Resistance training is an effective exercise modality for increasing muscle strength and mass, which are important components of fitness and health (Bird et al., 2005; Winett and Carpinelli, 2001). To optimize training response requires manipulation of acute training variables (e.g., frequency, intensity, and volume) with careful consideration given to training experience to ensure the program is individualized (Kraemer and Ratamess, 2004). Resistance training volume (sets×repetitions) is considered to be an important determinant of muscle strength and hypertrophy. Even though increases in muscle strength can be achieved when performing lower-volume resistance training (<3 sets per exercise), it appears that higher volume resistance training (≥3 sets per exercise) results in larger gains (Krieger, 2009, 2010). Consequently, to maximize muscle hypertrophy it is recommended that higher volume (3–6 sets of 6–12 repetitions) and moderate load (70%–85% one-repetition maximum [1RM]) resistance training sessions are prioritized (Ratamess et al., 2009). These training practices are associated with increased metabolic acidosis and ventilatory demand compared to lower-volume resistance training sessions (Kang et al., 2005; Wirtz et al., 2014). The increased physiological demands from higher volume resistance training sessions may lead to adaptations that may enable training with heavier loads for longer (i.e., improved muscle endurance) (Radaelli et al., 2015), thus better session tolerance (e.g., less symptoms of dizziness and nausea) (Kraemer and Ratamess, 2004). Additionally, it seems plausible that higher volume resistance training may induce positive changes in lung function. Improved lung function has been shown following resistance training in people with chronic obstructive pulmonary disease (Strasser et al., 2013), however, there is a paucity of research on this topic in apparently healthy populations.

For lung function to be improved following high-volume resistance training it would be expected that lung function parameters would be acutely impaired following a training bout. Such a hypothesis is based on training adaptation theories which suggest that an adequate training stimulus would result in the accumulation of fatigue, which in this case would be a reduction lung function, and upon recovery an improvement in performance (Cunanan et al., 2018). Diminished lung function has been observed following marathon and ultramarathon running (Tiller, 2019) and after a CrossFit (i.e., a form of high-intensity interval training) bout (Shaw et al., 2015). Furthermore, superior lung function performance has been observed in endurance athletes compared to strength and power athletes (Lazovic et al., 2015). This suggests that lung function adaptations from exercise training are dependent on the nature of the exercise (e.g., type, frequency, intensity, and duration). Khosravi et al. (2013) found that changes in lung function parameters following resistance training were minimal compared endurance training. Although, this previous study implemented a resistance training program involving mostly isolated (i.e., single joint) exercises, whereas programs with a greater emphasis on compound (i.e., multi joint) exercises are considered to be more effective for enhancing muscle adaptation and are more commonly used by experienced trainers (Paoli et al., 2017). It should also be noted that compound exercises such as the squats and deadlifts require increased activation of the respiratory muscles such as the diaphragm to assist with spine stability (Martuscello et al., 2013). Therefore, it seems plausible that the increased respiratory muscle work from assisting with spine stability together with elevated ventilation demands from high-volume resistance training would place significant stress on the respiratory system leading to an acute reduction in lung function performance.

To date, no study has investigated whether lung function is acutely affected following physically demanding resistance training sessions. The aim of this study was to examine whether a high-volume compared to a low-volume whole-body resistance exercise session acutely impairs lung function. It was hypothesized there would be evidence of reduced lung function performance following the high-volume compared to low-volume resistance exercise session.

This study used a crossover, repeated measures design with random allocation of participants into three sequences (high-volume, low-volume, and control sessions). Fourteen males (age, 23.8±6.5 years; body mass, 83.2±7.2 kg; stature, 179.2±4.3 cm) with 4.6±2.1 years of resistance training experience participated in this study. Their one-repetition maximum (1RM) was 97.5±17.1 kg for the bench press, 125.5±18.3 kg for squat, 59.3±13.1 kg for shoulder press, and 139.6±25.0 kg for deadlift. The eligibility criteria for this study included being male, aged 18–45 years, ≥1-year resistance training experience, and having the ability to perform the bench press, shoulder press, squat, and deadlift. The exclusion criteria included asthma, current respiratory illness, medications that could influence lung function and any chronic disease or condition. Verbal and written consent was provided by all participants prior to study commencement. This study was approved by the University of Sydney Human Research Ethics Committee (approval number: 2014/977).

Upon enrolment into the study, participants visited the exercise laboratory to become familiarised with lung function testing which involved performing a minimum of three trials for each measure described below. Based on these initial results all participants were deemed to have normal lung function (Johnson and Theurer, 2014). During the same visit, participants performed 1RM tests for the resistance exercises that were to be performed in the exercise sessions. Following the 1RM testing, each participant was given an opaque sealed envelope which contained a randomly assigned sequence for the three experiment sessions.

