Musculoskeletal Morphology and Joint Flexibility-Associated Functional Characteristics across Three Time Points during the Menstrual Cycle in Female Contemporary Dancers.

Findings are inconsistent with regards to whether menstrual cycle phase-associated changes in physical functioning exist. It is possible that such discrepancies are due to varying rigour in experimental approaches. The current study aimed to systematically evaluate any effect of carefully tracked menstrual cycle phase on precisely measured muscle structure and function in a physically active group (contemporary dancers). Eleven women aged (M [SD]) 23.5 [2.94] years, undergoing 10.5 [1.73] hours of contemporary dance practice and 6.12 [2.36] hours of other physical activity per week, were recruited. Sex hormone level (enzyme-linked immunosorbent assays (ELISA), skin temperature and ovulation kits), physical pain assessments (Ice Water Test, Visual Analogue Scale, The Physical Activity Readiness Questionnaire, Self-Estimated Functional Inability Because of Pain Questionnaire, and Pain Anxiety Symptoms Scale), muscle architecture measurement (B-mode ultrasonography), and physical functioning (dynamometry, force-platform and electromyography) on both lower limbs were measured at three time points during one cycle, following three months of menstrual cycle monitoring. There was no difference in musculoskeletal flexibility variables between follicular, ovulatory, or luteal phases. Nonetheless, oestrogen change was associated with variability in 11 musculoskeletal variables, progesterone change was associated with variability in 7, and relaxin change was associated with variability in 15. Negative correlations existed between progesterone and flexibility and between oestrogen and jump variables. Moreover, oestrogen and relaxin were associated with increased musculoskeletal compliance, whilst progesterone was associated with increased muscle stiffness. In short, in absolute sex hormone levels, 'inter-individual' variances appear more impactful than 'intra-individual' variances. Not only are oestrogen and progesterone associated with differing musculoskeletal outcomes, but relaxin is also associated with musculoskeletal compliance changes. These effects are anticipated to impact jump height and flexibility, and hence, they could be expected to affect overall physical performance, including dance.

Physiotherapist-led exercise versus usual care (waiting-list) control for patients awaiting rotator cuff repair surgery: A pilot randomised controlled trial (POWER).

BACKGROUND: Once a decision to undergo rotator cuff repair surgery is made, patients are placed on the waiting list. It can take weeks or months to receive surgery. There has been a call to move from waiting lists to 'preparation' lists to better prepare patients for surgery and to ensure it remains an appropriate treatment option for them. OBJECTIVE: To evaluate the feasibility, as measured by recruitment rates, treatment fidelity and follow-up rates, of a future multi-centre randomised controlled trial to compare the clinical and cost-effectiveness of undertaking a physiotherapist-led exercise programme while waiting for surgery versus usual care (waiting-list control). DESIGN: Two-arm, multi-centre pilot randomised controlled trial with feasibility objectives in six NHS hospitals in England. METHOD: Adults (n = 76) awaiting rotator cuff repair surgery were recruited and randomly allocated to a programme of physiotherapist-led exercise (n = 38) or usual care control (n = 38). RESULTS: Of 302 eligible patients, 76 (25%) were randomised. Of 38 participants randomised to physiotherapist-led exercise, 28 (74%) received the exercise programme as intended. 51/76 (67%) Shoulder Pain and Disability Index questionnaires were returned at 6-months. Of 76 participants, 32 had not received surgery after 6-months (42%). Of those 32, 20 were allocated to physiotherapist-led exercise; 12 to usual care control. CONCLUSIONS: A future multi-centre randomised controlled trial is feasible but would require planning for variable recruitment rates between sites, measures to improve treatment fidelity and opportunity for surgical exit, and optimisation of follow-up. A fully powered, randomised controlled trial is now needed to robustly inform clinical decision-making.

No Effect of Interset Palm Cooling on Acute Bench Press Performance, Electromyography Amplitude, or Spectral Frequencies in Resistance-Trained Men.

