Introduction
The accurate assessment of the maximum strength is of great relevance in determining both the functional capacity and the exercise training load for individuals of different training status and ages. In this regard, the one repetition maximum (1RM) test is the most common measure of the maximum dynamic strength (9). There are several factors, however, that can affect the precision of a 1RM assessment. Among these factors, the warm-up procedure (e.g., aerobic exercise, specific activity, and stretching) seems to influence the 1RM test results (6,7,11,12,20–22,24).
It has been generally recommended that the warm-up routine preceding a 1RM testing should comprise both general (aerobic) and specific exercises (mimicking the target activity) (2,4,9). The general warm-up (GWU) exercise is designed to increase body temperature, whereas the specific warm-up exercise attempts to increase neuromuscular activation (7,15,21,25).
Regarding the GWU, low-intensity and short-duration aerobic exercises have been traditionally recommended before 1RM testing (i.e., running for 5 minutes at 9 km·h−1(9)). However, there is little scientific evidence supporting such suggestion. Furthermore, it has been demonstrated that body temperature should be increased around 3°C to trigger performance enhancing benefits (5,10–13,23), and that this elevation seems to depend on both the intensity and the duration of the GWU (18). Moderate-intensity (i.e., 60–70% V[Combining Dot Above]O2max) aerobic exercise may increase the rate of body temperature elevation (16,19), suggesting GWU efficacy might be augmented. However, moderate-intensity activity may also lead to a higher level of fatigue impairing performance (7). Thus, it is conceivable that both variables should be controlled when designing warm-up routines.
Abad et al. (1) have demonstrated that cycling for 20 minutes at 60% of the predicted maximum heart rate (HR), followed by specific warm-up, improved leg press 1RM performance by ∼8% when compared with a no-GWU condition. The exercise intensity in the Abad et al. (1) work is within the range suggested by Bishop (7) (40–60% V[Combining Dot Above]O2max) to improve performance in short-term activities. Yet, the duration was based on previous studies that showed that muscle temperature raises ∼3°C in approximately 15–20 minutes of aerobic exercising (9). Thus, it seems plausible to suggest that a long-duration and low-intensity GWU can improve performance to a larger extent than the recommended short-duration and low-intensity GWU protocol. Nevertheless, data comparing distinct GWU durations and intensities are still lacking.
Therefore, the purpose of this study was to compare leg press 1RM performance after different GWU protocols. According to previous results from Abad et al. (1) and Bishop's suggestions (7), we hypothesized that a low-intensity long-duration GWU will be more effective in improving maximal dynamic strength.
Methods
Experimental Approach to the Problem
This was a crossover design study for testing the effect of different GWU protocols on lower-limb 1RM performance. Subjects were tested in 5 different conditions. In 4 of these conditions, the subjects performed the combination of different durations (i.e., 5 and 15 minutes) and intensities (i.e., 40 and 70% V[Combining Dot Above]O2max) of aerobic exercise. After the completion of the GWU, the subjects rested for 3 minutes and then performed the specific warm-up protocol, standardized for all conditions. In the remaining condition, which served as a control (CTRL), participants performed only the specific warm-up.
Subjects
Sixteen strength-trained male students majoring in physical education (age: 24.9 ± 3.2 years; body mass: 76.7 ± 8.2 kg; and height: 176.3 ± 8.0 cm) volunteered to participate in this study. The subjects had at least 12 months of strength training experience (15.5 ± 3.1 months) and performed the inclined (45°) leg press exercise during their regular training routine at least twice a week. They were free from any lower extremity injuries and neuromuscular disorders. The investigation was approved by an institutional review board for use of human subjects, and all of the participants signed an informed consent form before participation.
Pretesting Sessions
Before undertaking any of the GWU conditions, participants performed a maximal incremental test on a cycle ergometer to determine their maximum aerobic capacity. Then, they performed 2 familiarization sessions with the lower-limb 1RM test using a leg press machine (Resistance NKR; Nakagym, São Paulo, Brazil). During the familiarization sessions, individual leg press machine settings were recorded for reproduction throughout the study. Each repetition started with the knees fully extended, and then, the participants flexed their knees to reach 90° of flexion (end of eccentric phase) before extension (concentric phase). After adjustments in the machine, the participants warmed-up on the stationary bicycle for 5 minutes at a self-selected pace and performed a simulated 1RM test to obtain an estimation of the load to be used during the experimental sessions.
Procedures
Maximal Incremental Exercise Test
Participants laid down for 10 minutes before the test to assess resting HR and blood lactate concentration [La−]. The maximal incremental exercise test was carried out on a cycle ergometer (Ergo-Fit 167; Ergo-Fit, São Paulo, Brazil). Seat height was adjusted individually allowing near full knee extension during each pedal revolution. Oxygen uptake (V[Combining Dot Above]O2) was measured breath-by-breath throughout the test using a gas analyzer (Quark b2; Cosmed, Rome, Italy) and averaged over 30-second intervals. The gas analyzer was calibrated according to manufacturer instructions using ambient air, a gas of known composition containing 16.0% O2 and 5% CO2, and a 3-L syringe. The HR was assessed during the test with a HR monitor (S810i; Polar Electro Oy, Kempele, Finland) synchronized with the gas analyzer. The ratings of perceived exertion (RPE) was also assessed during and immediately after the test (8). Blood samples (25 μl) were collected from the left ear lobe immediately, 1, 3, and 5 minutes after the exercise test for [La−] determination, using an automatic blood lactate analyzer (1500 Sport; Yellow Springs Instruments, Yellow Springs, OH, USA).
