In the last few years, the influence of neuromuscular factors and anaerobic capacity has been recognized in endurance performance (24,26). Indeed, different neuromuscular training regimens have demonstrated effectiveness for the improvement of endurance running performance (25,30,31). Subsequently, evaluation of neuromuscular parameters has become an important consideration for endurance athletes.
Endurance training has been reported to promote a faster recovery in different physiological parameters like phosphocreatine resynthesis (21), heart rate (HR) (11,13), and neuromuscular performance (14). Recently, enhanced neuromuscular performance has been reported after fatiguing running exercises in elite endurance runners (33). These authors also observed significant relationships between the enhancement of neuromuscular parameters during the fatigued state, and physical and training characteristics like maximal aerobic speed (MAS), suggesting a relationship between training background and the postactivation potentiation (PAP) observed after running exercises (33). The same phenomenon and relationships were also found in young endurance runners after an incremental running field test (10). Furthermore, this seems a typical adaptive response as a group of untrained, but physically active, young men did not experience this PAP after an incremental running field test (9). Consequently, the relationship between fatigue, endurance performance, and PAP warrants further investigation.
To date, the most useful field-based indicator of endurance training status and performance is the MAS because of its correlation with outcomes in events from 800 m to marathon (3). One of the most used and studied protocols for the determination of the MAS in the field is the “Université de Montréal Track Test” (UMTT) (20), which is a valid and easy protocol to perform. The UMTT has been studied extensively in various samples of endurance runners showing a good correlation with other performance parameters (3). Another common and simple protocol for assessment of training performance is the time limit (Tlim) at MAS, which is the maximum time spent at MAS (4). The Tlim has been associated with lactate threshold (2) and anaerobic capacity (5), and its evaluation is complementary to the MAS (1,3).
To our knowledge, there has been no comparison between the acute effects of fatigue induced by UMTT and Tlim on neuromuscular performance such as jump capacity. This would help us to understand the underlying physiological mechanisms of training status of endurance runners for training monitoring. Thus, the aim of this investigation was to study the influence of acute fatigue on jump performance after these 2 different running protocols and to examine the jump recovery profile after both protocols. It was hypothesized that an enhanced neuromuscular performance (jump capacity and recovery profile) in the fatigued condition would reflect a better running field performance.
Experimental Approach to the Problem
This study compared jump capacity in nonfatigued and fatigued conditions with running performance in distance runners. Jump capacity was determined before (nonfatigued) and at the second and seventh minute of recovery after (fatigued) both the UMTT and the Tlim at MAS.
Twelve male athletes volunteered for this study (age = 23.2 ± 3.3 years; height = 175.6 ± 5.8 cm; mass = 65.2 ± 6.7 kg). All participants had been training and competing in distance running events for at least 2 consecutive years. Their training status ranged from regional to elite with their best records for the 1500 m (3 minutes 42 seconds to 4 minutes) and 3000 m (8 minutes 18 seconds to 8 minutes 47 seconds), similar to but 11 and 16% slower than current world records, respectively. All participants were informed of and familiar with all procedures such as the UMTT and Tlim and provided informed written consent in accordance with the Declaration of Helsinki.
Participation involved the conduction of and recording of performance during the UMTT and Tlim with protocols separated by 48 hours to 7 days. In addition, jump capacity was determined before and after the UMTT and Tlim protocols. The study was conducted at the end of the season within 1 and 2 weeks after the last running competitive event by participants. For the purposes of this study, participants were advised to maintain low-intensity training (running at an intensity lower than 80% of maximum HR (HRmax) and active recovery participating in recreational activities interspersed with some resting days ad libitum) in the tapering 7-15 days before the experiment. Participants were also advised to avoid caffeine drinks and any food ingestion in the 2 hours before the testing sessions.
For both the UMTT and the Tlim protocols, participants arrived at a 400-m outdoor track between 6 and 8 pm. The environmental conditions were temperature of between 22 and 24° C, relative air humidity of 60-80%, and mean air velocity less than 2 m·s−1. First, participants completed a warm-up consisting of a running trial on the grass at an intensity of 60% estimated HRmax (220-age) followed by 2-3 practice countermovement jumps (CMJs). After the warm-up, participants performed 2 CMJs with at least 15 seconds between attempts. The maximum height of the 2 CMJ attempts was determined as the jump performance during nonfatigued conditions (CMJB). The jump height (H) was calculated from the following formula: H = t2·g·8−1(m), where g is the acceleration due to gravity and t is the time in the air. The time between the push-off and landing phases of the CMJ was registered with a contact mat (7), and the formula was calculated according to manufacturer's instructions (Ergojump, Bosco System, Rome, Italy). When the baseline CMJ was finished, participants drank isotonic fluids (Aquarius, Begano SA, Spain) ad libitum before the start of the running protocols to avoid a possible risk of dehydration or hyperthermia.