ABSTRACT: McMahon, G, Kennedy, R, and Burden, A. No effect of interset palm cooling on acute bench press performance, electromyography amplitude or spectral frequencies in resistance-trained men. J Strength Cond Res 37(3): 555-563, 2023-Previous research has suggested that cooling distal to the working agonist muscles during the interset rest periods of high-intensity resistance exercise may facilitate improved performance through increased agonist activation. However, these studies have used inappropriate electromyography (EMG) normalization techniques. Therefore, the aim of this study was to compare 2 palm-cooling conditions with a thermoneutral condition during high-intensity resistance exercise and subsequent effects on exercise performance, EMG amplitude, and spectral frequencies using appropriate normalization methodologies. Eleven healthy, resistance-trained, young men (20-36 years old) performed 4 sets of bench press exercise to exhaustion at 80% 1RM each separated by 3 minutes of passive recovery. Palm-cooling (10° C [TEN] or 15° C [FTN]) or thermoneutral (28° C [CON]) conditions were applied for 60 seconds during the recovery interval of each set in a randomized, double-blind fashion, with 4 days of recovery between experimental conditions. Palm temperature was significantly lower (p < 0.05) in the TEN and FTN conditions compared with CON. Number of repetitions and mean power in the bench press declined significantly after each set in all conditions (p < 0.05). There were no significant differences (p > 0.05) in any bench press performance or EMG-related variables between any of the conditions. Palm cooling at either 10 or 15° C had no effects on bench press performance compared with a thermoneutral condition, with no observable effects on neuromuscular responses during exercise. Therefore, cooling is not currently recommended as an ergogenic strategy to enhance acute bench press performance during high-intensity resistance training.

Circulating Tumor Necrosis Factor Alpha May Modulate the Short-Term Detraining Induced Muscle Mass Loss Following Prolonged Resistance Training.

INTRODUCTION: Tumor necrosis factor alpha (TNFα) is a pro-inflammatory cytokine that has been shown to modulate muscle mass, and is responsive to exercise training. The effects of resistance training (RT) followed by a short period of detraining on muscle size, architecture and function in combination with circulating TNFα levels have not been previously investigated in a young, healthy population. METHODS: Sixteen participants (8 males and 8 females) were randomly assigned to a training group (TRA; age 20 ± 3 years, mass 76 ± 7 kg), whilst fourteen participants (7 males and 7 females) age 22 ± 2 years, mass 77 ± 6 kg were assigned to a control group (CON). Measures of vastus lateralis (VL) muscle size (normalized physiological cross-sectional area allometrically scaled to body mass; npCSA), architecture (fascicle length; LF, pennation angle Pθ), strength (knee extensor maximal voluntary contraction; KE MVC), specific force, subcutaneous fat (SF) and circulating TNFα were assessed at baseline (BL), post 8 weeks RT (PT), and at two (DT1) and four (DT2) weeks of detraining. RESULTS: Pooled BL TNFα was 0.87 ± 0.28 pg/mL with no differences between groups. BL TNFα tended to be correlated with npCSA (p = 0.055) and KEMVC (p = 0.085) but not specific force (p = 0.671) or SF (p = 0.995). There were significant (p < 0.05) increases in npCSA compared to BL and CON in TRA at PT, DT1, and DT2, despite significant (p < 0.05) decreases in npCSA compared to PT at DT1 and DT2. There were significant (p < 0.05) increases in LF, Pθ and KE MVC at PT but only LF and torque at DT1. There were no significant (p > 0.05) changes in SF, specific force or TNFα at any time points. There was a significant correlation (p = 0.022, r = 0.57) between the relative changes in TNFα and npCSA at DT2 compared to PT. DISCUSSION: Neither RT nor a period of short term detraining altered the quality of muscle (i.e., specific force) despite changes in morphology and function. TNFα does not appear to have any impact on RT-induced gains in muscle size or function, however, TNFα may play a role in inflammatory-status mediated muscle mass loss during subsequent detraining in healthy adults.

Whole-body and segmental analysis of body composition in adult males with achondroplasia using dual X-ray absorptiometry.

