Athletes have always tried methods and devices that will give them an advantage in competition. The external nasal dilator (END) has remained very popular over the past few years as a means of enhancing athletic performance in a variety of sports. Based on the findings of a single study (12), it has been suggested that “nasal strips can help an athlete do the same amount of exercise using less energy” (8). The rationale is that if airway resistance is reduced, then respiration is easier; thus, the metabolic cost of ventilation is lower. Unfortunately, despite their continuing and extensive use by athletes in a variety of sports, the efficacy of ENDs in improving athletic performance has yet to be unequivocally demonstrated.
The END is placed across the bridge of the nose and is secured by means of adhesive on one side of the device. Embedded within the device are two plastic strips that apply 20-25 g of outward pull on the nostrils and increase the dimensions of the nasal airway passages (1,18). Despite variability in the results, several studies have demonstrated an overall decrease in the resistance to airflow during nasal breathing and increased inspiratory volume (9,15,21,29). The importance of this finding was articulated by Gehring et al. (11), who speculated that the increased inspiratory volume during nasal breathing could theoretically translate into energetic advantage during sports. The same group cautiously concluded that ENDs caused a small delay in the switch from nasal to oronasal breathing, but the authors warned against interpreting any measurable effect of ENDs on performance without further investigation (23).
O'Kroy (18) and Chinevere et al. (7) reported no differences in maximal oxygen uptake or any other ventilatory parameter with and without the use of END. In their study on the work of breathing, O'Kroy et al. (19) found that oronasal breathing with the END did not reduce the work of the respiratory muscles. Other studies have also found no differences in aerobic parameters between the experimental and placebo (2) or between experimental and control conditions (28). The END was also shown not to have any effect on anaerobic power during the Wingate anaerobic power test (26) or rate of perceived exertion (RPE) (22), or on cardiorespiratory indices during recovery from intense exercise (27). Bourdin et al. (3) demonstrated that ENDs had no effect on heart rate and performance during high-intensity exercise on the field in trained individuals. Collectively, these studies establish that ENDs are successful in increasing nasal passages and decreasing nasal airway resistance (33), but this change does not translate into improved measures of physical fitness (5,7).
The aforementioned studies used a variety of experimental protocols with quick progression of increasing intensity, aiming at examining the potential for conclusive evaluation of the role of ENDs during intense or even maximal exercise. However, if the END plays an important role in energy production during prolonged exercise, then intensity at o2max should not be the point of comparison, as maintaining such a high level is difficult even for seasoned athletes. Alternatively, Smith and Jones (25) argue in favor of the use of a maximal lactate steady state (MLSS), the intensity above which lactate accumulates in the blood. Bourdin et al. (3) used that justification for their field running study on the effectiveness of ENDs, but they established the individual intensities based on a 4 mmol·l−1 lactate threshold (LT), without allowing for variations among the participants. Thus, despite the abundance of work on this area, the effects of ENDs on the individual LT have yet to be clearly demonstrated.
An additional component not examined previously in the context of ENDs is the role of physical conditioning in metabolism. It has been well established that physical training improves pulmonary ventilation, an adaptation necessary for the increased energy consumption by the working muscles. If, as Boutellier and Piwko (4) indicate, ventilation is a limiting factor in endurance tests in sedentary subjects, then perhaps the use of END may improve oxygen delivery to the working muscles in this population. Therefore, the purpose of this study was to compare the effects of END on the LT on sedentary and aerobically trained women. To our knowledge, no study has examined the potential effects of ENDs exclusively among women. Based on available literature on male participants, it was hypothesized that the END would have no effect on the individual LT.
Experimental Approach to the Problem
A randomized, counter balanced, crossover experimental protocol was used in this study. Each participant performed two tests, one with the END and one without the END. Blood samples were collected at identical time intervals in both tests, and the lactate threshold (LT) was determined for each exercise bout. The LT values were subsequently compared using a paired t-test.
Nine sedentary female college-age students (age 19 ± 1.0 y) who had not participated in any type of regular exercise or recreational activity for more than 6 months, eight preseason cross-country female college athletes (age 20 ± 2.3 y) who exercised two to three times weekly at moderate intensity, and six in-season female college crew athletes (age 20 ± 1.7 y) volunteered to participate in this study. These groups were selected in an attempt to identify potential effects of conditioning on the effects of the END on blood lactate response to exercise. It was hypothesized that the three groups would yield different levels of blood lactate during exercise. None of the participants had used the END before this study. All volunteers were non-smokers, were free of respiratory disease and allergies, and were instructed to refrain from strenuous exercise for at least 24 hours before each of the testing sessions. All methods and procedures were approved by the institutional review board, and all participants signed the appropriate informed consent forms before the first testing session.
The sedentary group and the pre-season cross-country athletes performed two incremental exercise tests in random order on a Monark 834 cycle ergometer while (a) wearing a commercially available END, and (b) wearing no nasal device (no END). After a 10-minute warm-up and a 5-minute rest period, the test commenced at an initial power level of 66W and was increased by 16W every 2 minutes until voluntary fatigue or until the participants had clearly exceeded acceptable values for LT ([La]blood > 6 mmol·L−1) or RPE level higher than 16. Blood samples were obtained at rest, during the final 30 seconds of each stage, and 1 and 3 minutes into the recovery period.
