The current study indicates that the aerobic warm-up prior to resistance exercise to some extent prevents muscle soreness at the central muscle belly. A significant group by time interaction was observed for the overall PPT (PPTcental+distal) as well as for PPT at the mid-belly (PPTcentral) of rectus femoris, indicating that these measures of PPT changed differently with time in the three groups. In contrast to within the control group, no significant reduction was observed in PPTcentral+distal or PPTcentral within the warm-up group from baseline to 24 hours (day 2) or 48 hours post-exercise (day 3). The reduction of PPT was substantially larger for the control group than for the warm-up group, especially for PPTcentral (~20–25% reduction in the control group versus ~3–5% reduction in the warm-up group). Moreover, PPTcentral was significantly higher for the warm-up group than the cool-down group on day 2 and also tended to be higher on day 3. This may indicate that aerobic warm-up exercise is more effective in preventing muscle soreness the first 24 hours compared to aerobic cool-down exercise. However, the finding of less reduction of PPT in the experimental groups compared to the control group was not reflected by the subjective VAS ratings of perceived pain in the anterior thigh muscles. Both experimental groups and the control group reported higher VAS ratings on day 2 and day 3 compared to day 1 but VAS ratings did not differ between groups.
Moderate intensity cycling was chosen as warm-up and cool-down exercise for several reasons. First, cycling activates large muscle groups that leads to a relatively steep rise in muscle temperature that reaches a plateau after 10–20 min (Saltin et al., 1968
). Increased muscle temperature may increase muscle extensibility (Noonan et al., 1993
), thereby reducing the risk of muscle damage from overstretched muscle fibers. Second, cycling mainly constitutes concentric muscle work (Ettema and Loras, 2009
). Other common types of exercise that activate the leg muscles such as jogging/running induce eccentric tension of the leg extensor muscles when the downward motion is decelerated after the foot touches the ground. This eccentric activation may result in muscle damage (Armstrong et al., 1983
). Exercise that mainly constitutes concentric muscle contractions may therefore be a better choice for the warm-up and cool-down before and after leg resistance exercise to avoid aggravation of muscle damage by additional eccentric contractions. This may be particularly relevant for the cool-down exercise and there is some evidence indicating that concentric cool-down exercise performed in water results in enhanced recovery of flexibility of the leg muscles compared to jogging (Takahashi et al., 2000
Similar to our findings, previous studies have indicated that warm-up exercise prior to eccentric exercise is associated with less reduction of PPT in lower (Law and Herbert, 2007
) and upper limb muscles (Ingham et al., 2010
). One study included cool-down exercise but found no effect on PPT after eccentric exercise (Law and Herbert, 2007
). However, none of these studies investigated whether warm-up or cool-down exercise had a different effect on PPT at different intramuscular regions. A non-uniform distribution of PPT along the rectus femoris after eccentric exercise has been reported in previous studies (Baker et al., 1997
; Hedayatpour et al., 2008
). However, while Baker et al. (1997)
found the largest reduction in PPT at the central region, Hedayatpour et al. (2008)
found it at the distal region. The reason for these contrasting findings is unclear but may relate to different protocols for inducing DOMS, i.e., downhill running (Baker et al., 1997
) versus leg exercise in a dynamometer (Hedayatpour et al., 2008
). In our study, the similar relative reduction of PPT at the distal and central regions within the control group (i.e., ~20–30% at both sites) may indicate that the muscle damage was of similar magnitude in both regions. Thus, the site-specific differences in PPT between the control group and the experimental groups at day 2 and day 3 are likely caused by site-specific responses to the intervention.
A possible explanation for the differential effect at the central and distal muscle region may relate to a graded vascularization throughout the muscle belly. Compared to the mid-belly of quadriceps a higher density of fast-twitch fibers was found in the distal region of this muscle (Travnik et al., 1995
). Fast-twitch fibers have less capillary-to-fiber ratio than slow-twitch fibers (Sjøgaard, 1982
) and muscle regions with relatively high density of fast-twitch fibers may therefore have a less advantageous effect of aerobic warm-up and cool-down exercise. This notion is partly supported by a study showing less muscle oxygenation in the distal versus central muscle region in vastus lateralis during exercise (Kennedy et al., 2006
). Moreover, fast-twitch fibers may be more susceptible to damage following eccentric exercise compared to slow-twitch fibers (Takekura et al., 2001
). It should also be noted that the warm-up and cool-down exercise in the current study was performed with low force concentric muscle work that will mainly activate slow-twitch fibers. Thus, our findings may suggest that the preventive effect of moderate intensity warm-up and cool-down exercise on hyperalgesia is more pronounced in muscle regions or muscles that are well vascularized with high density of slow-twitch fibers. However, this notion lacks empirical support and needs to be confirmed in future studies.
