Breathing behavior during resistance exercise is closely matched to the different phases of a lift. General recommendations include exhaling through the sticking point (the part of the lift with least mechanical advantage) during the concentric phase and inhaling through the eccentric phase (49,52). However, when lifting heavy loads (>80% maximal voluntary contraction [MVC]), a brief Valsalva maneuver (VM), or the forced exhalation against a closed glottis, is unavoidable (34). Similarly, when lifting lighter loads repeatedly until failure, the VM must be invoked as motor units progressively fatigue (34). These observations suggest that the VM is a natural reflex that is evoked during resistance exercise when greater efforts are required.
The proposed benefit of the VM during resistance exercise is increased stability of the spine due to augmented intra-abdominal pressure (IAP) (11,40). Shirley et al. (47) demonstrated that spinal stiffness, thus stability, is increased when IAP is elevated. Stability of the spine is crucial for providing a foundation for movement of the upper and lower extremities, to support loads, and for protection of structures of the lower back (53). Strength and conditioning experts acknowledge that a brief VM (no longer than 3 seconds in duration) could assist the experienced resistance trainer by maintaining proper vertebral alignment and support and reducing lower back injury risk (4). However, the effect of the VM on IAP has not been systematically evaluated. Furthermore, the VM is associated with a pronounced rise in systolic blood pressure and individuals with a history of heart and cardiovascular disease are advised to avoid the VM during resistance exercise (52).
The purpose of this systematic review was to examine the extent and quality of current research literature, to evaluate the efficacy of the VM on increasing IAP and the safety of performing the VM during resistance exercise. It was hypothesized that the VM alone would increase IAP and that performing the VM compared with free breathing (i.e., avoiding the VM) during resistance exercise would augment IAP. It was also hypothesized that performing the VM compared with free breathing during resistance exercise would elevate blood pressure response. To date, no systematic review has been conducted to assess the efficacy of the VM on increasing IAP and the associated risks of performing the VM during resistance exercise. Such information would be useful for strength and conditioning coaches when giving advice to trainers on how to breathe during a resistance exercise.
Experimental Approach to the Problem
Avoiding the VM may be possible for resistance trainers when lifting at lower intensities; however, this is unrealistic when following resistance training guidelines aimed at maximizing muscular strength and hypertrophy (i.e., using ≥80% 1 repetition maximum [1RM] loads or performing repetition maximums) where the VM is unavoidable. Although it is claimed that the VM is evoked during high-intensity lifts to increase spinal stability via increased IAP, the reported exaggerated hemodynamic responses has led to health authorities advising against its usage during resistance exercise. To evaluate if the VM is effective for increasing spine stability (i.e., indirectly via IAP) and the health risks associated with its use during a lift, a systematic review was conducted. Electronic database searches were performed in AMED (via OvidSP), CINAHL (via EBSCO), Cochrane Central Register of Controlled Trials (via OvidSP), Embase, MEDLINE (via OvidSP), PubMed, SPORTDiscus (via EBSCO), and Web of Knowledge from earliest record to March 2011. Relevant studies were combined to provide an overview of research on this topic. Conclusions were based on the literature with suggested practical applications for strength and conditioning coaches.
Two separate searches were conducted to examine the effect of the VM on: (a) IAP and (b) hemodynamics during resistance exercise and reported adverse events. In the 2 searches, key word searches were performed (detailed hereafter) after which duplicates were eliminated and search results were screened against inclusion/exclusion criteria (detailed in Search 1-Effect of VM on IAP and Search 2-Is Performing the VM During Resistance Exercise a Safe Practice?). Those references with indeterminate relevance by title or abstract were retrieved and reviewed. Reference lists of all retrieved articles were also manually searched for potentially eligible papers.
Search 1—Effect of the VM on IAP
Titles and abstracts were searched using the key words “Valsalva” and “intra-abdominal pressure” or “intra abdominal pressure” or “abdominal pressure” or “IAP.” To be included, articles must have (a) used apparently healthy subjects, (b) reported maximum IAP from the VM (either alone or during a resistance exercise), and (c) measured IAP directly via intragastric or intrarectal pressure transducer or ingested telemetry tablet or indirectly via bladder pressure. Articles were excluded if subjects had a history of lower back pain.