The UMTT was conducted in line with the original protocol (20) (1·km·h−1 increments each stage of 2 minutes until exhaustion) but the pace was imposed by a cyclist with a velocimeter. Before starting the UMTT, the velocimeter was calibrated in accordance with manufacturer's guidelines (SC6501; Shimano, Taiwan). The velocity of the final stage completed of the UMTT was recorded as the MAS. Based upon prior consultation (Léger, PhD, oral communication, May 1999), 0.5 km·h−1 was added to the MAS if participants completed only 1 minute of the final stage. All participants were encouraged to undertake the UMTT until volitional exhaustion, as determined by rating of perceived exertion (RPE) >19.
The protocol of the Tlim was as described previously (4) and consisted of a constant running pace at the MAS, as determined during the previous experimental testing session in the UMTT. All pretest procedures were identical to the UMTT testing day including the use of the same running clothes and shoes. All athletes were encouraged to do their best until they were exhausted. The test finished when the athlete could not maintain the constant running velocity, achieving volitional exhaustion, and a reported RPE > 19.
The HR exhibited during and after the UMTT and Tlim exercises was recorded with a HR monitor (×625; Polar Electro, Kempele, Finland) with a 5 second interval sampling rate. The HRmax was defined as the maximum value recorded at the end of each running protocol. At the cessation of the UMTT and Tlim protocols, a chronometer was started with participants allowed to walk to the starting point during recovery. During this walk, a blood sample was collected from the fingertip within the first, minute to determine the final blood lactate level (LA) with a portable lactate analyzer (Lactate Scout; Senslab, Leipzig, Germany).
At the second and seventh minute of recovery, participants performed 2 CMJ attempts, as described above, for the evaluation of jump performance during fatigued conditions (CMJ2 and CMJ7). In addition, the net increments in jump height between the CMJ during nonfatigued and fatigued conditions (CMJ2 − CMJB = ΔCMJ2; CMJ7 − CMJB = ΔCMJ7) were determined.
Data were expressed as statistical descriptives (mean ± SD or range). For assessment of reliability of jumping attempts, intraclass correlation coefficients (ICCs) were employed. For comparison of mean values, paired Student's t-tests were performed. Pearson product moment correlation coefficient (r) was used to determine the relationship between selected parameters. Statistical significance was set at 0.05. All data were analyzed using SPSS 12.0 statistical software (SPSS, Inc., Chicago, IL).
The results relative to running exercise performances are shown in Table 1. There was no difference between protocols for LA (LAUMTT = 11.82 ± 2.02 mmol·L−1 vs. LATlim = 12.01 ± 1.94 mmol·L−1; p > 0.05), whereas HRmax was significantly greater after the UMTT compared with the Tlim (189.4 ± 8.4 b·min−1 vs. 185.1 ± 7.3 b·min−1; p = 0.004).
Graphical profile of jumping performance after the UMTT and the Tlim protocols are shown in Figures 1 and 2, respectively. Comparative graphical profile after both protocols is shown in Figure 3. Jump attempts demonstrated a good reliability as indicated by ICC (Table 2). Individual jump scores in nonfatigued (CMJB) and fatigued condition (CMJ2) in the UMTT testing day are shown in Figure 4.
In the nonfatigued state, jump performance was significantly greater before the Tlim compared with the UMTT (Figure 3). Jump performance was enhanced during the fatigued conditions with jump height greater at the second minute of recovery after both protocols but only greater at the seventh minute after the UMTT (Figures 1 and 2).
There were no significant correlations between running and jumping performance parameters. Correlations were detected between the baseline jumping performance before the UMTT and Tlim protocols with the improvement jump performance at the second minute after the Tlim test (CMJBUMTT − ΔCMJ2Tlim; r = 0.802; p = 0.002; CMJBTlim − ΔCMJ2Tlim; r = 0.713; p = 0.009).
The major finding of this study was the PAP observed in jump capacity, after the UMTT and the Tlim tests at the second minute of recovery. This is the first time, to our knowledge, that PAP has been demonstrated in distance runners in the field. These findings are in agreement with those previously reported in laboratory (32) and in the field for a group of young endurance runners (10).
