The effects of breath control on maximum force and IAP during a maximum isometric lifting task

Interaction of breathing pattern and posture on abdominal muscle activation and intra-abdominal pressure in healthy individuals: a comparative cross-sectional study

We aimed to assess the effects of interaction between several breathing patterns and postures on abdominal muscle activation and intra-abdominal pressure (IAP). This comparative cross-sectional study enrolled fourteen healthy university students majoring in sports science and/or physical education. They performed four active breathing tasks: quiet nasal breathing (Q-Bre), nasal deep breathing (Deep-Bre), completely forced expiration (Forced-Expi), and exertional nasal inhalation with abdominal muscles with isometric contraction (Exertion-Inspi) in the elbow-toe plank and supine postures. Breathing volume; IAP; and transverse abdominis-internal oblique muscle (TrA-IO) and external oblique muscle (EO) activities were recorded. Abdominal muscle activity and IAP significantly interacted with breathing pattern and postures during the expiratory phase (p < 0.05). In the inspiratory phase, TrA-IO activity was significantly affected by breathing pattern and EO activity with posture (p < 0.05). TrA-IO activity significantly increased during Forced-Expi in the supine posture (47.6% of the maximum voluntary contraction) and Exertion-Inspi in the elbow-toe posture (35.7%), whereas no differences were found during Deep-Bre or Q-Bre (< 20%). EO activity increased in the elbow-toe posture (22.5-30.6%) compared with that in the supine posture (< 5%) during all breathing tasks. IAP values were low during all tasks (< 15%) except for Forced-Expi (24.9%). Abdominal muscle activation and IAP interacted with the breathing pattern and posture.

Intrinsic factors contributing to elevated intra-abdominal pressure

Pelvic floor disorders affect 24% of US women, and elevated intra-abdominal pressure may cause pelvic injury through musculoskeletal strain. Activity restrictions meant to reduce pelvic strain after traumatic events, such as childbirth, have shown little benefit to patients. Reported high variability in abdominal pressure suggests that technique plays a substantial role in pressure generation. Understanding these techniques could inform evidence-based recommendations for protective pelvic care. We hypothesized use of a motion-capture methodology could identify four major contributors to elevated pressure: gravity, acceleration, abdominal muscle contraction, and respiration. Twelve women completed nineteen activities while instrumented for whole body motion capture, abdominal pressure, hip acceleration, and respiration volume. Correlation and partial least squares regression were utilized to determine primary technique factors that increase abdominal pressure. The partial least squares model identified two principal components that explained 59.63% of relative intra-abdominal pressure variability. The first component was primarily loaded by hip acceleration and relative respiration volume, and the second component was primarily loaded by flexion moments of the abdomen and thorax. While reducing abdominal muscle use has been a primary strategy in protective pelvic floor care, the influence of hip acceleration and breathing patterns should be considered with similar importance in future work.

Effect of Valsalva Maneuver by Heavy Weight Lifters on Ear and Its Attributes

It is observed that people hold their breath while heavy weight lifting to get extra strength. Holding the breath during weight lifting can lead to abnormal increase in middle ear pressure which can lead to several hearing/auditory complications. The objective of the study was to investigate the impact of heavy weightlifting on various parameters related to ears like blocking sensation, tinnitus, vertigo, headache and temporary threshold shift across light and heavy weightlifters, as amateur weightlifting among youth is rapidly increasing. A cross-sectional survey design was used in this study. Based on the random sampling strategy, 40 participants in the age range of were selected across various gyms in Gurgaon India. The participants were equally divided into two categories; light weigh-lifters (LWL) who lifted half of the body weight and heavy weightlifters (HWL) who lifted equal or more than the body weight. A questionnaire was developed, validated and administered which consists of 23 questions targeting blocking sensation, tinnitus, vertigo, temporary threshold shift and headache. Chi-square analysis revealed that higher proportion of HWL group experienced blocking sensation (65% vs 25%), tinnitus (70% vs 35%), vertigo (75% vs 40%), headache (80% vs 35%), and temporary threshold shift (60% vs 35%) then the LWL group. Strenuous exercises like heavy weight lifting can lead to various ear problems such as blocking sensation, temporary threshold shift, tinnitus, and vertigo, which, may lead to hearing loss.

Relationship of heart rate, perceived exertion, and intra-abdominal pressure in women

Background

Exercise increases intra-abdominal pressure (IAP) acutely, which may impact the pelvic floor of women. IAP during exercise demonstrates high variability among women but is not routinely assessed. Assessing less invasive measures related to IAP during exercise may facilitate study of how IAP impacts the pelvic floor.