Search 2—Is Performing the VM During Resistance Exercise a Safe Practice?
Titles and abstracts were searched using the key words “Valsalva” and “weight*” or “resistance training” or “resistance exercise” or “strength training” and “blood pressure” or “cardiovascular*” or “heart*” or “stroke*” or “cerebral*” or “cerebrovascular*” or “retina*” or “aneurysm” or “blindness” or “hematoma” or “haematoma” or “headache” or “hernia” or “hemorrhage” or “haemorrhage” or “maculopathy” or “pneumothorax” or “pneumomediastinum.” To be included, articles must have (a) used apparently healthy subjects, (b) actively instructed or reportedly used the VM during a resistance exercise, and (c) used subjects who reported not using anabolic steroids or performance enhancing drugs. Articles were excluded if the adverse event was reported during activities other than resistance exercise, such as laboring tasks, trumpet playing, and pregnancy.
Using a systematic approach, as opposed to a narrative literature review, helped minimize biases (systematic errors) and random errors (simple mistakes). Despite not rating studies included in the review for internal validity and statistical reporting (e.g., PEDro scale), the methodological quality was considered high because only articles with acceptable assessment and measure of IAP (e.g., using intragastric pressure transducers and VM alone performed after full inspiration) and hemodynamics (e.g., measuring blood pressure via capacitance transducer connected to a catheter in the brachial artery) were included in the review. Due to study heterogeneity, it was deemed that the data were not suitable for pooling, and a meta-analysis was not performed. Studies investigating the effect of the VM (independent variable) on IAP or hemodynamics (e.g., blood pressure, heart rate, stroke volume, and cardiac output) (dependent variables) accepted statistical significance at p < 0.05. Data are reported as mean ± SD. For studies that did not directly examine the effect of the VM on IAP or hemodynamics, data are reported as mean ± SD or as a range without p values. The data reported are for a given day unless otherwise stated with test-retest reliability of data reported in parentheses.
Effect of the VM on IAP
The database searches identified 434 articles. Review of titles and abstracts revealed that 406 articles did not meet the inclusion/exclusion criteria. The full texts of the remaining 28 articles were reviewed for more detailed evaluation and resulted in the exclusion of 14 articles. Based on the eligibility criteria, 14 articles were included in the final analysis (Table 1).
Thirteen studies reported IAP from the VM alone, with 6 of these studies also reporting IAP during resistance exercise without being instructed to perform a VM (14,22,28,38,39,51). Two studies reported IAP from a VM during resistance exercise (12,40). Of the 14 available studies, 6 were in male-only cohorts(11–13,22,28,39), 6 studies combined males and females (7,9,14,15,40,51), and 2 studies did not report sex (18,38). Two studies examining IAP from the VM were undertaken in trained individuals (weightlifters and judo fighters) (14,28), whereas most studies were performed in individuals who did not participate in regular resistance training or activities involving exposure to heavy trunk loads, that is, body contact sports. Measurement of IAP was most commonly performed intragastrically (9 studies) (7,11–15,22,38,51) with 2 studies measuring intrarectally (28,39), 2 by telemetry tablet (18,40), and 1 intravesically (9). IAP from the VM alone was measured during the inspiratory phase in all studies.
Demonstrably, the VM alone increased IAP. Mean peak IAP from the VM alone varied considerably between studies and ranged from 3.8 to 38.8 kPa. There were insufficient data to examine training status and sex effects on IAP generation. However, one study showed a significantly higher IAP via the VM alone in experienced resistance trainers (27.1 ± 6.7 vs. 18.6 ± 4.9 kPa, respectively; p < 0.05) (28), whereas another study showed higher IAP via the VM alone in males versus females (38.7 ± 5.2 vs. 25.4 ± 3.3 kPa, respectively; p < 0.05) (14). Peak IAP from resistance exercise alone (8.7–21.5 kPa) was less than IAP generated from the VM alone (18.6–38.70 kPa) within 5 studies, where this comparison was possible (14,22,28,38,39). Significant differences between relative IAP (expressed relatively to the maximum IAP values attained from a VM alone) during a resistance exercise was found when sex and training status were considered. Males produced a lower relative IAP compared with females (54 ± 12% vs. 65 ± 12%) (p < 0.05) (14), whereas resistance-trained males produced a lower relative IAP during resistance exercises compared with untrained males (p < 0.05) (28).