No significant differences were found between conditions for presession results for any lung function measure. There were no significant differences found for FVC, SVC, FEV₁, FEV₃, FEV₆, ERV, and MVV between pre- and postsession for the control, 2-SETS, and 5-SETS (Table 1). A greater increased in FEV₁/FVC was found following the 5-SETS compared to 2-SETS (P=0.033), with a trend approaching significance when compared to the control session (P=0.071). A significant reduction in IC was observed following 5-SETS compared to control session (P=0.049) but no difference was found compared to 2-SETS (P>0.05).

Mean recovery VO₂, VE, and tidal volume were greater for squats compared to bench press (P<0.001) and shoulder press (P<0.001) (Fig. 1). Similarly, greater mean recovery VO₂, VE, and tidal volume were found for deadlifts compared to bench press (P<0.001) and shoulder press (P<0.001). Mean respiratory rate was higher for squat and deadlift compared to bench press (P=0.013 and P<0.001, respectively). Mean recovery heart rate was higher during deadlifts compared to bench press (P<0.001) and shoulder press (P=0.024). Higher heart rates were also found for squats compared to bench press (P<0.001). The mean recovery PETCO₂ was lower during the shoulder press compared to bench press (P=0.001) and for deadlift compared to bench press (P=0.045). During the 5-SETS there was a lower PETCO₂ for the bench press (P=0.013), squat (P=0.003), shoulder press (P=0.008), and a trend was found with deadlift (P=0.082) (Fig. 1). There were no other significant differences between the 2-SETS and 5-SETS for VO₂, VE respiratory rate, tidal volume, and heart rate.

Session duration was greater for 5-SETS (66.4±12.7 min) compared to 2-SETS (21.4±3.7 min) (P<0.001). Total training volume was significantly greater for 5-SETS (13,235.4±1,939.9 kg) compared to 2-SETS (5,518.2±762.3 kg) (P<0.001). For each individual exercise (bench press, squat, shoulder press, and deadlift) training volume was greater during 5-SETS (P<0.001). The full 10 repetitions could be completed for 98.6% of the assigned sets for 2-SETS compared to 87.5% of sets for 5-SETS. For individual exercises during 5-SETS participants performed <10 repetitions for the shoulder press during 22.9% of sets, followed by bench press (12.9%), squat, and deadlift (both 7.1%).

In resistance-trained males, the present study showed there were minimal alterations in lung function following low-volume and high-volume whole-body resistance exercise sessions. There was a slight improvement in FEV₁/FVC following 5-SETS compared to 2-SETS. In contrast, IC was diminished following 5-SETS compared to the control session suggestive of respiratory muscle fatigue. Although, there were no other differences found between conditions for all other lung function measures which is in disagreement with the original hypothesis. Greater physiological demands were found for both the squat and deadlift compared to the upper body exercises as indicated by accentuation of the VO₂, ventilatory parameters, and heart rate responses for the former exercises. However, there was higher metabolic stress observed during the high-volume session as indicative by the lower PETCO₂ observed following most exercises during the 5-SETS compared to 2-SETS. Additionally, the strenuous nature of the high-volume session was evident from a larger percentage of participants being unable to complete the desired number of repetitions during exercises. Based on the present study findings it appears that lung function remains relatively stable following an acute physically demanding resistance training bout in resistance-trained males.

It was previously unknown whether lung function would be affected by a more metabolically demanding resistance training bout. The finding of greater FEV₁/FVC following the high-volume compared to low-volume session suggests mild bronchodilation that facilitated increased air flow without a significant increase in airway resistance. A possible explanation could be the increased metabolic demand of the higher volume session acutely improving smooth muscle and bronchial compliance (Milanese et al., 2009; Tipton et al., 2017). Although, it was also observed that IC was diminished following the high-volume session compared to the control session which provides evidence that inspiratory muscle function was acutely impaired. The main inspiratory muscle is the diaphragm (Enright et al., 2006), and this muscle together with other respiratory muscles assists with stabilisation of the trunk during exercises with high axial loading such as deadlifts and squats (Aasa et al., 2019). The high-volume session most likely required slightly greater work to be accomplished by the inspiratory muscles from the perspective of ensuring adequate trunk stabilisation, thus leading to inspiratory muscle fatigue. Previously Gomez et al. (2009) found that sit-ups performed to volitional fatigue resulted in diminished respiratory muscle strength while indices of lung function remained unaffected. Therefore, supporting the theory that fatigue of the respiratory muscles can be induced without high ventilatory demands for sustain periods which seems to be the main culprit contributing to respiratory muscle fatigue following aerobic exercise (Romer and Polkey, 2008).

