Influence of inspiratory muscle warm-up on aerobic performance during incremental exercise

Abstract

BACKGROUND:

Endurance is an important factor in athletic performance and is affected by respiratory muscle fatigue. Recent studies indicate that warming up of respiratory muscles improves the respiratory muscle fatigue.

OBJECTIVE:

To investigate the effects of inspiratory muscle warm-up on aerobic performance during incremental exercise.

METHOD:

Maximal inspiratory (MIP) and expiratory (MEP) pressures were measured in 30 healthy male athletes, with (EX) and without (CON) inspiratory muscle warm-up.

RESULTS:

No significant changes in MIP and MEP values between baseline levels and the CON condition were observed while such were seen with respect to EX and between the EX and CON conditions ( $p<$ 0.05). Aerobic performance measurements, including peak oxygen uptake (VO ${}_{\text{2PEAK}}$ ), relative VO ${}_{\text{2PEAK}}$ , oxygen uptake to workrate slope ( $\Delta$ VO ${}_{2}$ / $\Delta$ WR), metabolic equivalent (MET), peak heart rate (HR ${}_{\text{PEAK}}$ ), peak minute ventilation (VE ${}_{\text{PEAK}}$ ), peak tidal volume (TV ${}_{\text{PEAK}}$ ), peak respiratory rate (RR ${}_{\text{PEAK}}$ ), peak carbondioxide output (VCO ${}_{\text{2PEAK}}$ ) and respiratory exchange rate (RER) significantly differed by 18.84%, 19.51%, 9.53%, 15.54%, $-$ 4.36%, 19.90%, 32.77%, $-$ 6.10%, 23.29% and 7.34%, respectively, between subjects in the EX and CON conditions.

CONCLUSION:

These results show that inspiratory muscle warm-up improves aerobic performance byt further investigation is required to elucidate the exact mechanisms that stand behing these variations.

Keywords

Aerobic performance respiratory muscle warming up strength performance

1. Introduction

Warm-up is defined as exercise designed to improve performance efficiency, protect athletes from injury and prepare them for the physiological and psychological loads that accompany improvements in athletic performance; it also reduces muscle damage risk via biomechanic, neurologic and psychologic mechanisms [1]. As warm-up studies become more specialised, the number of inspiratory muscle warm-up, respiratory warm-up and respiratory muscle training studies has increased, and the positive effects of warm-up on athletic performance have been observed [2, 3, 4, 5].

The oxygen demand of tissues increases during sportive activity [6]. The functions of the respiratory system mechanically depend on the capacity of the respiratory muscles [7]. Respiratory muscles are important during exercise, particularly because they lift the rib cage and help in inspiration, and constrict to the rib cage for expiration. Respiratory airflow can reach peak levels via the respiratory muscle strength and effect [8]. A recent study claimed that respiratory muscle warm-up may affects the cooperation of the upper thorax, neck and respiratory muscles and improves levels of reactive O ${}_{2}$ species in muscle tissue by improving muscle O ${}_{2}$ delivery-to-utilisation [9]. These findings highlight the importance of inspiratory muscle warm-up.

The importance of the respiratory system during physical activity has been well-researched, and several scholars have shown that respiratory muscle warm-up could affect athletic performance [2, 3, 4, 10, 11, 12, 13]. Inspiratory warm-up can affect pulmonary functions [9], anaerobic power [13], respiratory muscle strength [11], rowing performance [12], 100 m swimming performance [14], 6 min all-out performance [2], repeated running performance [3], perception of breathlessness and dyspnoea during exercise [4, 7], foot-work performance among badminton players [4], and 6 min performance during treadmill running [7]. However, limited information regarding the effects of inspiratory muscle warm-up on aerobic capacity, an extremely important component of sportive performance, is available.

In the present study, we investigated the impact of inspiratory muscle warm-up on aerobic performance during incremental exercise.

2. Method

2.1 Subjects

A total of 30 healthy male elite field hockey players voluntarily participated in the study (Table 1). The inclusion criteria were at least 10 years of regular hockey training history and at least 5 years of playing in the Turkish Hockey Super League. Athletes with a history of respiratory disease were excluded from the study. The subjects were informed of the study procedure 1 week before commencement. Ethical approval was obtained from the ethical committee of the Ondokuz Mayıs University Head of Medical Research (OMÜ KAEK 2014/635), and informed consent was obtained from all participants included in the study.

