Katherine Burgess

Plyometric vs. isometric training influences on tendon properties and muscle output.

The purpose of this study was to concurrently determine the effect that plyometric and isometric training has on tendon stiffness (K) and muscle output characteristics to compare any subsequent changes. Thirteen men trained the lower limbs either plyometrically or isometrically 2–3 times a week for a 6-week period. Medial gastrocnemius tendon stiffness was measured in vivo using ultrasonography during ramped isometric contractions before and after training. Mechanical output variables were measured using a force plate during concentric and isometric efforts. Significant (p < 0.05) training-induced increases in tendon K were seen for the plyometric (29.4%; 49.0 < 10.8 to 63.4 < 9.2 N·mm-1) and isometric groups (61.6%; 43.9 < 2.5 to 71.0 < 7.4 N·mm-1). Statistically similar increases in rate of force development and jump height were also seen for both training groups, with increases of 18.9 and 58.6% for the plyometric group and 16.7 and 64.3% for the isometric group, respectively. Jump height was found to be significantly correlated with tendon stiffness, such that stiffness could explain 21% of the variance in jump height. Plyometric training has been shown to place large stresses on the body, which can lead to a potential for injury, whereas explosive isometric training has been shown here to provide similar benefits to that of plyometric training with respect to the measured variables, but with reduced impact forces, and would therefore provide a useful adjunct for athletic training programs within a 6-week time frame.

Effect of Acute Tensile Loading on Gender-Specific Tendon Structural and Mechanical Properties

Stretching is commonly used prior to exercise, as it is thought to reduce the risk of injury, and it is also used in the preconditioning of tendon grafts. As tendon properties have been shown to be different between genders, it is proposed that stretching will differentially affect the structure. Here we examine the effect of acute stretch on the mechanical properties of both male and female medial gastrocnemius tendon. Female [20 years ± 1 (SEM), n = 17] and male (22 years ± 1, n = 18) subjects underwent a 5‐min passive dorsiflexion stretch. Prior to and post stretch medial gastrocnemius tendon stiffness (K), length (l) and cross‐sectional area (csa) were measured using ultrasonography and dynamometry. Stiffness and Youngs modulus (ε) were significantly reduced with stretch for both genders (p < 0.05). Females showed significantly (p < 0.05) greater pre‐ to poststretch decreases in K (22.4 vs. 8.8%) and ε (20.5 vs. 8.4%) in comparison to males. The present results show that stretching acutely reduces stiffness of the medial gastrocnemius tendon in females and males, with females showing significantly greater change. The observed disparity between genders may be due in part to variations in tendon moment arm and intrinsic differences in tendon composition. These differential changes in tendon mechanical properties have functional, motor control, and injury risk implications, as well as possible implications for preconditioning of tendon grafts.

Patellar tendon properties with fluctuating menstrual cycle hormones.

Burgess, KE, Pearson, SJ, and Onambélé, GL. Patellar tendon properties with fluctuating menstrual cycle hormones. J Strength Cond Res 24(8): 2088-2095, 2010-Debate continues over whether skeletal muscle performance and injury risk vary over the course of the menstrual cycle. Alterations in tendon properties may play a role in the potential fluctuations of both of these variables. The aim of the current study was to determine any association between menstrual cycle phase and corresponding levels of female sex hormones and tendon properties. Fifteen normally menstruating (28-32-day cycles) healthy females (age 23 ± 1 years, mass 63.1 ± 2.6 kg, height 1.66 ± 0.02 m) not taking any form of hormonal contraceptive took part in this study. In vivo patellar tendon properties and associated circulating hormonal levels were assessed on 3 occasions including days 3 ± 0.4, 13 ± 0.2, and 21 ± 0.3. Dynamometry, ultrasonography, electromyography, and biochemical assessment of circulating levels of estradiol and progesterone were utilized. No significant differences were seen in tendon mechanical properties among the 3 phases of the menstrual cycle (p > 0.05). Regressions were carried out and revealed that estrogen and maximal voluntary tendon force explained 17.8% (p = 0.043) of the variance in youngs modulus. Our findings link estrogen to a chronic, rather than an acute, impact on tendon behavior. These findings are relevant to clinical outcomes, exercise performance, and injury risk. In terms of tendon properties, menstrual cycle phase does not necessarily need to be considered when organizing training and competition schedules.