IAP during resistance exercise was altered by the breathing behavior, that is, free breathing (normal breathing cycle) without performing the VM or with the VM. A higher IAP was observed with the VM than free breathing during resistance exercise. Nachemson et al. (40) found that the VM increased IAP compared with free breathing during lifting of 4-kg dumbbells while sitting (7.3 vs. 3.3 kPa) and during lifting of 8-kg dumbbells while standing (8.2 vs. 1.9 kPa). The VM also produced a more marked increased IAP compared with free breathing during isometric trunk flexion (12 vs. 10 kPa) and isometric trunk extension (10 vs. 8.5 kPa) (12).
The intensity of a lift and lifting to exhaustion impacted IAP during resistance exercise, with observed increases even when the VM was not instructed intentionally (22,28,51). Harman et al. (22) showed that IAP increased as the intensity of exercise increased from 50 to 100% of 4RM for the bench press, leg press, and dead lift. Similarly, during a standing isometric lift and the leg extension, IAP increased as the intensity increased up to 100% of maximal voluntary isometric contraction (28,51). The exercises that consistently produced the highest IAP were the squat, dead lift and leg press, whereas upper body exercises, such as the bench press, arm lift, and handgrip produced significantly lower IAP (22,38,51).
Is Performing the VM During Resistance Exercise a Safe Practice?
The database searches identified 10,573 articles. Review of their titles and abstracts revealed that 10,399 articles did not meet the inclusion/exclusion criteria. The full texts of the remaining 174 articles were reviewed for more detailed evaluation with the further exclusion of 152 articles. Based on the eligibility criteria, 22 articles were included in the final analysis. Eight studies reported the hemodynamic effects from the VM during resistance exercise. Five of these studies reported the hemodynamic effects from an instructed VM during resistance exercise, with blood pressure reported in 3 studies (31,41,42), whereas the other 2 studies reported cardiac output (26) and left ventricular function and wall stress (25). Three studies reported blood pressure from an unintentional VM during resistance exercise (34,35,43).
Blood pressure was found to be significantly higher during resistance exercise when performing a VM compared with free breathing. Narloch et al. (41) showed that during a 5RM leg press, mean blood pressure was greater with a VM (311/284 vs. 198/175 mm Hg) (p < 0.05), with similar results found by O'Connor et al. (42) and Linsenbardt et al. (31). Within the studies where an involunatary VM was performed, this occurred during heavy lifts (≥80% MVC) or lifts to volitional fatigue and resulted in augmentation of blood pressure (34,35,43). Augmented blood pressure paralleled rises in intrathoracic pressure (ITP) from the VM, with an initial rise of 1 mm Hg in systolic and diastolic blood pressure for each 1 Torr rise in ITP.
The VM did not alter left-ventricle wall stress or function in young men performing both submaximal and maximal lifts (25). Hughes et al. (26) also confirmed less extreme strain on the cardiovascular system when performing a VM during resistance exercise compared with a VM alone. The VM alone resulted in a 68 ± 4% fall in stroke volume compared with a fall of 42 ± 9% with the VM during resistance exercise. Heart rate and blood pressure responses were more stable for the VM during resistance exercise, whereas the VM alone produced a greater late-strain fall and poststrain overshoot in blood pressure with significant corresponding rise and fall in heart rate responses, respectively.