Achondroplasia is a condition characterized by a genetic mutation affecting long bone endplate development. Current data suggests that the bone mineral content (BMC) and bone mineral density (BMD) of achondroplasic populations are below age matched individuals of average stature (controls). Due to the disproportionate limb-to-torso length compared to controls however, the lower BMC and BMD may be nullified when appropriately presented. The aim of this study was to measure whole-body and segmental body composition in adult males with achondroplasia (N = 10, 22 ±3 yrs), present data relative to whole-body and whole-limb values and compare all values to age matched controls (N = 17, 22 ±2 yrs). Dual X-ray absorptiometry (DEXA) was used to measure the in vivo mass of the whole-body and 15 segments, from which BMD, BMC, fat free mass (FFM) and body fat mass were measured. BMC of lumbar vertebrae (L1-4) was also measured and presented as a volumetric BMD (BMDVOL). The achondroplasic group had less BMC, BMD and FFM, and more body fat mass than controls as a whole-body measure. The lower achondroplasic BMC and BMD was somewhat nullified when presented relative to whole-body and whole-limb values respectively. There was no difference in lumbar BMDVOL between groups. Whole-body BMD measures presented the achondroplasic group as 'osteopenic'. When relative to whole-limb measures however, achondroplasic BMD descriptions were normal. Further work is needed to create a body composition database for achondroplasic population's, or for clinicians to present achondroplasic body composition values relative to the whole-limb.

Effect of mouthguard design on retention and potential issues arising with usability in sport.

BACKGROUND/AIMS: Mouthguard retention could potentially increase an athlete's motivation to wear the device, due to potential improvements in physical comfort. The aim of this study was to examine the retentive properties of selected customised mouthguard designs, during normal conditions (dry) and within the presence of artificial saliva (wet). Additionally, the correlation between thickness and retention was investigated. MATERIAL AND METHODS: Six different custom mouthguard designs (MG1-MG6) reported in previous studies, were pressure-formed with 2 and 4 mm blanks accordingly. Thickness was measured 10 times at seven anatomical points and the mean (±SD) was recorded. A novel rig was fabricated to connect the mouthguards to a Hounsfield H10KS Tensometer, which was used to fully displace each device from the model at a constant rate of 50 mm/min. The test was repeated under both dry and wet conditions. RESULTS: Retention forces recorded at the anterior region demonstrated higher measurements under wet conditions than dry (P < 0.001). The total retention of the mouthguards was influenced by alterations in their design. Trend analysis indicated that 64% of MG retention could be explained by their thickness under dry conditions and 55% when wet. CONCLUSIONS: Design and thickness of mouthguards are key factors in retention. Mouthguard fabrication techniques should be considered in order to minimize dislodgment of the devices as well as potentially increasing the wearability of mouthguards during sport.

Morphological and Mechanical Properties of the Human Patella Tendon in Adult Males With Achondroplasia.

Achondroplasia is a genetic mutation of fibroblast growth factor receptor resulting in impaired growth plate development in long bones due to lower collagen turnover. Despite the characteristic shorter stature and lower strength in Achondroplasic groups, little is known of the tendon mechanical properties under loading. The aim of this study was therefore to conduct a between measure design of patella tendon (PT) mechanical properties (stress, strain, stiffness and Young's Modulus) in 10 men with Achondroplasia (22 ± 3 years) and 17 male controls (22 ± 2 years). PT mechanical properties were measured during isometric maximal voluntary contraction (iMVC) of the knee extensors using ultrasonography. The Achondroplasic group produced 54% less stress at iMVC than controls (29.4 ± 8.0 v 64.5 ± 14.0 MPa, P < 0.001, d = 3.12). Maximal excursion of the Achondroplasic PT was 22% less than controls at iMVC (7.4 ± 2.1 v 5.5 ± 1.7 mm, P < 0.001, d = 0.99), but there was no difference in strain between groups (13 ± 4 v 13 ± 3%, P > 0.05). Achondroplasic PT were 47% less stiff (748 ± 93 v 1418 ± 101 N·mm-1, P < 0.001, d = 6.89) and had a 51% lower Young's modulus (0.39 ± 0.09 v 0.77 ± 0.14 GPa, P < 0.001, d = 3.46) than controls at iMVC. Achondroplasic PT are indeed more compliant than controls which may contribute to lower relative force production. The causes of higher Achondroplasic PT compliance are unclear but are likely due to the collagen related genetic mutation which causes Achondroplasia.