The in-season crew athletes performed incremental exercise tests during two randomized trial conditions: (a) wearing an END and (b) wearing no END on a Concept II rowing ergometer following the protocol adapted from Womack et al. (32). After a 10-minute warm-up on the exercise ergometer and a 5-minute rest period, the test commenced at an initial rowing pace, which simulated a pace that resulted in a 500-meter row time 20 seconds slower than the subject's goal pace. The subjects were instructed to increase the pace, as visually displayed on the ergometer, so that a 500-meter pace was decreased by 5 seconds for each subsequent stage for five stages. Blood samples were obtained at rest, after each stage, and 1 and 3 minutes into the recovery period.
Each test was performed on separate days, 3 days apart, and the order of the conditions was counterbalanced. We selected the cycle ergometer to minimize local muscle fatigue that could negatively affect performance at high intensities in the sedentary group and pre-season athletes. In contrast, we determined that a sport-specific test that closely resembled their regular exercise routine was more appropriate for the in-season athletes. In addition, the selection of rowers and a rowing protocol allowed for a direct comparison with the findings of a study by Kirkness et al. (14). Each participant served as her own control, so all comparisons were between conditions (END and no END) but not among groups.
Previous studies have used placebos (i.e., without the plastic strips) (12,14), masked the strips under adhesive tape (2), or did not use any device at all (11,20,28) when examining the effectiveness of the END. To maximize any potential effect the END had on increasing ventilation and facilitating aerobic energy production, the subjects in this study were tested either with or without the END. Metabolic gas analysis was not performed in this study because the more practical comparison we were seeking (LT) did not require this measurement and because we lacked the specific mask that would allow for oronasal breathing during the oxygen consumption test. The typical oral ventilation test would clearly be inadequate for this study.
Venous blood (50 μL) was sampled from the earlobe using a capillary tube. Blood lactate concentrations were measured spectrophotometrically (λ = 340 nm) in triplicate using an enzymatic technique (Sigma Diagnostics, procedure 826) for identification of LT. Jones and Doust (13) have demonstrated that the LT has been shown to be highly related to the MLSS, and it is perhaps one of the best indicators of performance in endurance events. The values from the three measurements were averaged, and lactate concentrations were calculated from calibration curves established using lactate standards at known concentrations (r = 0.999, data not shown). Individual data points for blood lactate were plotted to identify LT using the procedures described in Gaskill et al. (10), where the LT was determined by marking the first significant upward deflection of the lactate curve (Figure 1A). It was determined a priori that if there was any disagreement among the investigators as to the determination of LT, the results of that test would be rejected. No data were rejected for this study as there were no disagreements in any of the estimations. We did not conduct experiments to determine the relationship of the LT to the MLSS. However, given the importance of the LT in determining MLSS, we also performed post facto determinations of LT using the three-phase linear model (24) (Figure 1B) and Dmax method (6) (Figure 1C) to verify our estimations of LT. A single-factor analysis of variance (P = 0.05) was used to compare the LT values among methods.
It was hypothesized that if the END was effective in altering the energy production mechanisms, then it would cause increased reliance on aerobic metabolism for any given intensity and consequently lower blood lactate values throughout the submaximal range of the exercise bout. To examine the effects of the END during the exercise period, within-group one-tailed t-tests and Pearson's product moment correlations were used to compare the lactate curves between the two experimental conditions (END vs. no END) for each participant. Significance was set at α = 0.05 for all tests. Between-group comparisons were not performed, as the differences in fitness level and exercise protocol prevented valid or meaningful conclusions from being drawn.
Correlations of blood lactate values for each of the participants from the three subject groups (sedentary, pre-season runners, and in-season rowers) indicated that the lactate values were remarkably similar between the END and no-END experimental conditions (sedentary: range, r = 0.96-0.99; pre-season runners: most in the range r = 0.96-0.99 and one participant r = 0.84; in-season rowers: range, r = 0.96-0.99).
For each of the participants in each of the three groups, the t-test comparisons of all the blood lactate values between the END and no-END trials yielded statistically significant differences in 11 cases (3 in-season, 4 pre-season, and 4 sedentary). However, contrary to expectations, only 2 of those 11 participants had higher lactate values without the END, whereas the remaining 9 participants had higher values while wearing the END. There was no effect of treatment order in these measurements, and the investigators could not discern any identifiable reason for this increase in blood lactate levels with the use of the END.
For all the subjects in the sedentary and the pre-season groups, LT occurred during the second stage of their trials (82W), whereas for all the in-season athletes, LT occurred during the third stage (10 seconds slower than their 500-m time). The sedentary group exhibited the lowest levels of lactate throughout the entire test.
The analysis of variance comparing the LT among different LT determination methods revealed no differences in LT or intensity at LT for any of the lactate threshold determination methods (P = 0.722). In addition, the data from the t-tests indicate that there were no differences between the END and no-END conditions for any of the three groups at LT or any other lactate level or power output (Figure 2). The pre-season group exhibited higher lactate levels for each stage than the sedentary group, and the in-season group exhibited the highest level of lactate at LT, but once again, there were no differences in lactate values at LT (Figure 2).