Adverse events were reported in 14 case studies and together included 19 patients (18 male patients and 1 female patient) aged between 14 and 64 years. The patients' levels of resistance training experience varied from 6 months to 2 years and were considered moderately trained (i.e., not performing advanced level resistance training and displaying levels of muscular strength similar to age-based norms). All patients were involved in resistance exercise when their adverse event occurred. Four reported incidents involved eye injury (Purtscher-like retinopathy, hemorrhage at macula, unilateral vision loss, and foveal hemorrhage) (6,17,29,44). Eight reported incidents involved the cerebrovascular system (subarachnoid and intracerebral haemorrhages, brainstem infarctions, and bilateral brain infarctions) (5,21,24,41,50), and 7 reported cases involved the lungs and chest wall (pneumomediastinum, sudden retrosternal pain, and spontaneous pneumothorax) (3,27,37,46,48). In all studies, it was speculated by the authors that the adverse event was secondary to elevated intracranial or intrathoracic or intra-abdominal pressures, as a consequence of a VM. All patients recovered after rest or medical intervention and returned to normal daily activities, but all were advised to avoid the VM when recommencing resistance training.
The purpose of this systematic review was to examine the extent and quality of current research literature, to evaluate the efficacy of the VM on increasing IAP, and the safety of performing the VM during resistance exercise. The present data provide evidence that the VM alone increases IAP and that the VM augments IAP during various resistance exercises, confirming our original hypothesis. Despite VM augmenting IAP during resistance exercise, peak IAP during the VM alone was consistently greater. Additionally, both resistance exercise intensity and effort affected IAP with incremental rises in IAP observed as exercise intensity and effort increased. The VM was associated with an increase in blood pressure during resistance exercise, confirming our original hypothesis. However, the VM alone was associated with greater hemodynamic changes compared to performing the VM during resistance exercise. From the available case studies that explicitly highlighted a link between adverse events and the VM during weightlifting, the data show that these were restricted to novice or moderately trained individuals. No such cases were documented in experienced (competitive) resistance trainers. Furthermore, although it was suggested that these events were a consequence of the VM associated with resistance exercise, it is unknown whether these patients used the VM in combination with resistance exercise or whether medical predisposition to the incidents/events existed.
The IAP generated from the VM alone was shown to vary considerably between the studies reviewed. However, these values were greater compared with the IAP of healthy adults at rest (converted from millimeters of mercury to kilopascals, lying supine: 0.2 ± 0.2 kPa, sitting: 2.7 ± 0.5 kPa, and standing: 2.2 ± 0.4 kPa), confirming the effectiveness of the VM for increasing IAP (9). The increased variability in IAP from the VM may be attributed to lung volumes and abdominal muscle strength. Greater lung volumes before the closing of the glottis have been shown to increase IAP resulting from the descending diaphragm acting on the relatively incompressible abdominal contents (19,20). Furthermore, contraction of the abdominal muscle, as occurs with the VM, markedly increases the IAP (11,12). Therefore, the data showing lower IAP from the VM alone in female versus male cohorts may reflect differences in lung size (thus lung volume) and abdominal muscle strength (14). The present cross-sectional data also show higher IAP from the VM alone in trained versus untrained individuals. This may partly reflect training-induced increases in abdominal strength, as alterations in abdominal strength are associated with changes in IAP generating capacity from the VM alone (11). Other factors that have been shown to affect IAP generation from the VM include measurement technique and posture (36). More than half the studies (9 of the 14 studies) measured IAP intragastrically through the use of a pressure transducer that is considered the gold standard. However, considerable variability has been reported for this technique, not only between individuals but also between laboratories (36). Changes in posture while performing the VM also affect IAP generation, possibly due to the abdominal muscle fiber length being suboptimal for producing the greatest tension (18). It is unlikely that changes in posture contributed to the large variation in IAP generated from the VM alone, as subjects were instructed to stand erect when performing the VM alone in all studies.