The Oxygen Consumption and Metabolic Cost of Walking and Running in Adults With Achondroplasia.

The disproportionate body mass and leg length of Achondroplasic individuals may affect their net oxygen consumption ([Formula: see text]O2) and metabolic cost (C) when walking at running compared to those of average stature (controls). The aim of this study was to measure submaximal [Formula: see text]O2 and C during a range of set walking speeds (SWS; 0.56 - 1.94 m⋅s-1, increment 0.28 m⋅s-1), set running speeds (SRS; 1.67 - 3.33 m⋅s-1, increment 0.28 m⋅s-1) and a self-selected walking speed (SSW). [Formula: see text]O2 and C was scaled to total body mass (TBM) and fat free mass (FFM) while gait speed was scaled to leg length using Froude's number (Fr). Achondroplasic [Formula: see text]O2TBM and [Formula: see text]O2FFM were on average 29 and 35% greater during SWS (P < 0.05) and 12 and 18% higher during SRS (P < 0.05) than controls, respectively. Achondroplasic CTBM and CFFM were 29 and 33% greater during SWS (P < 0.05) and 12 and 18% greater during SRS (P < 0.05) than controls, respectively. There was no difference in SSW [Formula: see text]O2TBM or [Formula: see text]O2FFM between groups (P > 0.05), but CTBM and CFFM at SSW were 23 and 29% higher (P < 0.05) in the Achondroplasic group compared to controls, respectively. [Formula: see text]O2TBM and [Formula: see text]O2FFM correlated with Fr for both groups (r = 0.984 - 0.999, P < 0.05). Leg length accounted for the majority of the higher [Formula: see text]O2TBM and [Formula: see text]O2FFM in the Achondroplasic group, but further work is required to explain the higher Achondroplasic CTBM and CFFM at all speeds compared to controls. New and Noteworthy: There is a leftward shift of oxygen consumption scaled to total body mass and fat free mass in Achondroplasic adults when walking and running. This is nullified when talking into account leg length. However, despite these scalars, Achondroplasic individuals have a higher walking and metabolic cost compared to age matched non-Achondroplasic individuals, suggesting biomechanical differences between the groups.

Gender associated muscle-tendon adaptations to resistance training.

PURPOSE: To compare the relative changes in muscle-tendon complex (MTC) properties following high load resistance training (RT) in young males and females, and determine any link with circulating TGFß-1 and IGF-I levels. METHODS: Twenty-eight participants were assigned to a training group and subdivided by sex (T males [TM] aged 20±1 year, n = 8, T females [TF] aged 19±3 year, n = 8), whilst age-matched 6 males and 6 females were assigned to control groups (ConM/F). The training groups completed 8 weeks of resistance training (RT). MTC properties (Vastus Lateralis, VL) physiological cross-sectional area (pCSA), quadriceps torque, patella tendon stiffness [K], Young's modulus, volume, cross-sectional area, and length, circulating levels of TGFß-1 and IGF-I were assessed at baseline and post RT. RESULTS: Post RT, there was a significant increase in the mechanical and morphological properties of the MTC in both training groups, compared to ConM/F (p<0.001). However, there were no significant sex-specific changes in most MTC variables. There were however significant sex differences in changes in K, with females exhibiting greater changes than males at lower MVC (Maximal Voluntary Contraction) force levels (10% p = 0.030 & 20% MVC p = 0.032) and the opposite effect seen at higher force levels (90% p = 0.040 & 100% MVC p = 0.044). There were significant increases (p<0.05) in IGF-I in both TF and TM following training, with no change in TGFß-1. There were no gender differences (p>0.05) in IGF-I or TGFß-1. Interestingly, pooled population data showed that TGFß-1 correlated with K at baseline, with no correlations identified between IGF-I and MTC properties. CONCLUSIONS: Greater resting TGFß-1 levels are associated with superior tendon mechanical properties. RT can impact opposite ends of the patella tendon force-elongation relationship in each sex. Thus, different loading patterns may be needed to maximize resistance training adaptations in each sex.