Methods

The objective of this study was to investigate the relationship of heart rate and rating of perceived exertion (RPE) with IAP during a standard treadmill test. We describe the trend of IAP by predicted aerobic fitness during incremental exercise. IAP was measured using a validated transducer placed in the upper vagina. Heart rate and RPE were collected during the first 3 stages of the standard Bruce treadmill protocol. Relationships of heart rate and RPE with IAP were determined by Pearson correlation coefficients. Predicted aerobic fitness values for each participant were ranked in tertiles with IAP by treadmill stage.

Results

Twenty-four women participated in this study (mean age: 24.7 (5.4) years; body mass index: 22.5 (2.2) kg/m²). There were significant relationships between heart rate and IAP (r= 0.67, p < 0.001) and RPE and IAP (r= 0.60, p < 0.001) across treadmill stages. Tertiles of predicted aerobic fitness and IAP displayed similar trends as other exercise measures during incremental exercise, such as, heart rate and ventilation.

Conclusion

Heart rate and RPE could be used as proxy measures of IAP during incremental exercise. Aerobic fitness may help explain IAP variability in women and provide context for future research on IAP and pelvic floor health.

Postural and respiratory function of the abdominal muscles: A pilot study to measure abdominal wall activity using belt sensors

BACKGROUND: The abdominal muscles play an important respiratory and stabilization role, and in coordination with other muscles regulate intra-abdominal pressure (IAP) to stabilize the spine. OBJECTIVE: To examine a new, non-invasive method to measure activation of the abdominal wall and compare changes in muscle activation during respiration while breathing under a load, and during instructed breathing. METHODS: Thirty-five healthy individuals completed this observational crossover study. Two capacitive force sensors registered the abdominal wall force during resting breathing stereotype, instructed breathing stereotype and under a load. RESULTS: Mean abdominal wall force increased significantly on both sensors when holding the load compared to resting breathing (Upper Sensor: P< 0.0005, d=-0.46, Lower Sensor: P< 0.0005, d=-0.56). The pressure on both sensors also significantly increased during instructed breathing compared to resting breathing (US: P< 0.0005, d=-0.76, LS: P< 0.0005, d=-0.78). CONCLUSIONS: The use of capacitive force-sensors represent a new, non-invasive method to measure abdominal wall activity. Clinically, belts with capacitive force sensors can be used as a feedback tool to train abdominal wall activation.

Does Intra-abdominal Pressure Have a Causal Effect on Muscle Strength of Hip and Knee Joints?

ABSTRACT

Tayashiki, K, Kanehisa, H, and Miyamoto, N. Does intra-abdominal pressure have a causal effect on muscle strength of hip and knee joints? J Strength Cond Res 35(1): 41-46, 2021-It remains unclear whether intra-abdominal pressure (IAP) has a causal effect on lower-limb muscle strength. This study aimed to clarify whether or not changes in IAP, induced by changing breathing state, influence muscle strength of hip and knee extensor and flexor. Eighteen healthy males (age: 22.0 ± 2.2 years, height: 1.71 ± 0.03 m, and body mass: 68.1 ± 6.1 kg) performed maximal voluntary isometric contractions (MVICs) of hip and knee extensor and flexor during breath-hold at full inspiration (inspiratory condition) or expiration (expiratory condition), or during normal breath-hold (normal condition). Intra-abdominal pressure was obtained by a pressure transducer placed in the rectum and determined at the time at which the developed torque reached to the maximum. The IAP during each MVIC was significantly greater in inspiratory condition than in expiratory condition (p < 0.05). The maximal torque of hip extensor was significantly greater in inspiratory condition than in expiratory condition (p < 0.05). By contrast, the maximal torque of each of hip flexor, knee extensor, and knee flexor was not different among the 3 breath-hold conditions. The IAP was significantly correlated with the maximal torque of hip extensor in each breath-hold condition. The current results suggest that a sufficient increase in IAP has a causal effect to specifically improve muscle strength of hip extensor.

Risk Factors for Retinal Detachment: A Case-Control Study

OBJECTIVE

The aim of this study was to investigate risk factors for retinal detachment or tear (RD/T), and follow up two studies that found increased risk from work-related heavy lifting.

METHODS

We conducted a case-control study including 200 cases of RD/T and 415 controls. Participants completed a questionnaire covering general health, vision, and physical exertion. Multiple logistic regression and propensity score matching was used to control confounding and estimate independent effects.