In all cases, the power of the comparisons was negligible (6.2% for the sedentary group, 8.1% for the pre-season group, and 29.2% for the in-season group). If the experiment was to require a power at a low 50%, the sample size necessary to show effects of the END for the sedentary group would have been 2,195 participants. Accordingly, the sample size would have been 362 participants for the pre-season group and 251 participants for the in-season group. Such studies on the effects of END on LT are not feasible.
This study examined the effects of the END on the LT in three groups of women identified by their training status. We observed no differences in LT with or without the END. Despite assertions about the use of the END during exercise and the rather easy observation that athletes are still using the END extensively, our study is in agreement with existing literature in that it does not support the claims for a performance-enhancing effect of the END (for example, see reference 2). Decreased blood lactate concentration for any given exercise intensity with the use of an END would signify either a reduction in the relative contribution of anaerobic metabolism or the enhanced uptake of lactate from the blood. Given that the time interval between tests was small and the possibility for physiological adaptations in lactate uptake is minimal, our finding means that the END has no effect on the LT during exercise of submaximal intensity.
To consider the effectiveness of this small device in improving performance during exercise, one must examine how the mechanism of action of the END affects the energy production machinery of the body. Reduced nasal airway resistance has been shown to result in lower work of breathing; thus, during nasal breathing, the metabolic work of the respiratory muscles should be lower for any given intensity. An increase in minute ventilation (E) may result in increased o2 by improving the arterial oxygen content and/or mitochondrial respiration. It is precisely this parameter (E) that the manufacturers of the END propose to manipulate for the betterment of aerobic performance. Based on the study by Griffin et al. (12), the manufacturers suggest that with the use of the END, the work of breathing will be more economical, so the person would have lower blood lactate levels for the same mechanical workload. However, given that studies have established that the work of breathing can be lower but without actual change in o2, the potential metabolic benefit of ENDs is negligible. More specifically, it has been shown that inspiratory muscle training resulted in improved cycle performance (4) and lower blood lactate concentration, thus indicating that the work of breathing is lower (16). Based on these findings, O'Kroy (18) argued that if the END is indeed effective in enhancing nasal ventilation and improving alveolar ventilation by reducing the work of the respiratory muscles, then perhaps it is possible that ENDs may have a positive effect on muscle metabolism by increasing oxygen availability and reducing production of lactic acid. However, his results have not demonstrated that the END is effective in altering the ventilatory and cardiovascular profile of progressively increasing exercise (18). Furthermore, Wetter et al. (31) concluded that if there is a significant increase in the work of breathing, this would occur at maximal or near-maximal intensity of exercise (>85% o2max), where ventilation is primarily oral or oronasal; thus, the END would be less, if at all, effective. These studies suggest that even if the END resulted in reduced work of breathing and lower blood lactate levels for any given submaximal intensity of exercise, this effect would be negligible. Finally, it is also possible that, in the present study, performance was not enhanced because the participants shifted to oral or oronasal ventilation and became less dependent on nasal ventilation as exercise becomes more intense (see also reference 17).
It must be noted that no report to date has addressed the potential reasons why the well-conceived study by Griffin et al. (12) stands as the sole peer-reviewed work that presents evidence in support of the effectiveness of ENDs. The study concluded that during very low intensity submaximal exercise on a cycle ergometer, o2, E, heart rate, and RPE were all significantly reduced with use of an END, possibly indicating improved exercise economy, which might translate to increased exercise endurance. However, the study does not provide details as to the fitness level of the participants or whether a particular subset was responsible for the statistically significant differences between the END and the placebo trials. This may be important, given the significantly larger increase in nasal cross-sectional area seen in whites compared with blacks. Finally, it must be noted that the study provides no explanation as to why a subset (23%) of the participant pool did not respond to the application of the END. It is conceivable that those who responded to the END had elevated nasal airway resistance and that the application of the END attenuated this predisposition (9, 15).
In conclusion, the END produced no differences in LT or any other lactate level during submaximal exercise in sedentary women and trained and preseason female athletes.
ENDs are widely used, despite the considerable lack of evidence as to their effectiveness. In the present study, we did not detect any differences in the lactate levels at LT between the END and no-END conditions in the three groups of women we tested (Figure 2). Our data indicate that the END does not lower blood lactate levels during exercise of moderate to high intensity. Our findings are complementary to those in previous studies and fit the conclusions in the brief review by Cerny and Schneider (5). Furthermore, we raise questions as to the findings of the sole study that contradicts our results. This information is important for all who work with athletes, such as coaches, athletic trainers, and support science personnel, because the use of such devices is unwarranted and offers no benefit to the athletes in terms of lower blood lactate levels during exercise of moderate to high intensity.
This work was made possible through the support of a Carson Student Research Grant from Willamette University, Salem, Oregon awarded to G.W. Boggs. The authors wish to thank Mr. Gerrit Southard for his valuable assistance.
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