Specific force of the vastus lateralis in adults with achondroplasia.

Achondroplasia is a clinical condition defined by shorter stature and disproportionate limb length. Force production in able-bodied individuals (controls) is proportional to muscle size, but given the disproportionate nature of achondroplasia, normalizing to anatomical cross-sectional area (ACSA) is inappropriate. The aim of this study was to assess specific force of the vastus lateralis (VL) in 10 adults with achondroplasia (22 ± 3 yr) and 18 sex-matched controls (22 ± 2 yr). Isometric torque (iMVCτ) of the dominant knee extensors (KE) and in vivo measures of VL muscle architecture, volume, activation, and patella tendon moment arm were used to calculate VL physiological CSA (PCSA), fascicle force, and specific force in both groups. Achondroplasic muscle volume was 53% smaller than controls (284 ± 36 vs. 604 ± 102 cm3, P < 0.001). KE iMVCτ was 63% lower in achondroplasia compared with controls (95 ± 24 vs. 256 ± 47 N⋅m, P < 0.001). Activation and moment arm length were similar between groups ( P > 0.05), but coactivation of bicep femoris of achondroplasic subjects was 70% more than controls (43 ± 20 vs. 13 ± 5%, P < 0.001). Achondroplasic subjects had 58% less PCSA (43 ± 10 vs. 74.7 ± 14 cm2, P < 0.001), 29% lower fascicle force (702 ± 235 vs. 1704 ± 303 N, P < 0.001), and 29% lower specific force than control subjects (17 ± 6 vs. 24 ± 6 N⋅cm-2, P = 0.012). The smaller VL specific force in achondroplasia may be attributed to infiltration of fat and connective tissue, rather than to any difference in myofilament function. NEW & NOTEWORTHY The novel observation of this study was the measurement of normalized force production in a group of individuals with disproportionate limb length-to-torso ratios.

The effect of time constraints and running phases on combined event pistol shooting performance.

The combined event is a crucial aspect of the modern pentathlon competition, but little is known about how shooting performance changes through the event. This study aimed to identify (i) how performance-related variables changed within each shooting series and (ii) how performance-related variables changed between each shooting series. Seventeen modern pentathletes completed combined event trials. An optoelectronic shooting system recorded score and pistol movement, and force platforms recorded centre of pressure movement 1 s prior to every shot. Heart rate and blood lactate values were recorded throughout the event. Whilst heart rate and blood lactate significantly increased between series (P < 0.05), there were no accompanying changes in the time period that participants spent aiming at the target, shot score, pistol movement or centre of pressure movement (P > 0.05). Thus, combined event shooting performance following each running phase appears similar to shooting performance following only 20 m of running. This finding has potential implications for the way in which modern pentathletes train for combined event shooting, and highlights the need for modern pentathletes to establish new methods with which to enhance shooting accuracy.

The effect of manipulating root mean square window length and overlap on reliability, inter-individual variability, statistical significance and clinical relevance of electromyograms.