Tendon structural and mechanical properties do not differ between genders in a healthy community-dwelling elderly population

Elderly women are reportedly at higher risk of falling than their male counterparts. Postural balance is highly associated with fall risk and is also correlated with tendon structural and mechanical properties. Gender differences in tendon properties could partly explain the discrepancy in fall risk. Thus the purpose of this study was to investigate the possible gender difference in tendon properties in the elderly. The properties of the patellar tendon of 55 elderly (men n = 27, aged 72 ± 1 years, women n = 28, aged 70 ± 1 years) participants were tested. Tendon stiffness (K), length (L), and cross‐sectional area (CSA) were measured using B‐mode ultrasonography, dynamometry, and electromyography during ramped isometric knee extensions. There were no significant differences (p > 0.05) between men and women in tendon stiffness (elderly men 550.9 ± 29.2 vs. women 502.9 ± 44.9 Nmm−1) or in Youngs modulus (elderly men 0.32 ± 0.02 vs. women 0.36 ± 0.04 GPa). This elderly group had similar tendon structural and mechanical properties. The comparable characteristics in gender‐specific tendon properties in an elderly population exhibiting similar lifestyle characteristics to the current sample may not explain the reports in the literature regarding increased fall risk in elderly women relative to that seen in men of a similar age.

Menstrual cycle variations in oestradiol and progesterone have no impact on in vivo medial gastrocnemius tendon mechanical properties

BACKGROUND Tendon tissue contains oestrogen receptors and is therefore likely to be responsive to female sex hormones. Here we examine any effect of levels of female sex hormones associated with the menstrual cycle phase on corresponding tendon mechanical properties. METHODS Fifteen healthy females aged 23 (SEM 1.0 years) underwent three assessments of medial gastrocnemius tendon mechanical properties. Assessments were carried out once during days 1-4, 12-14 and 20-23 (with day 1 being the first day of menstruation). Venous blood samples were taken on the same days as tendon properties assessments to quantify serum levels of oestradiol and progesterone. FINDINGS There was no significant difference in the stiffness of the medial gastrocnemius tendon over the course of the menstrual cycle (days 1-4, 65.08 (SEM 5.16 Nm m(-1)), days 12-14, 62.73 (SEM 5.82 Nm m(-1)), days 20-23, 66.74 (SEM 7.14 Nm m(-1))). There were also no significant differences in tendon length and cross-sectional area which led to no significant differences in Youngs modulus values. No correlations were found between serum levels of oestradiol and/or progesterone and tendon stiffness and/or Youngs modulus. INTERPRETATION Acute fluctuations in female sex hormones have no significant effect on medial gastrocnemius tendon mechanical properties. In a context where studies are often limited to selecting only oral contraceptive-users as participants in order to minimise potential noise related to the anticipated effects of menstrual cycle hormones on physical performance, our findings provide the basis for enabling the pooling of female tendon data, regardless of the phase of the menstrual cycle of individual participant.

Serum relaxin levels affect the in vivo properties of some but not all tendons in normally menstruating young women

Relaxin (hRLX) is a hormone reported to affect collagen synthesis. Its effects are also thought to be modulated by other sex hormones, including oestrogen, which has previously been found to be associated with alterations of in vivo tendon properties. There is thus a potential for hRLX to impact on collagen, which could result in tendon structural and mechanical properties being modified. The present study therefore aimed to determine any interaction between hRLX and tendon stiffness, in normally menstruating women (n = 12). Tendon properties were determined using a combination of dynamometry and B‐mode ultrasound, whilst serum hRLX levels were established by ELISA. Serum hRLX level was seen to be negatively associated with patellar tendon stiffness (r =−0.56; P < 0.001), explaining 31% of the variance in this parameter. There was no association between hRLX and gastrocnemius tendon stiffness (P > 0.05), or with the cross‐sectional area of either of the two tendons (P > 0.05). In young, normally menstruating women, hRLX appears to have a significant effect on the patellar but not the gastrocnemius tendon stiffness. Where it has an effect, this appears to be on the intrinsic properties rather than on the dimensions of said tendon. Future work to elucidate the physiological cause of this selectivity in the impact of relaxin will be key to mapping the impact of the endocrine system on the phenotype of tendinous tissue.