Although the average VAS ratings of muscle soreness in the anterior thigh muscles were more than threefold higher in the control group than in the warm-up group on both day 2 and day 3, the difference did not reach significance due to the large inter-individual variation in pain scores. In this study, the participants were instructed to rate muscle soreness during walking a short distance at preferred speed and the pain scores were quite low. Typically, the perceived muscle pain associated with DOMS is more intense during forceful contractions of the affected muscle. It is therefore possible that the difference between the control group and the experimental groups would have been more distinct if VAS ratings were obtained during more forceful contractions of the quadriceps muscle. Moreover, the lack of difference between the control group and the experimental groups may be due to the convergence of nociceptive input from other regions of the quadriceps muscle to the dorsal horn of the spinal cord (Kosek and Hansson, 2003
). Thus, the perceived muscle pain is likely to be dominated by the most intensive input (i.e., similar mechanism as for referred pain), which in this case could originate from any part of the anterior thigh muscles.
A prolonged force decline after eccentric exercise is considered a valid and reliable indirect marker of muscle damage (Warren et al., 1999
). Previous studies have provided contradictory results regarding the preventive effect of the warm-up or cool-down on force decline (Gulick et al., 1996
; Ingham et al., 2010
; Takahashi et al., 2006
). However, the exercise protocols vary considerably between different studies and none of them investigated the effect of aerobic warm-up or cool-down exercise. We observed a tendency for a more pronounced force decline in the control group (~20% decline, day 2 and 3) compared to both experimental groups (~10–12% decline, day 2 and 3); however, due to our limited sample size these differences did not reach significance. Thus, based on the mixed results in our and previous studies, it is difficult to draw any firm conclusion regarding the effect of aerobic warm-up and cool-down exercise on force decline after eccentric exercise.
There are several strengths of our study, such as the comparison of randomized groups, no withdrawals or missing data, and the outcome variables specified a priori
. PPTs were recorded by a force transducer algometer which is a well-established and highly reliable method for measurement of hyperalgesia (Jones et al., 2007
). Likewise, recordings of acute pain by VAS (Bijur et al., 2001
) and recordings of isometric knee extension force have been shown to be highly reliable (Sole et al., 2007
). Moreover, we used an identical protocol for the warm-up and cool-down exercise which enabled a direct comparison of the effect of these two exercise modalities on DOMS following resistance exercise. However, it is possible that the warm-up and cool-down have an additive effect on prevention of DOMS and this should be investigated in future studies. Previous experience with physical exercise and leg strength may also influence on the effect of warm-up and cool-down exercise. Although no data is available for women, leg strength of our male participants corresponded well with leg extension torque recorded in other studies of young healthy male adults. The converted torque values for our male subjects (n=15; 222 ± 25.3 Nm) were in agreement with the knee extension torque of 231 ± 9 Nm reported by Thorstensson et al. (1976)
and the 10th (~160 Nm) and 90th (~275 Nm) percentile reported by Alangari and Al-Hazzaa (2004)
. None of our participants was competing at the national or international level, but all participated in recreational physical activity on a regular basis. Whether our findings can be generalized to individuals with either higher or lower physical capacity, e.g., elite athletes or patients groups, remains uncertain. It should also be noted that PPT was only recorded from the rectus femoris muscle and we cannot conclude whether the warm-up and cool-down have a general effect on the quadriceps muscle. Finally, a longer follow-up period until all variables returned to baseline would have enabled a more thorough characterization of the recovery pattern.
In conclusion, it may be stated that the present study indicates that aerobic warm-up exercise of moderate intensity with mainly concentric muscle work performed prior to intensive leg resistance exercise may prevent muscle soreness but not loss of muscle force. The preventive effect on muscle soreness is most pronounced at the central muscle region. Cool-down exercise may be less effective than the warm-up in attenuating muscle soreness the first 24 hours after resistance exercise. The practical implication is that moderate aerobic warm-up or cool-down exercise, with mainly concentric muscle work, can be recommended to attenuate muscle soreness following intensive leg resistance exercise.