RESULTS

RD/T risk was increased by one lifting measure: current regular lifting of more than 30 lbs (>13.6 kg). In the population aged less than 65 years, the odds ratio comparing those with/without heavy lifting was 1.81, 95% confidence interval = 1.08 to 3.04.

CONCLUSION

Occupational heavy lifting may represent a risk factor for RD/T, but further research is needed in populations with frequent heavy physical exertion to more precisely quantify the risk.

Causal effect of intra-abdominal pressure on maximal voluntary isometric hip extension torque

PURPOSE

Intra-abdominal pressure (IAP) has been recently shown to be associated specifically with maximal voluntary isometric contraction (MVC) torque of hip extension, although the causal relationship remains unclear. The present study aimed to elucidate whether IAP has a causal effect on hip extension MVC torque.

METHODS

IAP during hip extension MVC was changed by controlling the lung volume (i.e., depth of inspiration). Twelve healthy males conducted MVCs of hip extension during breath-hold at full inspiration (inspiratory condition) or expiration (expiratory condition), or during normal breath-hold (normal condition). IAP during MVCs was measured a pressure transducer placed in the rectum.

RESULTS

The IAP during hip extension MVC was significantly higher in inspiratory condition (132.0 ± 46.1 mmHg) than in the other two conditions and also higher in normal condition (104.6 ± 35.9 mmHg) than in expiratory condition (77.0 ± 39.1 mmHg). The hip extension MVC torque was significantly higher in inspiratory condition (297.7 ± 82.7 N m) than in expiratory condition (266.4 ± 84.5 N m). In each condition, the hip extension MVC torque correlated with IAP during the MVC task.

CONCLUSION

The current results suggest that IAP has a positive causal effect on hip extension MVC torque and that a sufficient increase in IAP directly leads to an enhancement of hip extension MVC torque.

Associations of maximal voluntary isometric hip extension torque with muscle size of hamstring and gluteus maximus and intra-abdominal pressure

PURPOSE

Muscle size of the hamstring and gluteus maximus (GM) as well as intra-abdominal pressure (IAP) are considered as factors affecting the torque development during hip extension. This study examined the associations of torque development during maximal voluntary isometric hip extension with IAP and muscle size of the hamstring and GM.

METHODS

Anatomical cross-sectional area (ACSA) of the hamstring and thickness of GM were determined in 20 healthy young males using an ultrasonography apparatus (Experiment 1). Torque and IAP were simultaneously measured while subjects performed maximal voluntary isometric hip extension. The IAP was measured using a pressure transducer placed in the rectum and determined at the time at which the developed torque reached to the maximal. In Experiment 2, torque and IAP were measured during maximal voluntary isometric hip flexion in 18 healthy young males.

RESULTS

The maximal hip extension torque was significantly correlated with the IAP (r = 0.504, P = 0.024), not with the ACSA of the hamstring (r = 0.307, P = 0.188) or the thickness of GM (r = 0.405, P = 0.076). The relationship was still significant even when the ACSA of the hamstring and the thickness of GM were adjusted statistically (r = 0.486, P = 0.041). The maximal hip flexion torque was not significantly correlated with the IAP (r = -0.118, P = 0.642).

CONCLUSION

The current results suggest that IAP can contribute independently of the muscle size of the agonists to maximal voluntary hip extension torque.

The Valsalva manoeuvre: physiology and clinical examples

The Valsalva manoeuvre (VM), a forced expiratory effort against a closed airway, has a wide range of applications in several medical disciplines, including diagnosing heart problems or autonomic nervous system deficiencies. The changes of the intrathoracic and intra-abdominal pressure associated with the manoeuvre result in a complex cardiovascular response with a concomitant action of several regulatory mechanisms. As the main aim of the reflex mechanisms is to control the arterial blood pressure (BP), their action is based primarily on signals from baroreceptors, although they also reflect the activity of pulmonary stretch receptors and, to a lower degree, chemoreceptors, with different mechanisms acting either in synergism or in antagonism depending on the phase of the manoeuvre. A variety of abnormal responses to the VM can be seen in patients with different conditions. Based on the arterial BP and heart rate changes during and after the manoeuvre several dysfunctions can be hence diagnosed or confirmed. The nature of the cardiovascular response to the manoeuvre depends, however, not only on the shape of the cardiovascular system and the autonomic function of the given patient, but also on a number of technical factors related to the execution of the manoeuvre including the duration and level of strain, the body position or breathing pattern. This review of the literature provides a comprehensive analysis of the physiology and pathophysiology of the VM and an overview of its applications. A number of clinical examples of normal and abnormal haemodynamic response to the manoeuvre have been also provided.