Intrathoracic pressure invariably increases when a VM is performed because it closely parallels IAP (22,43). Thus, increases in ITP/IAP detected during resistance exercises suggest the reflexive execution of the VM. MacDougall et al. (35) demonstrated incremental rises in ITP, recorded from mouth pressures, as the intensity of the leg press exercise increased at 80, 90, 95 and 100% 1RM. At 100% 1RM or as muscular failure was approached, mouth pressures reached values of 30–50 Torr. In a follow-up study, by continuously monitoring ITP directly, MacDougall et al. (34) established that the VM was unintentionally performed when the force output exceeded 80% MVC on the leg press. Furthermore, ITP increased with the intensity of the VM as muscular fatigue was approached (34). These findings provide evidence that the VM was reflexively activated during the resistance exercises performed at higher intensities (>80% MVC) within the studies where the VM was not actively instructed (22,28). The positive relationship between IAP and the intensity of resistance exercise (percentage MVC or RM)(22,28,51) likely suggests the involvement of the VM at higher intensities during resistance exercise.
The reflexive nature of the VM during resistance exercise is not surprising. The increased IAP offered by the VM can be thought of as the body's natural response to establish spine stability (8,28). The VM pressurizes the abdominal cavity through a combination of diaphragm and abdominal and pelvic floor muscle activity (11,12,18,20). Spine stability is important during exercises requiring high axial loading and may explain why peak IAP was greatest for leg exercises such as squats, dead lifts, and leg press (compared with upper body exercises, including bench press and arm curls). However, despite the VM augmenting IAP during resistance exercises, this review has shown that IAP generated seems to be lower than IAP generated from the VM alone. This may be attributed to the postures in which the resistance exercises were performed (18) or to the lower inspiratory volumes during the exercises (19,20,28). Males and resistance trained subjects were also shown to have a lower IAP relative to that achieved through a VM alone compared with females and untrained subjects during exercises at the same percentage of MVC (14,28). These observations suggest that spine stability may be achieved at a relatively lower IAP in resistance trainers who can generate greater IAP from a VM alone.
Blood pressure increase during resistance exercise was more marked with the VM than during free breathing and without engaging the VM (31,41,42). However, the present data show more extreme hemodynamic responses from the VM alone compared with the VM during resistance exercise. As discussed in a recent review on the cardiovascular effects of the VM, the depth and rate of the preceding breath and duration of strain are factors that affect the hemodynamic responses to the VM (33). Although the VM alone increases cardiovascular strain as a result of increased ITP (45), these effects are not exacerbated by combined resistance exercise. Hughes et al. (26) observed significant falls in cardiac output and blood pressure during the VM alone, which were attenuated during combined VM/handgrip exercise, suggesting lower cardiac strain. Additionally, performing the VM during resistance exercise has been shown to cause no alteration in left ventricular function and wall stress (25) and may prevent the development of left ventricular hypertrophy and risk of a cerebrovascular event as a result of decreasing transmural pressure (difference in pressure between 2 sides of the arterial wall) (23,30). Notably, lower blood pressure and heart rate responses were reported in experienced resistance trainers during exercises to volitional fatigue compared with novices (16). This observation in experienced trainers may be explained by their ability to avert extreme alterations in hemodynamics through tensing their diaphragms, thus preventing or minimizing elevations in ITP (1).
Despite an attenuated hemodynamic response when resistance training is associated with a VM, a clinical question remains as to its safety. Using only peer-reviewed cases is likely to underreport the total events associated with the VM during resistance exercise, and a thorough examination would require extensive review of medical records. In addition, 13 cases in experienced resistance trainers were excluded from the analysis because they may have been confounded by steroid use, which influences vascular changes that may predispose individuals to a hematoma during the VM (2). Furthermore, evidence is required to confirm whether an interaction exists between training status and risk of adverse events associated with the VM during resistance exercise. Lombardi and Troxel (32) reported that resistance training accounted for an estimated 268,096 hospital-reported injuries and 16 deaths in the United States from 1998 to 2001. Ninety-four percent of the deaths involved males, 78% occurred at home, and >50% involved the bench press. It is unknown what contributed to the deaths, although lifting heavy loads (which initiates the VM), as a risk factor, cannot be excluded as are other factors of congenital lesions, unknown cardiovascular risks, or undiagnosed hernia. A VM maintained for approximately >3 seconds during a lift can cause dizziness and fainting (10,45) because of the concomitant fall in systolic, diastolic, and pulse pressures.