Table 1
Descriptive information of subjects ( $N=$ 30)

	Mean $\pm$ SD
Age (years)	20.50	$\pm$ 1.98
Heigth (cm)	179.33	$\pm$ 6.91
Weight (kg)	73.73	$\pm$ 12.72
BMI (kg/m ${}^{2}$ )	22.80	$\pm$ 2.66
MIP (cmH ${}_{2}$ O)	109.90	$\pm$ 10.17
MEP (cmH ${}_{2}$ O)	146.17	$\pm$ 27.13
VO ${}_{\text{2PEAK}}$ (L/min)	3.45	$\pm$ 0.74
Relative VO ${}_{\text{2PEAK}}$ (ml/kg/min)	47.11	$\pm$ 8.00

SD-standard deviation, BMI-body mass index, MIP-maximal inspiratory pressure, MEP-maximal expiratory pressure, VO ${}_{\text{2PEAK}}$ -peak oxygen uptake. Note that VO ${}_{\text{2PEAK}}$ was attained on a maximum-effort incremental test with treadmill.

2.2 Procedure

2.2.1 Design

This study was designed as a randomised, controlled, crossover study and the subjects visited the laboratory four times over the course of our research. During their first visit, they were familiarised with the concepts of maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP) and aerobic performance; they were also informed of the incremental exercise tests and inspiratory muscle warm-up procedure. During their second visit, the MIP and MEP tests were performed without inspiratory muscle warm-up to obtain baseline levels. In the third and fourth visits, the subjects randomly performed experimental trials (EX) with inspiratory warm-up before the MIP and MEP measurements and aerobic performance tests, and performed control trials (CON) without inspiratory warm-up before MIP and MEP measurements and aerobic performance tests. The MIP/MEP measurements and aerobic performance tests were performed immediately after the EX and CON trials. Randomisation and blinding of the CON and EX trials was conducted with trial cards (unseen content) on the third visit. Then, 11 of the subjects performed the EX trial first, and 19 of the subjects performed the CON trial first. The subjects had no knowledge of which tests would apply after the CON and EX trials. Blinding was used to eliminate potential biases during the incremental exercise test. The trials were performed at intervals of 1 day and at the same time each day (between 16:00 and 20:00). Exercise and high-intensity physical activity were not allowed before the trials.

2.2.2 Inspiratory warm-up procedure

A specific inspiratory training device (Power ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}{\textregistered}}$ Breathe Classic, IMT Technologies Ltd., Birmingham, UK) was used for the inspiratory warm-up procedure. For the EX trial, two sets of 30 inspirations were performed at an intensity of 40% of the MIP with a 2 min rest between each set [3, 9, 13, 15, 16].

Table 2
The analysis in the MIP and MEP measurements between baseline level and trials

	Baseline		CON	EX
MIP (cmH ${}_{2}$ O)	109.90 $\pm$ 10.17		110.87 $\pm$ 11.76	119.60 $\pm$ 13.77 ${}^{\text{a},\text{b}}$
		Difference from baseline (cmH ${}_{2}$ O)	0.97	9.7
		Percent change from baseline (%)	0.88	8.83
MEP (cmH ${}_{2}$ O)	146.17 $\pm$ 27.13		147.63 $\pm$ 29.83	153.07 $\pm$ 25.77 ${}^{\text{a},\text{b}}$
		Difference from baseline (cmH ${}_{2}$ O)	1.46	6.9
		Percent change from baseline (%)	1.00	4.72

MIP-maximal inspiratory pressure, MEP-maximal expiratory pressure, CON-control trial, EX-experimental trial. ${}^{\text{a}}$ Significant difference between the EX trial and baseline level. ${}^{\text{b}}$ Significant difference between the EX and CON trials.

2.2.3 MIP and MEP measurement

MIP and MEP were measured with a respiratory pressure meter (MicroRPM, CareFusion Micro Medical, Kent, UK) according to the 2002 guidelines of the American Thoracic Society and European Respiratory Society (2002) [6]. MIP measurements were obtained from the residual volume, and MEP measurements were obtained from the total lung capacity. The nose was occluded throughout these efforts. To obtain the best value, all subjects were measured from three to five times until the difference between two attempts differed by no more than 10%. The maximal of three acceptable attempts was used as the final MIP or MEP value [9, 17, 18, 19].

2.2.4 Aerobic performance test (VO ${}_{\text{2PEAK}}$ )

VO ${}_{\text{2PEAK}}$ measurements were conducted with a cycle ergometer (SanaBike 450F, Ergosana GMBH, Bitz, Germany) and an ergospirometer (Ergo 100 PFT System, Medical Electronic Construction R&D, Brussels, Belgium). Each subject warmed up at least for 15 min before the exercise. The exercise load was begun at 50 W and increased by 25 W/min. The subjects were cycled at 60 rpm over the entire course of exercise. Oxygen uptake was measured breath-by-breath, and the system was calibrated with standardised gases before each test. The subjects were verbally motivated and encouraged to give their full effort. When the subjects felt exhaustion or failed to maintain a pedal cadence of $>$ 50 rpm, the exercise ended and VO ${}_{\text{2PEAK}}$ values were recorded [20].