After a 3-minute warm-up at 50 W, participants cycled at a pedal frequency of 60 rpm with increasing workload increments of 30 W·min−1 until voluntary exhaustion (the inability to sustain a minimum pedal cadence of 50 rpm). Participants received strong verbal encouragement to continue as long as possible. V[Combining Dot Above]O2max was determined when 2 or more of the following criteria were met: an increase in V[Combining Dot Above]O2 of less than 2.1 ml·kg−1·min−1 on 2 consecutive stages, a respiratory exchange ratio ≥1.1, and ±10 b·min−1 of the maximal age-predicted HR. The maximal HR (HRmax) was defined as the highest value obtained during the last stage of the test.
Testing Sessions
Participants were tested for their 1RM in 5 different occasions, 4 different GWU conditions, and 1 CTRL condition (no-GWU). Before and immediately after each GWU, we assessed HR, [La−], and RPE. Testing sessions were performed in a randomized order at least 72 hours apart, at the same time of the day (i.e., between 2 and 4 PM). Participants were asked to refrain from any physical activity for 48 hours before testing.
General Warm-up Conditions
General warm-up was performed on the same cycle ergometer used for the maximal incremental test. Participants were tested for their 1RM after 4 different GWU and a CTRL condition. During CTRL, participants did not perform aerobic exercises before the specific warm-up. The 4 GWU conditions were determined based on different combinations of 2 intensities (low, 40% V[Combining Dot Above]O2max; moderate, 70% V[Combining Dot Above]O2max) and 2 durations of aerobic exercise (short, 5 minutes; long, 15 minutes). Therefore, the combinations were as follows: (a) short duration and low intensity (SDLI: 5 minutes at 40% V[Combining Dot Above]O2max); (b) short duration and moderate intensity (SDMI: 5 minutes at 70% V[Combining Dot Above]O2max); (c) long duration and low intensity (LDLI: 15 minutes at 40% V[Combining Dot Above]O2max); (d) long duration and moderate intensity (LDMI: 15 minutes at 70% V[Combining Dot Above]O2max). Also, we instructed the participants to perform only light stretching exercises (i.e., short-duration submaximal stretching) during the warm-up because extensive stretching exercises can negatively affect strength performance (3,14).
1RM Test
All the participants performed the leg press 1RM test after the CTRL (no-GWU) and each of the 4 experimental conditions previously described. Three minutes after the GWU protocol, participants performed a specific warm-up, comprising 1 set of 8 repetitions and 1 set of 3 repetitions at 50 and 70% of the familiarization session leg press 1RM values, respectively, separated by a 2-minute interval. After the completion of the specific warm-up, participants rested for 3 minutes. Then, they had up to 5 attempts to obtain the 1RM value. A 3-minute rest interval was granted between attempts (9). Tests were conducted by 2 experienced researchers, and strong verbal encouragement was provided during the lifts.
Statistical Analyses
Results of the 1RM test after each GWU protocol are presented as means (±SD). After normality assurance (Shapiro-Wilk test), HR, RPE, and [La−] from each GWU protocol was compared using a mixed-model analysis. GWU conditions were set as fixed factor and subjects as a random factor. Whenever a significant F-value was obtained, a Tukey post hoc test was performed for multiple comparison purposes. Significance level was set at p ≤ 0.05.
Results
Participants presented a V[Combining Dot Above]O2max of 39.5 ± 1.5 (ml·O2·kg−1·min−1). The RPE, HR, and [La−] were not significantly different at rest (p = 0.99) between conditions (data not shown) and were elevated after GWU in SDLI (p < 0.001), SDMI (p < 0.001), LDLI (p < 0.001), and LDMI (p < 0.001) (Table 1). Participants rated their RPE after LDMI the highest among GWU conditions. Furthermore, RPE during the SDMI was higher than during the LDLI (p = 0.01) and SDLI (p = 0.01) conditions. Heart rate and [La−] presented the same response pattern as RPE.
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Table 1: Mean ± SD values for RPE, HR, and [La−] after each condition.*
Leg press 1RM values were higher (p < 0.01) after LDLI when compared with the other 3 GWU protocols and the CTRL condition (Figure 1). The 1RM values after the LDMI were significantly lower than those from the GWU protocols and CTRL (p < 0.01) (Figure 1). There were no differences in 1RM between the SDMI, the SDLI, and the CTRL conditions (p = 0.99).
Figure 1: Mean (SD) leg press 1RM values for each GWU condition *p ≤ 0.05 compared with CTRL, SDMI, SDLI, and LDLI, †p ≤ 0.05 compared with CTRL, SDMI, SDLI, and LDMI.