Breathing Techniques Affect Female but Not Male Hip Flexion Range of Motion

Two protocols were undertaken to help clarify the effects of breathing techniques on hamstrings (hip flexion) range of motion (ROM). The protocols examined effects of breathing conditions on ROM and trunk muscle activity. Protocol 1: Thirty recreationally active participants (15 male, 15 female, 20-25 years) were monitored for changes in single-leg raise (SLR) ROM with 7 breathing conditions before or during a passive supine SLR stretch. Breathing conditions included prestretch inhale, prestretch exhale, inhale-during stretch, exhale-during stretch, neutral, hyperventilation, and hypoventilation before stretch. Protocol 2: Eighteen recreationally active participants (9 male, 9 female, 20-25 years) were monitored for electromyographic (EMG) activity of the rectus abdominus, external obliques, lower abdominal stabilizers, and lower erector spinae while performing the 7 breathing conditions before or during a passive SLR stretch. Control exhibited less ROM (p = 0.008) than the prestretch inhale (7.7%), inhale-during stretch (10.9%), and hypoventilation (11.2%) conditions with females. Protocol 3: Greater overall muscle activity in the prestretch exhale condition was found compared with inhale-during stretch (43.1%↓; p = 0.029) and hypoventilation (51.2%↓; p = 0.049) conditions. As the inhale-during stretch and hypoventilation conditions produced the lowest levels of muscle activity for both sexes and the highest ROM for the females, it can be assumed that both mechanical and neural factors affect female SLR ROM. Lesser male ROM might be attributed to anatomical differences such as greater joint stiffness. The breathing techniques may have affected intra-abdominal pressure, trunk muscle cocontractions, and sympathetic neural activity to enhance female ROM.

Regular change in spontaneous preparative behaviour on intra-abdominal pressure and breathing during dynamic lifting

PURPOSE

Intra-abdominal pressure (IAP) and breathing behaviour are important preparative pre-lifting actions for functional stability during lifting. This study aimed to examine spontaneous changes in the peak rate of IAP development (Rate-IAP), peak IAP (Peak-IAP), the time of Rate- and Peak-IAP occurrence and respiratory volume in response to dynamic load lifting.

METHODS

Eleven healthy men performed quick dynamic deadlifting using 30, 45, 60 and 75% of the isometric maximal lifting effort (iMLE). IAP was measured using an intrarectal pressure transducer. The spontaneous respiratory volume was calculated from air flow data using pneumotachography. The lifting motion onset was determined from the hip joint motion using an electrogoniometer.

RESULTS

From 30 to 75% of the iMLE, Rate-IAP occurred early from 2 ± 28 to -179 ± 16 ms (P < 0.01), whereas Peak-IAP occurred late from 165 ± 31 to 82 ± 23 ms (P = 0.12) relative to the lifting motion onset. Rate-IAP increased from 224 ± 47 to 507 ± 69 mmHg/s (P < 0.01), whereas Peak-IAP increased from 37 ± 8 to 90 ± 11 mmHg (P < 0.01) at 30-75% of the iMLE. Rate-IAP strongly correlated with Peak-IAP at each lifting load (r = 0.94-0.97). Relative to the resting tidal volume, the inspiratory volume during pre-lifting significantly increased above 60% of the iMLE, whereas expiratory volume significantly decreased at all lifting loads.

CONCLUSIONS

Preparative pre-lifting behaviours alter IAP and breathing and are co-ordinated by the lifting load magnitude. These behaviours appear to be functionally important for dynamic lifting.