2.3 Data analysis

SPSS version 16.0 (SPSS Inc., Chicago, IL, USA) was used for all statistical analyses. The data were expressed as either mean $\pm$ standard deviation or percentage of mean difference. The ShapiroWilk test was used to assess normality. Repeated-measures one-way analysis of variance and Bonferroni correction were used to analyse differences in MIP and MEP measurements between the baseline, CON and EX trials. Paired-sample $t$ test was used to analyse aerobic performance values among subjects in the CON and EX trials. Significance was defined as $p\leqslant$ 0.05.

3. Results

3.1 Effects on the MIP and MEP measurements

Table 2 indicates that significant improvements in the MIP and MEP values resulted due to the EX, but not with respect to the CON condition. There were also significant between- conditions differences.

Table 3
The analysis in the aerobic performance measurements between the CON and EX trials

	CON		EX
VO ${}_{\text{2PEAK}}$ (L/min)	3.45 $\pm$ 0.74		4.10 $\pm$ 0.87 ${}^{*}$
		Difference from CON (L/min)	0.65
		Percent change from CON (%)	18.84
Relative VO ${}_{\text{2PEAK}}$ (ml/kg/min)	47.11 $\pm$ 8.00		56.30 $\pm$ 10.86 ${}^{*}$
		Difference from CON (ml/kg/min)	9.19
		Percent change from CON (%)	19.51
$\Delta$ VO ${}_{2}$ / $\Delta$ WR (mlO ${}_{2}$ .min ${}^{-1}$ .W ${}^{-1})$	13.43 $\pm$ 2.20		14.71 $\pm$ 3.29 ${}^{*}$
		Difference from CON (mlO ${}_{2}$ .min ${}^{-1}$ .W ${}^{-1})$	1.28
		Percent change from CON (%)	9.53
Metabolic Equivalent (MET)	14.48 $\pm$ 2.76		16.73 $\pm$ 3.39 ${}^{*}$
		Difference from CON (MET)	2.25
		Percent change from CON (%)	15.54
HR ${}_{\text{PEAK}}$ (beat/min)	172.63 $\pm$ 15.61		165.10 $\pm$ 18.61 ${}^{*}$
		Difference from CON (beat/min)	$-$ 7.53
		Percent change from CON (%)	$-$ 4.36
VE ${}_{\text{PEAK}}$ (L/min)	84.01 $\pm$ 25.52		100.73 $\pm$ 25.21 ${}^{*}$
		Difference from CON (L/min)	16.72
		Percent change from CON (%)	19.90
TV ${}_{\text{PEAK}}$ (L/breath)	2.38 $\pm$ 0.74		3.16 $\pm$ 1.73 ${}^{*}$
		Difference from CON (L/breath)	0.78
		Percent change from CON (%)	32.77
RR ${}_{\text{PEAK}}$ (breath/min)	41.00 $\pm$ 6.84		38.50 $\pm$ 5.91 ${}^{*}$
		Difference from CON (breath/min)	$-$ 2.50
		Percent change from CON (%)	$-$ 6.10
VCO ${}_{\text{2PEAK}}$ (L/min)	3.65 $\pm$ 0.86		4.50 $\pm$ 0.93 ${}^{*}$
		Difference from CON (L/min)	0.85
		Percent change from CON (%)	23.29
RER (VCO ${}_{2}$ /VO ${}_{2}$ )	1.09 $\pm$ 0.10		1.17 $\pm$ 0.10 ${}^{*}$
		Difference from CON (VCO ${}_{2}$ /VO ${}_{2}$ )	0.08
		Percent change from CON (%)	7.34

CON-control trial, EX-experimental trial, VO ${}_{\text{2PEAK}}$ -peak oxygen uptake, $\Delta$ VO2/ $\Delta$ WR-oxygen uptake to workrate slope, HR ${}_{\text{PEAK}}$ -peak heart rate, VE ${}_{\text{PEAK}}$ -peak minute ventilation, TV ${}_{\text{PEAK}}$ -peak tidal volume, RR ${}_{\text{PEAK}}$ -peak respiratory rate, VCO ${}_{\text{2PEAK}}$ -peak carbondioxide output, RER-respiratory exchange ratio. ${}^{*}$ -significant difference between the EX and CON trials.

Figure 1.