The results of this review show that the VM performed during resistance exercise increases IAP, however, alterations in hemodynamics result, which may increase health risks in resistance trainers susceptible to cerebrovascular disease, cardiovascular disease, and hernias. Provided that individuals have a medical examination before engaging in resistance training to minimize health risks, strength and conditioning coaches can instruct resistance trainers to perform a brief VM (not exceeding 3 seconds) during a lift. This practice will effectively increase IAP and provide spinal stability, similar to the wearing of weight belts, and would likely lead toward improving lifting performance. The VM seems to be a naturally occurring reflexive response when lifting loads of high intensity, therefore, this practice should not be discouraged because this may reduce spinal stability during lifts such as the squats and increase the risk of lower back injuries. Furthermore, the VM during a resistance exercise should not be exaggerated because of the risk of dizziness and fainting. Given the lower hemodynamic responses seen in experienced resistance trainers compared to novices, training adaptations may reduce health and safety risks. Therefore, novice resistance trainers should start off training at lower intensities (where the VM is avoidable <80% 1RM and not lifting to volitional fatigue) and slowly progress to intensities where the VM is evoked. Future research is needed to directly investigate whether performing the VM during resistance exercise enhances the ability to lift loads and whether the increased IAP generated protects the structures of the lower back during a resistance exercise. Additionally, an extensive review and evaluation of medical records is needed to confirm the safety of its use during resistance exercise.
The results of the present study do not constitute endorsement of this practice by the authors or the National Strength and Conditioning Association.
1. Al-Bilbeisi FD, McCool FD. Diaphragm recruitment during nonrespiratory activities. Am J Resp Crit Care Med 162: 456–459, 2000.
2. Alaraj AM, Chamoun RB, Dahdaleh NS, Haddad GF, Comair YG. Spontaneous subdural haematoma in anabolic steroid dependent weight-lifters: reports of two cases and review of literature. Acta Neurochirurg 147: 85–88, 2005.
3. Asplund CA, Howard TM, O'Connor FG. Sponateous pneumomediastinum in a weightlifter. Curr Sports Med Rep 2: 63–64, 2003.
4. Baechle TR, Earle RW. Essentials of Strength Training and Conditioning. Champaign, IL: Human Kinetic, 2008.
5. Berrouschot J, Bormann A, Routsi D, Stoll A. Sports-related carotid artery dissection. Fortschritte der Neurologie-Psychiatrie 77: 528–531, 2009.
6. Chapman-Davies A, Lazarevic A. Valsalva maculopathy: case report. Clin Exp Optom 85: 42–45, 2002.
7. Cholewicki J, Ivancic PC, Radebold A. Can increased intra-abdominal pressure in humans be decoupled from trunk muscle co-contraction during steady state isometric exertions? J Appl Physiol 87: 127–133, 2002.
8. Cholewicki J, Juluru K, Radebold A, Panjabi MM, McGill SM. Lumbar spine stability can be augmented with an abdominal belt and/or increased intra-abdominal pressure. Eur Spine J 8: 388–395, 1999.
9. Cobb WS, Burns JM, Kercher KW, Matthews BD, Norton HJ, Heniford BT. Normal intra-abdominal pressure in healthy adults. J Surg Res 129: 231–235, 2005.
10. Compton D, Hill PM, Sinclair JD. Weight-lifters' blackout. Lancet 2: 1234–1237, 1973.
11. Cresswell AG, Blake PL, Thorstensson A. The effect of an abdominal muscle training program on intra-abdominal pressure. Scand J Rehab Med 26: 79–86, 1994.
12. Cresswell AG, Grundström H, Thorstensson A. Observations on intra-abdominal pressure and patterns of abdominal intra-muscular activity in man. Acta Physiol Scand 144: 409–418, 1992.