Numerous ways exist to process raw electromyograms (EMGs). However, the effect of altering processing methods on peak and mean EMG has seldom been investigated. The aim of this study was to investigate the effect of using different root mean square (RMS) window lengths and overlaps on the amplitude, reliability and inter-individual variability of gluteus maximus EMGs recorded during the clam exercise, and on the statistical significance and clinical relevance of amplitude differences between two exercise conditions. Mean and peak RMS of 10 repetitions from 17 participants were obtained using processing window lengths of 0.01, 0.15, 0.2, 0.25 and 1 s, with no overlap and overlaps of 25, 50 and 75% of window length. The effect of manipulating window length on reliability and inter-individual variability was greater for peak EMG (coefficient of variation [CV] <9%) than for mean EMG (CV <3%), with the 1 s window generally displaying the lowest variability. As a consequence, neither statistical significance nor clinical relevance (effect size [ES]) of mean EMG was affected by manipulation of window length. Statistical significance of peak EMG was more sensitive to changes in window length, with lower p-values generally being recorded for the 1 s window. As use of different window lengths has a greater effect on variability and statistical significance of the peak EMG, then clinicians should use the mean EMG. They should also be aware that use of different numbers of exercise repetitions and participants can have a greater effect on EMG parameters than length of processing window.

Muscular adaptations and insulin-like growth factor-1 responses to resistance training are stretch-mediated.

INTRODUCTION: Modulation of muscle characteristics was attempted through altering muscle stretch during resistance training. We hypothesized that stretch would enhance muscle responses. METHODS: Participants trained for 8 weeks, loading the quadriceps in a shortened (SL, 0-50° knee flexion; n=10) or lengthened (LL, 40-90°; n=11) position, followed by 4 weeks of detraining. Controls (CON; n=10) were untrained. Quadriceps strength, vastus lateralis architecture, anatomical cross-sectional area (aCSA), and serum insulin-like growth factor-1 (IGF-1) were measured at weeks 0, 8, 10, and 12. RESULTS: Increases in fascicle length (29±4% vs. 14±4%), distal aCSA (53±12% vs. 18±8%), strength (26±6% vs. 7±3%), and IGF-1 (31±6% vs. 7±6%) were greater in LL compared with SL muscles (P<0.05). No changes occurred in CON. Detraining decrements in strength and aCSA were greater in SL than LL muscles (P<0.05). CONCLUSIONS: Enhanced muscle in vivo (and somewhat IGF-1) adaptations to resistance training are concurrent with muscle stretch, which warrants its inclusion within training.

Impact of range of motion during ecologically valid resistance training protocols on muscle size, subcutaneous fat, and strength.

The impact of using different resistance training (RT) kinematics, which therefore alters RT mechanics, and their subsequent effect on adaptations remain largely unreported. The aim of this study was to identify the differences to training at a longer (LR) compared with a shorter (SR) range of motion (ROM) and the time course of any changes during detraining. Recreationally active participants in LR (aged 19 ± 2.6 years; n = 8) and SR (aged 19 ± 3.4 years; n = 8) groups undertook 8 weeks of RT and 4 weeks of detraining. Muscle size, architecture, subcutaneous fat, and strength were measured at weeks 0, 8, 10, and 12 (repeated measures). A control group (aged 23 ± 2.4 years; n = 10) was also monitored during this period. Significant (p > 0.05) posttraining differences existed in strength (on average 4 ± 2 vs. 18 ± 2%), distal anatomical cross-sectional area (59 ± 15 vs. 16 ± 10%), fascicle length (23 ± 5 vs. 10 ± 2%), and subcutaneous fat (22 ± 8 vs. 5 ± 2%), with LR exhibiting greater adaptations than SR. Detraining resulted in significant (p > 0.05) deteriorations in all muscle parameters measured in both groups, with the SR group experiencing a more rapid relative loss of postexercise increases in strength than that experienced by the LR group (p > 0.05). Greater morphological and architectural RT adaptations in the LR (owing to higher mechanical stress) result in a more significant increase in strength compared with that of the SR. The practical implications for this body of work follow that LR should be observed in RT where increased muscle strength and size are the objective, because we demonstrate here that ROM should not be compromised for greater external loading.

The manipulation of strain, when stress is controlled, modulates in vivo tendon mechanical properties but not systemic TGF-ß1 levels.

