Muscle soreness can be very uncomfortable, painful, and debilitating. The occurrence of soreness after exercise has been reported to be a deterrent and unwanted side-effect of exercise (16). Finding ways to decrease the occurrence or severity of muscle soreness is an important aspect of applied exercise science and health promotion.
Delayed-onset muscle soreness (DOMS) typically peaks within 24 to 48 hours after exercise and is resolved within 5 to 7 days. Various symptoms may be felt after exercise, which include pain, tenderness, swelling, and muscle stiffness (11). Previous studies suggest that there is no evidence of neural inhibition of damaged muscle (11) or changes in motor unit activation (15), leading to the idea that these symptoms are more likely related to the inflammatory process.
It is generally understood that eccentric exercise creates a disruption to the sarcomeres of the muscle tissue, and this in turn initiates an inflammatory process leading to muscle soreness. The function of the phospholipid bilayer cell membrane is to protect the cell and its contents and to help the cell remain at homeostasis by passive and active movement of chemicals. When there is a change in the chemical or molecular concentration in the cell, as in the influx of molecules, this will result in other changes in the cell, much like a positive feedback loop. This inflammatory process initially irritates the cell membrane, and a series of cellular changes results. Calcium accumulates in the cell, which activates the enzyme phospholipase. Phospholipase has the capability of drawing arachadonic acid from the phospholipid bilayer cell membrane and leads to the production of prostaglandins and leukotrines. Prostaglandins are directly involved in the pain that is perceived with DOMS by sensitizing type III and IV nerve fibers to chemical stimuli (5). Leukotrines produced from the arachadonic acid increase blood supply and attract neutrophils to the damaged part of the cell (5). The neutrophils then produce free radicals, which cause further damage to the cell membrane, and this in turn perpetuates the pain/inflammation cycle (5).
In addition, DOMS may cause some reduction in sport activities. For this reason, several studies have been designed to find ways to prevent and control DOMS. Massage, cryotherapy, stretching, homeopathy, ultrasound, and electrical current modalities have not been shown to be consistently effective (3). Furthermore, the evidence derived mainly from laboratory-based studies of stretching indicates that muscle stretching, both before and after exercise, does not reduce DOMS in young, healthy adults (8).
Whole-body vibration (WBV) has been suggested as a training and rehabilitation method. Consequently, in the last decade, several controlled studies have suggested the positive effects of WBV in strength or power development (6,14), flexibility (7,18), and bone mass (13). In addition, Bakhtiary et al. (1) found that the vibration training before eccentric exercise may prevent and control the DOMS. Increased blood flow to facilitate recovery and regeneration, increased flexibility, and possible pain inhibition may be mechanisms for such a decrease in pain. On the other hand, WBV after strength training has not been studied for its ability to prevent or decrease DOMS. The purpose of this research was to examine the efficacy of WBV (used as a massage tool and during flexibility exercise after strength training) to prevent or dampen the perceived pain after strenuous exercise among untrained individuals.
Experimental Approach to the Problem
To examine the influence of WBV on the extent of DOMS, untrained men were subjected to a strenuous, exhaustive exercise session. After the session, perceived pain was measured at various intervals for 3 days. One group performed intermittent bouts of WBV stretching and massage exercise, whereas the other group performed bouts of static stretching without WBV. Pain measures were compared between the 2 randomly created groups to evaluate for the potential alleviating effect of WBV.
Sixteen adult men (age, 36.6 ± 2.1 yr) volunteered to participate in this study. All subjects reported participation in aerobic exercise at least 2 days per week for 3 months before beginning the study; however, none reported resistance training sessions during that time. None reported any physical conditions that would impair their ability to perform high-intensity exercise. Participants provided informed consent to participate in this study, which was reviewed and approved by an institutional review board for research with human subjects.
Description of Exercise Session
After 10 minutes of moderately intense running, subjects performed 10 minutes of static and dynamic flexibility exercises in preparation for the exercise session. The session consisted of both resistance training and repeated sprint exercise. Resistance exercises were performed to complete failure (4 sets of 8-10 repetitions per exercise) with the eccentric phase completed in 6 seconds and the concentric phase completed as quickly as possible. The following exercises were performed: parallel back squat (free weights), leg extension and leg curl (machines), heel raises (dumbbells), and deadlifts (free weights). After the completion of all resistance exercises, subjects performed 10 sprints of 40 yards with 60 seconds rest between sprints. Subjects were instructed to complete each sprint at maximal speed. After repeated sprints, subjects performed 10 minutes of static and dynamic stretching.
