed immediately post-exercise and at 24 hours. Pournot et al. [4] reported that the shear modulus of the biceps brachii significantly decreased after localized vibration stimulation at 55 Hz on one arm subjected to a biceps curl at 70% 1RM in healthy adults. This result was consistent with the findings of the present study. Shear modulus is an indicator of muscle stiffness; it can increase because of the increased cross-bridge formation between myosin heads and actin following resistance exercise [22]. These cross-bridges can be partially disrupted by vibration stimulation [18], potentially reducing the increased stiffness observed after resistance exercise. However, applying vibration foam rollers before resistance exercise may not effectively reduce post-exercise stiffness because cross-bridges reattach shortly after disruption, and such reattachment increases with the subsequent contractile activity. Thus, applying vibration foam rollers after resistance exercise could be the most effective timing for reducing muscle stiffness.

The right knee flexion ROM was significantly lower in VF-POST than in CON immediately post-exercise, at 24 hours post-exercise, and at 48 hours post-exercise. Similarly, the right knee flexion ROM in VF-PRE was significantly lower immediately post-exercise than that in VF-POST. Resistance exercise-induced decreases in ROM may be attributed to inflammation caused by skeletal muscle damage, leading to fiber disruption and subsequent fibrous tissue adhesion [5]. Rahmani Nia et al. [23] induced muscle soreness in healthy adult males by performing leg extensions at 75% of 1RM with 3 minutes intervals until fatigue occurs to assess recovery effects. They observed that knee flexion ROM significantly decreased at 24 and 48 hours post-exercise compared with baseline measurements. Vibrating foam rollers can enhance tissue extensibility and muscle resilience by promoting blood flow and increasing muscle temperature [24,25]. Furthermore, stimulating Ruffini and Pacinian receptors, which inhibit sympathetic activities, can increase muscle relaxation [26]. In the present study, vibrating foam rollers possibly helped increase the ROM that decreased after resistance exercise. Lau and Nosaka [27] reported that the recovery of the elbow flexion ROM was significantly faster in the group that used Cybex to perform maximal voluntary eccentric exercises for the elbow joint followed by local vibration massage stimulation than in the control group. They observed that elbow flexion ROM, which typically decreases after eccentric exercise, recovered more rapidly with vibration stimulation. Conversely, Magoffin et al. [28] reported that applying whole-body vibration stimulation at 40 Hz for 60 seconds in five sets before maximal voluntary eccentric exercises with Biodex significantly decreased the knee flexion ROM at 24 and 48 hours post-exercise compared with baseline measurements.

Consistent with the present research, previous studies indicated that the post-eccentric contraction application of vibration foam rollers is effective in enhancing the ROM. The present results also showed that the extent of the decrease in ROM with VF-PRE was greater than that with VF-POST. This result suggested that the application of vibration foam rollers after resistance exercise positively influenced the reduction in muscle stiffness. Repetitive eccentric contractions increase the muscle stiffness after the resistance exercise, thereby decreasing joint flexibility. The stiffness of VF-POST was the lowest among the changes in muscle stiffness measured immediately post-exercise, at 24 post-exercise, and at 48 hours post-exercise. The changes in ROM also indicated that VF-POST effectively relaxed the stiffened muscles and tissues because of eccentric contractions, thereby positively influencing joint flexibility. Therefore, vibration foam rollers should be applied after resistance exercise to positively influence the recovery of knee flexion ROM.

This study confirmed that the application of vibrating foam rollers after resistance exercise is more effective than that before exercise in decreasing CK levels, improving joint flexibility, and reducing muscle stiffness. It also provides foundational data on the timing, frequency intensity, and duration of the use of vibrating foam rollers for practical application. However, this study has several limitations. Firstly, it only included adult males as participants. Secondly, we were unable to control for variations in dietary intake, sleep duration, and lifestyle habits among the study subjects. Future research should address the limitations and investigate how varying the frequency and duration of vibrating foam roller use affects muscle damage recovery.