13. Daggfeldt K, Thorstensson A. The role of intra-abdominal pressure in spinal unloading. J Biomech 30: 1149–1155, 1997.
14. Essendrop M, Schibye B. Intra-abdominal pressure and activation of abdominal muscles in highly trained participants during sudden heavy trunk loads. Spine 29: 2445–2451, 2004.
15. Essendrop M, Schibye B, Hye-Knudsen C. Intra-abdominal pressure increases during exhausting back extension in humans. European Journal of Applied Physiology 87: 167–173, 2002.
16. Fleck SJ, Dean LS. Resistance-training experience and the pressor response during resistance exercise. J Appl Physiol 63: 116–120, 1987.
17. Gatzonis S, Charakidas A, Polchronopoulou Z, Brouzas D. Unilateral visual loss following bodybuilding training. Clin J Sport Med 14: 317–318, 2004.
18. Goldish GD, Quast JE, Blow JJ, Kuskowski MA. Postural effects on intra-abdominal pressure during Valsalva maneuver. Am J Phys Med Rehab 75: 324–327, 1994.
19. Hagins M, Pietrek M, Sheikhzadeh A, Nordin M. The effects of breath control on maximum force and IAP during a maximum isometric lifting task. Clin Biomech 21: 775–780, 2006.
20. Hagins M, Pietrek M, Sheikhzadeh A, Nordin M, Axen K. The effects of breath control on intra-abdominal pressure during lifting tasks. Spine 29: 464–469, 2004.
21. Hall-Jurkowski J, Sutton JR, Duke RJ. Subarachnoid hemorrhage in association with weight lifting attempts. Can J Sport Sci 8: 210, 1983.
22. Harman EA, Frykman PN, Clagett ER, Kraemer WJ. Intra-abdominal and intra-thoracic pressures during lifting and jumping. Med Sci Sports Exer 20: 195–201, 1988.
23. Haykowsky MJ, Eves ND, Warburton DE, Findlay MJ. Resistance exercises, the Valsalva maneuver, and cerebrovascular transmural pressure. Med Sci Sports Exer 35: 65–68 2003.
24. Haykowsky MJ, Findlay MJ, Ignaszewski AP. Aneurysmal subarachnoid hemorrhage associated with weight training: three case reports. Clin J Sport Med 6: 52–55, 1996.
25. Haykowsky MJ, Taylor D, Teo K, Quinney A, Humen D. Left ventricular wall stress during leg-press exercise performed with a brief Valsalva maneuver. Chest 119: 150–154, 2001.
26. Hughes LO, Heber E, Lahiri AM, Harries M, Raftery FB. Haemodynamic advantage of the Valsalva manoeuvre during heavy resistance training. Eur Heart J 10: 896–902, 1989.
27. Jones SI, Fred HL. Sudden retrosternal pain in a young weight lifter. Hosp Prac 32: 157–159, 1997.
28. Kawabata M, Shima N, Hamada H, Nakamura I, Nishizono H. Changes in intra-abdominal pressure and spontaneous breath volume by magnitude of lifting effort: highly trained athletes versus healthy men. Eur J Appl Physiol 109: 279–286, 2010.
29. Kocak N, Kaynak S, Oner H, Cingil G. Unilateral Purtscher-like retinopathy after weight-lifting. Eur J Ophthalmol 13: 395–397, 2003.
30. Lentini AC, McKelvie RS, McCartney N, Tomlinson CS, MacDougall JD. Left ventricular response in healthy young men during heavy-intensity weight-lifting exercise. J Appl Physiol 75: 2703–2710, 1993.
31. Linsenbardt S, Thomas TR, Madsen RW. Effect of breathing techniques on blood pressure response to resistance exercise. Brit J Sports Med 26: 97–100, 1992.
32. Lombardi VP, Troxel RK. U.S. injuries and deaths associated with weight training. Med Sci Sports Exer 35: S203, 2003.
33. Looga R. The Valsalva manoeuvre–cardiovascular effects and performance technique: a critical review. Respir Physiol Neurobiol 147: 39–49, 2005.