Discussion
The purpose of this study was to compare the effects of different GWU intensities (40 and 70% V[Combining Dot Above]O2max) and durations (5 and 15 minutes) on 1RM leg press performance. The LDMI condition significantly decreased the leg press 1RM values compared with the other conditions. This was possibly because of greater fatigue development as observed by higher RPE, HR, and [La−] values (Table 1). The LDLI condition produced significantly higher leg press 1RM values than the other GWU conditions while producing just small increments in the variables associated with the physiological stress (Table 1). It is interesting to notice that both the RPE and the HR values observed after LDMI were >30% higher than those after LDLI (Table 1). Furthermore, [La−] values were almost 3 times higher after LDMI when compared with LDLI (Table 1). These differences indicate the greater physiological stress associated with LDMI, ultimately leading to muscle fatigue that may, at least partially, explain the decrease in 1RM values (7).
Accordingly, Bishop (7) stated that before a short-term activity such as the 1RM test, the warm-up procedure should appropriately increase body temperature while minimizing deleterious effects of fatigue. Although it is known that the duration and the intensity of exercise affect temperature elevation and fatigue development, which can negatively impact strength performance, this is the first study to investigate the effects of different GWU durations and intensities on 1RM performance.
Traditionally, testing guidelines (2,4,9) recommend a GWU of 5- to 10-minute duration before strength testing. However, previous studies have demonstrated a significant increase in muscle temperature only after 15–20 minutes of moderate-intensity aerobic activity (11,12,18,23). In addition, there are suggestions that performance is only positively affected if temperature is raised around 3°C. Although we did not measure muscle temperature, it is tempting to speculate that SDLI and SDMI did not raise muscle temperature properly to trigger temperature-related performance enhancing benefits. Thus, it is possible to suggest that GWU duration should last for at least 15 minutes.
Nonetheless, caution should be exercised when considering the intensity of the GWU. The results reported herein suggest that if a GWU is of short duration (i.e., 5 minutes), intensity does not affect strength performance. However, according to our results, the combination of long duration and moderate intensity (LDMI) actually impaired performance. Thus, it is conceivable that long durations should be recommended only when combined with lower exercise intensities to avoid fatigue development.
Our data support these suggestions as the LDLI condition produced the highest leg press 1RM values while maintaining the second lowest physiological stress among the 4 GWU conditions. We assessed RPE, HR, and [La−] to obtain an estimation of the physiological stress produced by the warm-up activities. These data allow us to suggest that the physiological stress induced by the warm-up activity should be low. Heart rate of approximately 55% of HRmax, RPE around 10-point in Borg scale (very light exercise) and low [La−] were associated with the condition that elicited the greater 1RM value, LDLI. Although SDLI induced lower physiological stress compared with LDLI, it is possible that duration was insufficient to induce the appropriate temperature elevation to trigger performance enhancing benefits. However, these assumptions are limited to the duration and intensities tested.
Strength testing guidelines (2,4,9) recommendations for the GWU have little scientific support. In fact, recommended durations (5–10 minutes) seem to be shorter than necessary (15–20 minutes) to produce performance enhancing benefits. Furthermore, intensity recommendations are unclear, but the results presented here in association with those of Abad et al. support the notion that HR should be around 55–60% of HRmax if the exercise is performed for 15–20 minutes. Collectively, our data suggest the adoption of low-intensity (40% V[Combining Dot Above]O2max) but longer duration (15 minutes) warm-up than previously proposed. In fact, the increase in 1RM observed in the LDLI warm-up protocol (3–4%), albeit may be considered small, is similar to those observed in response to long-term strength training in previously strength-trained individuals (17), thus constituting a meaningful difference in any testing environment. Despite the aforementioned, these data cannot be extrapolated to other populations as only strength-trained men were studied.
Importantly, one cannot rule out the possibility that the time lag between completing the warm-up and the last 1RM attempts test was excessive, thus hindering the increased temperature-induced benefits on performance. Unfortunately we were unable to assess body temperature, which is an important limitation of the present study. Nevertheless, such limitation is partially mitigated by the fact that maximum dynamic strength testing requires trials up to failure interposed with long intervals (2,4,9).
In summary, our data indicate that longer (i.e., 15 minutes) than recommended (5–10 minutes) GWU at a low intensity (i.e., 40% V[Combining Dot Above]O2max) improves maximum strength testing performance.
Practical Applications
Maximal strength testing is commonly used for both training prescription and monitoring. According to our data, performing a 15-minute low-intensity (40%V[Combining Dot Above]O2max) aerobic exercise before a maximum strength assessment is recommended to improve performance. The results of the present study are important for strength testing in both practical and research environments. Although the difference in 1RM performance between different GWU conditions may be misinterpreted as small (3–4%), it is meaningful in any testing environment. Moreover, in well-trained subjects, this difference might mean the result of weeks of heavy strength training.
However, this recommendation is still limited to maximum strength tests (i.e., 1RM), and should not be applied to other strength tests (i.e., power or muscle endurance tests).
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