Grunting in tennis increases ball velocity but not oxygen cost

Grunting is widely used by professional tennis players, but no research has been done to verify enhanced performance with grunting. Therefore, the purpose of this study was to determine if grunting enhanced ball velocity in groundstrokes and secondly, to determine if grunting increased the physiological cost of hitting (VO2, HR, VE/VO2, and RPE). Participants were 10 members of the men's (n = 5) and women's (n = 5) tennis teams at a Division I university who had just completed their indoor competitive season. Two hitting sessions were used as players repetitively hit forehand and backhand shots while either grunting or not grunting. Each hitting session consisted of five 2-minute periods with a 1-minute break in between each period. Ball velocity was measured with a radar gun. During each hitting session, players wore a portable metabolic measuring unit. HR was monitored using a Polar monitor, and RPE was assessed using Borg's 6-20 scale. Grunting increased ball velocity (kph) 3.8% compared with non-grunting condition (p < 0.034) with the mean ± SD being 83.4 ± 0.6.1 and 80.3 ± 0.8.7, respectively. The physiological responses (VO2, HR, VE/VO2, and RPE) for the 2 hitting conditions were not significantly different for any variable. When averaged across both hitting conditions, HR over the 5-time periods was higher in periods 3-5 than period (p < 0.018) 1, whereas VE/VO2 and RPE were greater in periods 2-5 than period 1 (p = 0.001). RPE significantly increased over time with periods 2-5 being greater than period 1 (p = 0.001). It was concluded that grunting increased ball velocity without increasing VO2 or VE/VO2 or RPE in comparison with not grunting. It may be worthwhile for players and coaches in tennis and other sports to experiment with grunting to determine possible improvement in performance.

The Valsalva maneuver: its effect on intra-abdominal pressure and safety issues during resistance exercise

During resistance exercise, a brief Valsalva maneuver (VM) is unavoidable when lifting heavy loads (>80% of maximal voluntary contraction) or when lifting lighter loads to failure. It has been proposed that the performance of the VM during resistance exercise increases the stability of the spine because of augmented intra-abdominal pressure (IAP). However, resistance trainers are often advised to avoid the VM during resistance exercise because of potential adverse vascular events. The aim of this review was to establish the effect of the VM on IAP and to evaluate if the VM during resistance exercise is a safe practice. Relevant databases were searched to examine the effect of the VM on: (a) IAP and (b) hemodynamics during resistance exercise and reported adverse events. The data show that the VM alone increases IAP and that the VM augment IAP during various resistance exercises. An incremental rise in IAP was observed as the lifting intensity and effort increased, with IAP tending to be lower compared with peak IAP from the VM alone. The VM was associated with an increase in blood pressure during resistance exercise, but the VM alone was associated with greater hemodynamic changes. In conclusion, the VM effectively increases IAP, which may assist with spine stability and trunk rigidity during resistance exercise. The health risks associated with the VM during resistance exercise remain unconfirmed.

Coordination of breathing with nonrespiratory activities

Many articles in this section of Comprehensive Physiology are concerned with the development and function of a central pattern generator (CPG) for the control of breathing in vertebrate animals. The action of the respiratory CPG is extensively modified by cortical and other descending influences as well as by feedback from peripheral sensory systems. The central nervous system also incorporates other CPGs, which orchestrate a wide variety of discrete and repetitive, voluntary and involuntary movements. The coordination of breathing with these other activities requires interaction and coordination between the respiratory CPG and those governing the nonrespiratory activities. Most of these interactions are complex and poorly understood. They seem to involve both conventional synaptic crosstalk between groups of neurons and fluid identity of neurons as belonging to one CPG or another: neurons that normally participate in breathing may be temporarily borrowed or hijacked by a competing or interrupting activity. This review explores the control of breathing as it is influenced by many activities that are generally considered to be nonrespiratory. The mechanistic detail varies greatly among topics, reflecting the wide variety of pertinent experiments.

Breath control during a tiptoe task

Examination of naturally occurring respiration during postural challenges may increase our understanding of the factors linking respiration to lumbar segmental control. This study determined if the timing and magnitude of inhaled volume changes were related to mechanical events that challenge spinal stability during a tiptoe task. Thirty healthy individuals (15 male) had airflow recorded while they completed a tiptoe task which involved: moving onto tiptoe while reaching toward a hanging target (ascent); grasping and holding the target while maintaining the tiptoe position for 3 s (hold); and then returning to the start position (descent). The rate of airflow and amount of inhaled volume (normalized to vital capacity (%VC)) were identified at 13 different intervals spanning the ascent, hold and descent phase. Using repeated measures analysis of variance, significant main effects were identified for both rate of airflow (p < 0.001) and %VC (p < 0.001). Exploration of these main effects revealed that individuals tended to inspire and increase %VC during the ascent phase, hold their breath and maintain %VC during the hold phase when whole body balance is challenged, and exhale during the descent phase. These findings are congruent with theories suggesting that breath control is linked in predictable ways to potentially improve lumbar spine stiffness when presented with mechanical challenges during functional tasks.