Percent difference in the MIP and MEP between the baseline level, CON and EX trials. CON-control trial, EX-experimental trial, MIP-maximal inspiratory pressure (straight line), MEP-maximal expiratory pressure (dotted line).

3.2 Effects on the aerobic performance

Table 3 outlines the results of the aerobic performance parameters obtained between the EX and CON conditions. Significant changes in all aerobic performance parameters were observed including VO ${}_{\text{2PEAK}}$ (CON: 3.45 $\pm$ 0.74 L/min, EX: 4.10 $\pm$ 0.87 L/min), relative VO ${}_{\text{2PEAK}}$ (CON: 47.11 $\pm$ 8.00 mL/kg/min, EX: 56.30 $\pm$ 10.86 mL/kg/min), $\Delta$ VO ${}_{2}$ / $\Delta$ WR (CON: 13.43 $\pm$ 2.20 mLO ${}_{2}$ /min/W, EX: 14.71 $\pm$ 3.29 mLO ${}_{2}$ / min/W), metabolic equivalent (CON: 14.48 $\pm$ 2.76 MET, EX: 16.73 $\pm$ 3.39 MET), HR ${}_{\text{PEAK}}$ (CON: 172.63 $\pm$ 15.61 beat/min, EX: 165.10 $\pm$ 18.61 beat/min), VE ${}_{\text{PEAK}}$ (CON: 84.01 $\pm$ 25.52 L/min, EX: 100.73 $\pm$ 25.21 L/min), TV ${}_{\text{PEAK}}$ (CON: 2.38 $\pm$ 0.74 L/breath, EX: 3.16 $\pm$ 1.73 L/breath), RR ${}_{\text{PEAK}}$ (CON: 41.00 $\pm$ 6.84 breath/min, EX: 38.50 $\pm$ 5.91 breath/min), VCO ${}_{\text{2PEAK}}$ (CON: 3.65 $\pm$ 0.86 L/min, EX: 4.50 $\pm$ 0.93 L/min) and RER (CON: 1.09 $\pm$ 0.10 VCO ${}_{2}$ /VO ${}_{2}$ , EX: 1.17 $\pm$ 0.10 VCO ${}_{2}$ /VO ${}_{2})$ . Percentagewise these EX-CON differences amounted to 18.84%, 19.51%, 9.53%, 15.54%, $-$ 4.36%, 19.90%, 32.77%, $-$ 6.10%, 23.29% and 7.34% for VO ${}_{\text{2PEAK}}$ , relative VO ${}_{\text{2PEAK}}$ , $\Delta$ VO ${}_{2}$ / $\Delta$ WR, metabolic equivalent, HR ${}_{\text{PEAK}}$ , VE ${}_{\text{PEAK}}$ , TV ${}_{\text{PEAK}}$ , RR ${}_{\text{PEAK}}$ , VCO ${}_{\text{2PEAK}}$ and RER, respectively (Figs 2 and 3).

Figure 2.

Percent difference in the aerobic performance parameters between the CON and EX trials. CON-control trial, EX-experimental trial, VO ${}_{\text{2PEAK}}$ -maximum oxygen uptake, $\Delta$ VO2/ $\Delta$ WR-oxygen uptake to workrate slope, MET-metabolic equivalent.

Figure 3.

Percent difference in the respiratory and circulatory parameters that support the change in aerobic performance parameters between the CON and EX trials. CON-control trial, EX-experimental trial, HR ${}_{\text{PEAK}}$ -peak heart rate, VE ${}_{\text{PEAK}}$ -peak minute ventilation, TV ${}_{\text{PEAK}}$ -peak tidal volume, RR ${}_{\text{PEAK}}$ -peak respiratory rate, VCO ${}_{\text{2PEAK}}$ -peak carbondioxide output, RER-respiratory exchange ratio.

4. Discussion

The aim of the present study was to investigate the effects of inspiratory warm-up on aerobic performance. Two major findings were obtained: [1] After inspiratory warm up, the relative and absolute VO ${}_{\text{2PEAK}}$ showed large increments from the CON trial ( $p<$ 0.05) and [2] MIP and MEP measurements showed a significant increase compared with the corresponding baseline levels ( $p<$ 0.05). All other aerobic performance measurements showed significant improvements after inspiratory warm-up ( $p<$ 0.05). However, the MIP and MEP measurements did not show any significant differences between the CON trial and baseline values ( $p>$ 0.05).