Impairment in lung function has been reported following a CrossFit session (Shaw et al., 2015) as well as following marathon and ultramarathon running (Tiller, 2019). Aerobic exercise is associated with higher VO₂ and VE responses compared to resistance exercise, which is considered to be an anaerobic exercise (Vilaça-Alves et al., 2016). During resistance training, peak VO₂ and VE occur in the recovery between sets of an exercise as opposed to during the actual exercise, and then it plummets back down to pre-exercise VO₂ and VE (Scott, 2011; Scott et al., 2009). The intermittent nature of resistance exercise means that VO₂ and VE are not elevated to levels significantly above pre-exercise values for sustained periods, unlike aerobic exercise. However, during strenuous resistance exercise VE will increase disproportionately in relation to VO₂ due to its relatively large anaerobic component (lactate accumulation) increased carbon dioxide and subsequent H⁺ concentrations (De Sousa et al., 2012; Lühker et al., 2017).

In the present study, a hyperventilatory response was demonstrable through decreases in PETCO₂ following each exercise. Since recovery PETCO₂ was significantly lower for the 5-SET compared to 2-SET there is further evidence of greater respiratory muscle demands during the high-volume resistance training bout (Romer and Polkey, 2008). It was hypothesized that the increased ventilatory demands (i.e., hyperventilation) coupled with the requirements of the abdominals to maintain trunk stability during the high- volume session would increase the work performed by the respiratory muscles, thus leading to alterations in indices of lung function (Aliverti, 2016). However, the respiratory demands during the high-volume session were likely insufficient to impair lung function since there was no difference between the 5-SETS and 2-SETS for any lung function parameter.

Minimal improvements in lung function indices have been shown following resistance training of moderate-high volume (2–4 sets per exercise) and intensity (60%–80% 1RM) within healthy adults (Khosravi et al., 2013). In this previous study, MVV was the only lung function parameter which improved following resistance training. The MVV test is commonly used to assess the strength and endurance of the inspiratory and expiration muscles (Green et al., 2002). Due to the diminishment in respiratory muscles strength found by Gomez et al. (2009) following sit-ups to volitional fatigue, if respiratory muscle strength was adversely affected following the high-volume session it is reasonable to assume that MVV performance would also be affected. However, it has been argued that while respiratory muscle strength is important for sustaining ventilation, performance in the MVV test is influenced by many factors (e.g., respiratory system mechanics and respiratory muscle endurance) (Neufeld et al., 2018), therefore a reduction in respiratory muscle strength may not affect MVV performance. This might also explain why other lung function indices were unaffected following the high-volume session. In other words, unless respiratory muscle strength is severely affected as a result of a chronic condition (Fitting, 2001; Singer et al., 2011) or extremely demanding exercise session (e.g., marathon run) (Tiller, 2019), lung function parameters would remain relatively stable, as was found within the present study. Other factors that influence lung function include the compliance of the lungs, condition of the ventilatory control systems, and resistance of both airways and tissues (Ionescu et al., 2009; Lalley, 2013). Although these factors are unlikely to affect lung function in healthy young adults following exercise performed at lower ventilatory demands than intense or sustained aerobic exercise.

Powerlifters have been shown to possess greater diaphragm mass and respiratory muscle strength compared to untrained healthy adults (Brown et al., 2013). Furthermore, the effectiveness of resistance training on respiratory muscle strength has been confirmed in apparently healthy (DePalo et al., 2004) and clinical populations (Menezes et al., 2016). Therefore, based on training adaptation theories an adequate training stimulus to promote improvement in lung function would present as an acute decrease in lung function (Cunanan et al., 2018). It is possible that the resistance-trained participants could cope with very demanding resistance exercise sessions without experiencing alterations in lung function postexercise due chronic training adaptations to their respiratory systems (Brown et al., 2013; DePalo et al., 2004). Further, potentially a ceiling effect may have resulted in no further improvements in lung function following attaining a certain level of resistance training experience. If an untrained population was used within the present study instead of a resistance-trained group, the effect of the high-volume resistance training session on lung function may have been different. Greater improvements in lung function were found in healthy previously inactive subjects following aerobic training combined with resistance training compared to resistance training alone (Khosravi et al., 2013). Therefore, resistance training might be efficacious for improving respiratory muscle strength, while aerobic training, either alone or in combination with resistance training seems to be most effective for improving lung function in healthy adults.

This study revealed that lung function was largely unaffected within a group of experienced male resistance trainers following a high-volume compared to a low-volume whole-body resistance exercise session. The physical demands of the high-volume session appeared insufficient to lead to any change in lung function compared to the low-volume session. Training adaptations to the respiratory system might have protected resistance trainers from experiencing reductions in lung function following the high-volume session. Another possibility is that resistance exercise is less likely to acutely affect lung function following a strenuous training session compared to intense aerobic exercise.