Effect of airway control by glottal structures on postural stability

Maintenance of upright posture involves complex neuromotor processes that include control of thoracic and abdominal pressures. Control of airflow by glottal structures is a primary determinant of thoracic pressure and may have a role in control of postural stability. This study aimed to investigate the effect of modulation of airway control on upright postural stability during postural perturbations. Standing balance was gently perturbed in the sagittal plane during 7 breathing/voicing tasks that ranged from completely closed (breath-hold), to partially opened (voicing) or completely open (sigh) glottal conditions in 11 healthy adults. Dependent measures were peak amplitude of displacement of the thorax and center of pressure (CoP). When the glottis was completely open during sigh, thoracic displacement in response to the perturbation was greater than in all other conditions, regardless of direction of perturbation (post hoc, all P < 0.002). The absolute amplitude of CoP displacement was greater with backward perturbation (main effect, Direction P = 0.001) and was greater at both extremes of glottal modulation (glottis closed and completely open) than when the glottis was partially opened during counting out loud (post hoc, all P < 0.04). These results show that airway modulation affects postural control during upright perturbations. The thorax was more stable when the glottis was engaged than when it was required to remain open, whereas control of CoP displacement appeared more optimal during the natural dynamic mid-range airway modulation of voicing. These data suggest that glottal control influences balance, and that glottal control strategies may be an important consideration for patients with breathing and/or balance disorders.

'The core': understanding it, and retraining its dysfunction

"Core stability training" is popular in both the therapeutic and fitness industries but what is actually meant and understood by this concept? And does everyone need the same training approach? This paper examines the landscape of 'the core' and its control from both a clinical and research perspective. It attempts a comprehensive review of its healthy functional role and how this is commonly changed in people with spinal and pelvic girdle pain syndromes. The common clinically observable and palpable patterns of functional and structural change associated with 'problems with the core' have been relatively little described. This paper endeavors to do so, introducing a variant paradigm aimed at promoting the understanding and management of these altered patterns of 'core control'. Clinically, two basic subgroups emerge. In light of these, the predictable difficulties that each group finds in establishing the important fundamental elements of spino-pelvic 'core control' and how to best retrain these, are highlighted. The integrated model presented is applicable for practitioners re-educating movement in physiotherapy, rehabilitation, Pilates, Yoga or injury prevention within the fitness industry in general.

EMG and kinematics analysis of the trunk and lower extremity during the sit-to-stand task while wearing shoes with different heel heights in healthy young women

This study investigated the EMG characteristics and the kinematics of the trunk and lower extremity during the sit-to-stand (STS) task while wearing 1-, 4-, and 8-cm high-heeled shoes. We examined differences in the EMG data of the internal oblique, erector spinae, medial hamstring, and rectus femoris muscles during the STS task. The motion of the hip joint during an STS task was measured with a NorAngle Electrogoniometer System. Twelve young healthy women were recruited to this study. EMG characteristics and the hip joint angle were recorded during the performance of an STS task by subjects wearing high-heeled shoes of three different heel heights. The muscle onset time and EMG activity during this task were analyzed. In 8-cm high-heeled shoes, the onset time for the erector spinae muscle was significantly delayed, and the onset latency for the medial hamstring and the rectus femoris was significantly decreased. There was increased activity in the erector spinae and rectus femoris muscle during this task when wearing 8-cm high-heeled shoes. The initial hip flexion angle at the start point of the STS task did not differ among the 1-, 4-, and 8-cm heel-height conditions, but the trunk flexion angle, corresponding to the displacement between the peak hip flexion and initial hip flexion, was significantly larger in the 8-cm heel-height condition than in the 1- and 4-cm heel-height conditions. The findings suggest that excessive heel height has the potential to induce muscle imbalance during the STS task.

The valsalva maneuver revisited: the influence of voluntary breathing on isometric muscle strength

We assessed the effects of 4 voluntary breathing conditions on maximal voluntary isometric force of large muscle groups. Ten subjects performed maximum voluntary isometric contractions (MVICs) of knee flexion and extension, shoulder abduction and adduction, and elbow flexion and extension under all breathing conditions: normal breathing, forced inhalation, forced exhalation, and the Valsalva maneuver (VM). Forced exhalation significantly increased peak force during shoulder adduction, elbow extension, and knee extension MVIC tasks (p = 0.001, 0.024, and 0.002, respectively); the peak force during the Valsalva maneuver was not different from forced exhalation for all tested muscle groups. No voluntary breathing condition seemed to influence the peak force during the knee flexion, elbow flexion, and shoulder abduction MVIC tasks. The results demonstrate that voluntary breathing imposes a significant impact on isometric muscle strength. Given the increased cardiovascular risks associated with the Valsalva maneuver, it is highly recommended that forced exhalation be used during exercise at maximal levels, especially in repetitive repetitions.