Modulators of loading-induced in vivo adaptations in muscle-tendon complex (MTC) mechanical properties remain unclear. Similarly contentious, is whether changes in MTC characteristics are associated with growth factor levels. Four groups were subjected to varying magnitudes of stress/strain: Group 1 trained with the MTC at a shortened position (MTCS; n = 10); Group 2 at a lengthened position (MTCL; n = 11; stress levels matched to MTCS); Group 3 over a wide range of motion (MTCX; n = 11); and Group 4 (n = 10) was the control population (no training). Patella tendon Stiffness (P < 0.001), Young's modulus, and quadriceps torque (P < 0.05) increments (only seen in the training groups), showed MTCL and MTCX groups responses to be superior to those of MTCS (P < 0.05). In addition, MTCL and MTCX better maintained adaptations compared to MTCS (P < 0.05) following detraining, with a pattern of slower loss of improvements at the early phase of detraining in all training groups. There were no significant changes (P > 0.05) in antagonist cocontraction, patella tendon dimensions or circulating transforming growth factor beta (TGF-ß1) levels following training or detraining in any of the groups. We conclude that chronically loading the MTC in a relatively lengthened position (which involves greater strains) enhances its mechanical properties, more so than loading in a shortened position. This is true even after normalizing for internal stress. The underlying endocrine mechanisms do not appear to be mediated via TGF-ß1, at least not at the systemic level. Our findings have implications with regard to the effectiveness of eccentric loading on improved tendon structural and mechanical properties.

Biomechanical analysis of the change in pistol shooting format in modern pentathlon.

Despite the importance of the Combined Event to the modern pentathlon competition, little is known about performance in the event. This study aimed to (i) identify the key variables affecting Combined Event shooting performance, and the extent to which these corresponded with those identified for precision shooting and (ii) investigate the impact of changing shooting format, and whether more successful precision shooters were also more successful in the Combined Event. Seven modern pentathletes and three pistol shooters completed precision and Combined Event trials. An opto-electronic shooting system recorded score and pistol movements, whilst force platforms recorded centre of pressure movements 1 s prior to every shot. Intra-individual analysis revealed that the extent of associations between variables was participant-specific, highlighting the need for individual analysis of performance. No participants displayed matching associations between variables for precision and Combined Event shooting, emphasising the difference between performances in the two events. Both groups experienced significantly reduced scores, and increased pistol and body movements for Combined Event shooting (P < 0.05). Despite the pistol shooters' greater precision shooting ability, no significant differences were evident between the groups' Combined Event performances (P > 0.05). This implies that experience in one event does not guarantee success in the other, indicating the importance of event specific training.

The influence of varying hip angle and pelvis position on muscle recruitment patterns of the hip abductor muscles during the clam exercise.

STUDY DESIGN: Within-subject, repeated-measures design. OBJECTIVES: To determine the influence of pelvis position and hip angle on activation of the hip abductors while performing the clam exercise. BACKGROUND: Therapeutic exercises are regularly employed to strengthen the hip abductors to improve lower-limb and pelvis stability. While previous studies primarily have compared the activity of hip abductor muscles between various exercises, few studies have examined the influence of varying the techniques of particular exercises on the relative activation of hip abductor muscles. Such information could be used to facilitate appropriate exercise instruction. METHODS: Muscle activation in 17 healthy, asymptomatic volunteers during 6 variations of the clam exercise was analyzed with surface electromyography. Electromyographic signals were recorded from the gluteus maximus, gluteus medius, and tensor fasciae latae. Normalized data were examined using 2-way, repeated-measures analyses of variance. RESULTS: The magnitude of gluteus maximus and gluteus medius activation was significantly greater when the pelvis was in neutral rather than reclined. Furthermore, gluteus medius activation was greatest when the hip was flexed to 60°. Activation of the tensor fasciae latae was not influenced by pelvis position or hip angle. CONCLUSION: A neutral pelvis position is advocated to optimize recruitment of the gluteus maximus and gluteus medius during the clam exercise. Increasing the hip flexion angle increases activation of the gluteus medius. Tensor fasciae latae activity was relatively low and generally unaffected by variations of the clam exercise.

Abdominal and hip flexor muscle activity during 2 minutes of sit-ups and curl-ups.