The effect of warm-up on aerobic capacity could be attributed to increases in initial VO ${}_{2}$ levels before exercise. Thus, much less a portion of initial work load is handled by anaerobic energy system [21]. The amount of O ${}_{2}$ reaching the muscles, dissociation of oxyhaemoglobin and expansion of the muscle vessels increase because of warming up [22]. After warming up, increases in muscle temperature cause improved O ${}_{2}$ consumption of the muscle mitochondria and decrease the ratio between adenosine triphosphate regeneration and mitochondrial VO ${}_{2}$ [23]. As a result of these activities, reactions related to oxidative phosphorylation speed up, and the capacity of the muscles for aerobic energy production increases [24]. These physiological effects depend on the time and intensity of warm-up. Inadequate warm-up impedes the occurrence of these effects, while excessive warm-up time and intensity cause fatigue and reductions in aerobic performance [24]. A number of studies have demonstrated the null effect [25, 26] or the negative effects [26, 27, 28] of warm-up on aerobic performance. A similarity may be observed between the effects of general warm-up and respiratory warm-up on aerobic performance, and respiratory muscles play an important role in aerobic performance considering that aerobic capacity depends on O ${}_{2}$ consumption.

Recent studies on the effects of respiratory muscle warm-up have shown significant increments in long-term performance [2, 3, 4, 7, 16, 29]. In contrast to these studies, however, some studies have indicated decrements in long-term exercise performance [5, 18]. Such decrements have been attributed to the performance of paraplegic subjects [5] and the high intensity of long-term exercise [18].

Respiratory muscle warm-up does not raise the O ${}_{2}$ percentage in the blood that completes pulmonary circulation [30]. Nevertheless, respiratory muscle warm-up causes increments in the functional capacity of respiratory muscles [11, 9] and decrements in respiratory muscle fatigue [2, 19]. These effects may be explained by increases in the temperature of muscle tissue, contraction ability of muscles, contraction strength of muscles and more efficient use of generated power of muscles [10]. Recent studies have shown improvements in respiratory muscle strength after inspiratory muscle warm-up [2, 3, 4, 5, 7, 12, 15, 29], similar to the findings of the present study. Therefore, the positive effects of inspiratory muscle warm-up on aerobic performance observed in the current study could be related to improvements in respiratory muscle strength.

The observed increase in aerobic performance in the present study can be explained by improvements in thoracic geometry [31], the contributions of the upper thorax and neck muscles to the respiratory muscles [31, 32, 33] and improvements in neural pathways [34] accompanying increases in respiratory muscle strength. A previous study claimed that prior contractions, similar to inspiratory muscle warm-up, probably might explain the presence of increased levels of reactive O ${}_{2}$ species in muscle tissue and improvements in muscle O ${}_{2}$ delivery-to-utilisation [9]. The effect of inspiratory warm-up on athletic performance may potentially be explained by these mechanisms.

As for a possible limitation of this study, it should be mentioned that it was designed as a randomised, controlled, crossover study. Placebo-controlled design could be an alternative and may be used in another endeavour.

In conclusion, inspiratory muscle warm-up significantly improve aerobic performance compared with baseline levels. The mechanisms responsible for these improvements are probably associated with improvements in inspiratory-expiratory muscle strength, increases in levels of reactive O ${}_{2}$ species in the muscle tissue, improvements in muscle O ${}_{2}$ delivery-to-utilisation and cooperation of the upper thorax, neck and respiratory muscles. Further investigation is required to determine the precise mechanisms from among these candidates. The findings showed that inspiratory warm-up positively affects aerobic performance. When considering the significance of aerobic performance in athletic performance and daily life, inspiratory warm-up may be used as an ergogenic aid or intensive therapy.

Footnotes

Conflict of interest

This project was not supported by any grants or other financial assistance and the authors declare no conflict of interest. The present study is a part of doctoral dissertation of Dr. Mustafa Özdal.

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Influence of inspiratory muscle warm-up on aerobic performance during incremental exercise

Abstract

BACKGROUND:

OBJECTIVE:

METHOD:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Method

2.1 Subjects

Table 1 Descriptive information of subjects ( N = 30)

2.2.1 Design

2.2.2 Inspiratory warm-up procedure

Table 2 The analysis in the MIP and MEP measurements between baseline level and trials

2.2.4 Aerobic performance test (VO 2PEAK )

2.3 Data analysis

3. Results

3.1 Effects on the MIP and MEP measurements

Table 3 The analysis in the aerobic performance measurements between the CON and EX trials

Footnotes

Conflict of interest

References

Table 1
Descriptive information of subjects ( $N=$ 30)

Table 2
The analysis in the MIP and MEP measurements between baseline level and trials

2.2.4 Aerobic performance test (VO ${}_{\text{2PEAK}}$ )

Table 3
The analysis in the aerobic performance measurements between the CON and EX trials