34. MacDougall JD, McKelvie RS, Moroz DE, Sale DG, McCartney N, Buick F. Factors affecting blood pressure during heavy weight lifting and static contractions. J Appl Physiol 73: 1590–1597, 1992.
35. MacDougall JD, Tuxen D, Sale DG, Moroz JR, Sutton JR. Arterial blood pressure response to heavy resistance exercise. J Appl Physiol 58: 785–790, 1985.
36. Malbrain ML. Different techniques to measure intra-abdominal pressure (IAP): time for a critical re-appraisal. Intensive Care Med 30: 357–371, 2004.
37. Marnejon T, Sarac S, Cropp AJ. Spontaneous pneumothorax in weightlifters. J Sports Med Phys Fitness 35: 124–126, 1995.
38. McGill SM, Sharratt MT. Relationship between intra-abdominal pressure and trunk EMG. Clin Biomech 5: 59–67, 1990.
39. Miyamoto K, Iinuma N, Maeda M, Wada E, Shimizu K. Effects of abdominal belts on intra-abdominal pressure, intra-muscular pressure in the erector spinae muscles and myoelectrical activities of trunk muscles. Clin Biomech 14: 79–87, 1999.
40. Nachemson AL, Andersson GBJ, Schultz AB. Valsalva maneuver biomechanics: effects on lumbar trunk loads of elevated intra-abdominal pressures. Spine 11: 476–479, 1986.
41. Narloch JA, Brandstater ME. Influence of breathing technique on arterial blood pressure during heavy weight lifting. Arch Phys Med Rehab 76: 457–462, 1995.
42. O'Connor P, Sforzo GA, Frye P. Effect of breathing instruction on blood pressure responses during isometric exercise. Phys Ther 69: 757–761, 1989.
43. Palanti P, Mos L, Munari L, Valle F, Del Torre M, Rossi A, Varotto L, Macor F, Martina S, Pessina AC, Dal Palu C. Blood pressure changes during heavy-resistance exercise. J Hypertension 7: S72–S73, 1989.
44. Pitta CG, Steinert R, Gragoudas ES, Regan CD. Small unilateral foveal hemorrhages in young adults. Am J Ophthalmol 89: 96–102, 1980.
45. Porth CJ, Bamrah VS, Tristani FE, Smith JJ. The Valsalva maneuver: mechanisms and clinical implications. Heart Lung 13: 507–518, 1984.
46. Sadarangani S, Patel DR, Pejka S. Spontaneous pneumomediastinum and epidural pneumatosis in an adolescent precipitated by weight lifting: a case report and review. Physician and Sportsmedicine 37: 147–153, 2009.
47. Shirley D, Hodges PW, Eriksson AE, Gandevia SC. Spinal stiffness changes throughout the respiratory cycle. J Appl Physiol 95: 1467–1475, 2003.
48. Simoneax SF, Murphy BJ, Tehranzadeh J. Spontaneous pneumothorax in a weight lifter: a case report. Am J Sports Med 18: 647–648, 1990.
49. Swain DP, Leutholtz BC. Exercise Prescription: A Case Study Approach to the ACSM Guidelines. Champaign, IL: Human Kinetics, 2007.
50. Tuxen DV, Sutton J, MacDougall D, Sale D. Brainstem injury following maximal weight lifting attempts. Med Sci Sports Exer 15: 158, 1983.
51. Williams CA, Lind AR. The influence of straining maneuvers on the pressor response during isometric exercise. Eur J Appl Physiol 56: 230–237, 1987.
52. Williams MA, Haskell WL, Ades PA, Amsterdam EA, Bittner V, Franklin B, Gulanick M, Laing ST, Stewart KJ. Resistance exercise in individuals with and without cardiovascular disease: 2007 update a scientific statement from the American heart association council on clinical cardiology and council on nutrition, physical activity, and metabolism. Circulation 116: 572–584, 2007.
53. Zatsiorsky VM. Science and Practice of Strength Training. Champiagn, IL: Human Kinetics, 1995.