Previous studies have compared muscle activity between different types of sit-ups and curl-ups. However, few have examined the exercises used by the armed forces or investigated the influence of exercise duration on muscle activation. The aim of this study was to compare abdominal and hip flexor muscle activity between the style of sit-up used by the British Army and 4 variations of a curl-up, at the start, middle, and end of a 2-minute exercise period. Surface electromyograms (EMGs) were recorded from the upper and lower rectus abdominis, external oblique, transversus abdominis and internal oblique, and the rectus femoris (RF) of 23 British Army personnel. Isometric maximal voluntary contractions were used to normalize integrated EMGs to allow them to be compared between exercises. Curl-ups with arms crossed and feet restrained produced the highest integrated EMG in all the abdominal muscles (p < 0.05). Feet-restrained sit-ups and curl-ups also resulted in significantly higher activity in the RF than in nonrestrained versions of the curl-up (p < 0.001). The significant increase observed in muscle activity between the start and the end of the exercises (p < 0.001) was deemed to be in response to a reduction in force producing capacity of existing motor units. The RF experienced the greatest increase during exercises that activated the muscle the most, that is, sit-ups and curl-ups with feet restrained (p < 0.001). Previous research has indicated that such exercises produce high shear and compressive forces in the lower back, which can be injurious. Thus, if an organization wishes to assess the endurance of abdominal muscles, rather than hip flexors, then curl-ups without restraint of the feet should be performed instead of exercises in which the feet are restrained.

Diurnal variation in stature: do those with chronic low-back pain differ from asymptomatic controls?

BACKGROUND: Stature loss is a commonly used measure of spinal load. The aim of this study was to investigate the pattern of diurnal stature change in those with and without chronic low-back pain, over a 24-h period. METHODS: Eight participants with chronic low-back pain (age 24.6 (SD 4.3) years, height 1.76 (SD 0.08) m, body mass 72.8 (SD 11.1) kg) and eight controls (age 21.8 (SD 2.0) years, height 1.75 (SD 0.10) m, body mass 71.8 (SD 11.6) kg) participated in this investigation. Twenty-four stature measurements were performed over a 24-h period. FINDINGS: The trough to peak variation in stature of 17.9 mm (low-back pain group) and 17.6mm (control group) did not differ between groups (P>0.05). Both groups experienced greatest stature change in the 1st hour after rising (31.3% [low-back pain] and 44.6% [control] of total stature change). At approximately 18:00h the LBP group reached a plateau whilst the control group continued to lose stature. Between 14:00 and 18:00h both groups demonstrated a previously unreported recovery of stature. A significant correlation was found between low-back discomfort and stature change in the low-back pain group only. INTERPRETATION: No significant difference existed between groups in relation to total stature loss; however the low-back pain group appeared to reach their nadir earlier, possibly exposing other spinal structures to loading for a greater duration. This is supported by the relationship found between stature loss and discomfort. The reversal in stature loss in the afternoon may be of clinical significance and warrants further investigation.

How should we normalize electromyograms obtained from healthy participants? What we have learned from over 25 years of research.

Electromyograms (EMGs) need to be normalized if comparisons are sought between trials when electrodes are reapplied, as well as between different muscles and individuals. The methods used to normalize EMGs recorded from healthy individuals have been appraised for more than a quarter of a century. Eight methods were identified and reviewed based on criteria relating to their ability to facilitate the comparison of EMGs. Such criteria included the magnitude and pattern of the normalized EMG, reliability, and inter-individual variability. If the aim is to reduce inter-individual variability, then the peak or mean EMG from the task under investigation should be used as the normalization reference value. However, the ability of such normalization methods to facilitate comparisons of EMGs is questionable. EMGs from MVCs can be as reliable as those from submaximal contractions, and do not appear to be affected by contraction mode or joint kinematics, particularly for the elbow flexors. Thus, the EMG from an isometric MVC is endorsed as a normalization reference value. Alternatively the EMG from a dynamic MVC can be used, although it is recognized that neither method is guaranteed to be able to reveal how active a muscle is in relation to its maximal activation capacity.