This phenomenon of PAP is opposite to the observed force loss after fatiguing running exercises of large duration (12,19,22-24,27). Previously, some authors (33) have reported an enhancement in jump capacity and power of the lower limbs in a group of well-trained runners in laboratory immediately after an incremental test to determine MAS, a tempo running protocol (40 minutes at 80% MAS), and an interval running protocol (40 minutes at 100% MAS, 2 minutes of work, and 2 minutes of rest). Moreover, others have reported a potentiation in twitch torque at 10 minutes after an anaerobic interval workload (5 × 300 m at 77% of top velocity) (29) and after a constant running (6 km at anaerobic threshold) (28) in well-trained runners. This apparent controversy could be due to the heterogeneity in neuromuscular evaluation methods (power tasks, twitch torque), running fatigue exercises performed (long duration, interval, and incremental running), and time of recovery until neuromuscular evaluation (immediately after 10 minutes or hours).
In our case, CMJ was selected because it is a more natural task and easier to perform in the field. We conducted the first fatigued CMJ attempt at the second minute of recovery because the starting point for fatigue was guaranteed in a homogeneous condition for all subjects because the end point of the track running tests may be uncertain. Indeed, it was expected that a full recovery of the fast component of phosphocreatine resynthesis would be achieved by the second minute of recovery in endurance-trained runners (21).
It is difficult to identify the physiological basis for the PAP after fatiguing exercise. Previously (33), it has been suggested that the increased height in the CMJ could be the result of an increased utilization of elastic energy. Other authors (8) found an increased elastic energy in the fatigued condition, but with an impairment of explosive force. These authors suggested that the effect of fatigue allows fast-twitch-type muscle fibers to reuse greater amounts of stored elastic energy than slow-twitch ones during stretch-shortening cycle exercises performed with slow stretching speed and large stretching length (8). We could speculate that improved CMJ in the current study resulted from an elastic energy enhancement counteracting the force loss. In this regard, it is expected that the force loss in the fatigued state for endurance athletes may be smaller compared with power athletes (14,32).
The second major finding of this study was the different recovery profile after 2 running protocols in CMJ performance at the second and seventh minute of recovery. A more enhanced maintenance of PAP was observed after the UMTT than after Tlim. A possible explanation could be the different physiological strain of the 2 running exercises (16,17), reflected by the significantly different HRmax between protocols. On the other hand, the similar high LAs observed after both protocols reflected a similar metabolic activation. Therefore, these results may indicate that the mean acidosis level did not influence PAP. Regarding this, previous work (33) has reported a correlation between LAs and jump enhancement (33). Others (29) have also reported a potentiation effect despite the high-lactate concentration. In both cases, LAs after the incremental running and the anaerobic interval workload were similar to the ones measured in our study after both protocols.
In contrast to the work performed in the laboratory (33) and the previous work in the field (10), no correlation between jump and endurance performance parameters was exhibited in the current study. Because the participants were in the tapering phase after the competitive season (July and early August), we could speculate about the influence of the season's stage and their fitness level. In this regard, the study of Vuorimaa et al. (33) was also performed at the end of the competitive season (September and early October), and similar results were observed in a precompetitive season evaluation (May) (Vuorimaa, PhD, written communication, January 2008). Therefore, the phase of the season may not be an important factor, and other physical parameters could influence the PAP. The absence of correlations between jump parameters and the MAS obtained from the UMTT is contrary with previous results in the study with young endurance runners (10). On the other hand, we found correlations between CMJB and height increments in fatigued condition after Tlim. Similar correlations were exhibited in a previous work with the relationship direction dependent on the running exercise (maximal running and interval running) (33). Therefore, the better the baseline jump capacity, the better the CMJ enhancement after the Tlim. One possible explanation is that the athletes with the highest proportion of fast-twitch fibers demonstrate a greater PAP in the fatigue condition. Reported greater PAP in endurance-trained subjects with an increased content of fast myosin light chains in Type I fibers (15), and higher jump capacity in subjects with the highest proportion of fast-twitch fibers (6), provide further support for this possible explanation.
One possible limitation of our study is the small but significant difference in CMJB between protocols (p < 0.005). In this regard, the high ICC values reflect a great stability of CMJ performance. This small difference could be attributable to biological variability, although we recorded performances separated by 48 hours to 7 days.
In summary, endurance athletes experienced a PAP after 2 different running protocols with the PAP profile, protocol dependent. Contrary to previous studies, we did not find correlations between neuromuscular and endurance performance parameters with the mechanism for PAP yet to be determined.
Base upon the current results, we suggest that jump capacity be evaluated in the fatigued condition to explore athlete's fitness level along the season. Furthermore, we suggest that neuromuscular training be performed after running exercises (i.e., plyometrics after interval training), in a similar fashion to that of other modalities that take advantage of PAP, such as the so-called complex training (18).
This study is supported in part by Consejo Superior de Deportes grant (12/UPB31/06). We also want to fully recognize the contribution of Anthony S. Leicht in the revision of the article.
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