Whole-Body Vibration Treatment Sessions
Subjects were randomly divided into 1 of 2 groups (WBV or stretching without WBV: FLEX). The WBV group performed 2 sessions of stretching and massage on the FreeMotion Fitness iTonic vibration platform (Figure 1) per day for 3 consecutive days. The first session was performed immediately after the exercise session with another session later the same day. Each WBV sessions consisted of 30 seconds of massage (50 Hz; amplitude, 2 mm) with the gastrocnemius, hamstring, and quadriceps muscle groups being placed on the platform (Figures 2 and 3), which was covered by a 1' foam pad. After the massage treatment, subjects stood on the platform and performed 60-second (35 Hz; amplitude, 2 mm) stretches (Figures 4-6) for the same muscle groups. Each stretch was repeated twice for a total of 6 minutes of flexibility exercise. The FLEX group performed 2 stretching sessions per day, with similar stretches being performed but without vibration stimulus.
Perceived Pain Measurement
A visual analogue scale (0, no pain to 100, maximum imaginable pain) was used to measure perceived pain. Visual analog scales have been shown to be effective for measuring perceived pain in clinical and therapeutic environments (15). Subjects were instructed to rate the pain in the legs immediately before and at 12, 24, 48, and 72 hours postworkout. To ensure subject compliance and accurate record keeping, subjects were contacted by telephone before each measurement time as a reminder to complete the visual analog measure.
Descriptive statistics were calculated for each measurement time. Analysis of variance was conducted to determine whether differences existed between groups at each measurement time. SPSS statistical software package v.14.0 (SPSS, Inc., Chicago, IL) was used for all calculations, with level of statistical significance set at p ≤ 0.05. Data are expressed as means ± SD.
Descriptive data and statistical outcomes are presented in Tables 1 and 2. Statistical analyses identified a significantly lower level of reported perceived pain at all postworkout measurement times among the WBV group (p < 0.05). No difference (p > 0.05) between groups existed at the preworkout measurement time. The degree of attenuation of pain with WBV ranged from 22-61% across the measurement times. Perceived pain peaked at 24 hours in the WBV group at 40/100, whereas the FLEX group pain peaked at 70/100 at 48 hours (Figure 7). The WBV pain levels had nearly returned to baseline at 72 hours, whereas the FLEX group pain was still significantly elevated (34/100). Thus, the trend in perceived pain demonstrated that the WBV group peaked at a much lower pain level within 24 hours of the workout, whereas the FLEX group experienced a higher amount of pain for a longer period of time.
These data demonstrate a significant and profound reduction in DOMS when WBV treatment sessions are performed in the hours and days after a strenuous exercise session among untrained individuals. Such an effect could prove valuable in aiding in the recovery process after training sessions and increasing adherence to training in the early stages of exercise adoption. Although further research is needed to identify physiologic mechanisms by which WBV may result in decreased DOMS and to verify increased adherence when WBV is included as a recovery mode, the current data clearly demonstrate a positive effect on perceived pain.
These effects could be dependent on vascular and neurophysiologic mechanisms. Enhanced local blood flow immediately after vibration training (9) is one of the factors that would be expected to result in decreased DOMS. This increase of local blood flow could increase the ability of an athlete to metabolize waste products and enhance recovery from exercise by reducing transport time of substrates (4).
Another potential mechanism may relate to the proprioceptive feedback potentiation of inhibition of pain. Vibration receptors in the skin stimulate inhibitory interneurons in the spinal cord, which in turn act to reduce the amount of pain signal transmitted from A-δ and C fibers across the midline of the spinal cord and from there to the brain (12). In their revolutionary article on pain perception in 1965, Melzack and Wall (12) proposed the gate control theory for pain perception and inhibition, mentioning vibration (page 977) as a mechanism that would “close” the pain message gate to the spinal column and brain. This mechanism would be expected to increase pain threshold (10). Therefore, it is proposed that the decrease in perceived pain by the subjects in the current study may have been caused, in part, by a raised pain tolerance because of the repeated, acute applications of WBV.
The set frequency of the WBV may also play a critical role in the decreased amount of DOMS one may experience after exercise. Frequency is critical with other modalities such as electrical stimulation with its high and low settings, in addition to the use of transcutaneous electrical nerve stimulators that are used for pain control (2). There may be a correlation in the effectiveness of WBV with regard to its frequency and effect on the nervous tissue similar to electrical current.
Whole-body vibration massage and flexibility exercises can help reduce the severity of muscle soreness after strenuous workouts among untrained individuals. Considering that muscle soreness is often reported to be a negative, and undesirable, side-effect of beginning an exercise program and completing strenuous workouts, exercise professionals can use WBV to diminish the perceived pain after such training. The inclusion of WBV is expected to significantly reduce this pain and help exercisers recover from daily workouts and can be included as an exercise supplement for increased fitness and recovery from exercise training.
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