The physiological effect of a 'climb assist' device on vertical ladder climbing.

Abstract ‘Climb assist’ claims to reduce strain when climbing ladders; however, no research has yet substantiated this. The purpose of this study was to assess the physiological and psychophysical effects of climb assist on 30 m ladder climbing at a minimum acceptable speed. Eight participants (six male and two female) climbed a 30 m ladder at 24 rungs per minute with and without climb assist, and were monitored for heart rate (HR), O2 and rate of perceived exertion (RPE). All three variables decreased significantly (p < 0.05) with climb assist with O2 decreasing by 22.5%, HR by 14.8% and RPE decreasing by a mean of 2.3 units on the 10-point Borg scale. When descending the ladder O2 decreased by a mean of 42% compared to that ascending. At the minimal acceptable climbing speed climb assist decreases the physiological strain on climbers, as demonstrated by reduced O2, HR and perceived exertion. Practitioner Summary: ‘Climb assist’ systems claim to reduce strain when climbing, however; no research has yet been published to substantiate this. A crossover study compared O2, HR and RPE at a minimal acceptable climbing speed with and without climb assist. Climb assist significantly reduced all variables confirming it reduces strain when climbing.

The effect of pitched and vertical ladder ergometer climbing on cardiorespiratory and psychophysical variables

This study aimed to assess whether modifying the pitch of a 75° ladder ergometer to vertical had a cardiorespiratory or psychophysical effect on climbing. Nine male participants climbed a ladder ergometer at 75° and subsequently at 90°, adjusted for an equivalent vertical climb rate, completing three climbing bouts at different vertical speeds. One participant dropped out being unable to complete the climb under the 90° condition. Each was monitored for heart rate (HR), V˙O2 and rating of perceived exertion (RPE). Results showed vertical climbing induced higher V˙O2 (mean increase 17.3%), higher HR (mean increase 15.8%), and higher RPE at all speeds and that moving from 75°to vertical exacerbates the effect of speed on the cardiorespiratory response to climbing. This may be explained by increased force production required to maintain balance in a vertical climbing position when the bodys centre of mass is not above the feet.

Physiological responses to prolonged saturation diving: a field-based pilot study

This study aimed to assess the effect of extreme environmental exposure during an operational saturation dive on airway inflammation (exhaled nitric oxide (FeNo)), components of fitness (flexibility and aerobic capacity) and blood hematological variables. Six saturation divers, who undertook a 26±0.5 day operational saturation dive were recruited to take part in this study. Participants completed a field-based repeated measure test battery on three occasions (pre-dive, post-dive and 24 hours after saturation dive). Hemoglobin concentration was significantly (P⟨0.001) reduced from pre- (15.3±0.8 g/dL) to post-saturation (14.25±1.2 g/dL) dive but recovered toward baseline values within 24 hours (15.13±1.03 g/dL; P=0.04). Similarly, a reduction in plasma volume was observed in all participants from pre- to post-saturation dive trials. Airway inflammation response was non-significant, although a large inter-individual response was evident. Hip flexion, assessed by the sit and reach test did not change following the saturation dive. Data on aerobic capacity was collected in one participant only, due to practical difficulties in participant access. In summary, this is the first investigation to conduct a multiple-component field-based study on operational saturation divers. The findings for this exploratory study present interesting groundings for further investigation.

Can selenium supplementation modify oxidative stress in-vitro? A role for selenium supplementation in the prevention of cardiovascular disease

Background Two thirds of the UK population are either overweight or obese (body mass index (BMI) 25-29.9 and >30 kg/m respectively) and are typically characterised by systemic oxidative stress (OS); deemed to play a key role in cardiovascular disease (CVD) development. OS results from chronically high reactive oxidative species (ROS) formation and reduced antioxidant status. OS plays a key role in CVD development by initiating atherosclerosis (fatty plaque accumulation within the arterial walls); therefore obese individuals are at increased risk of atherosclerosis development. Increased monocyte ROS generation instigates atherosclerotic plaque formation by increasing the recruitment, binding and transmigration of monocytes across arterial endothelial cells and into the arterial wall. An increased dietary antioxidant intake or up-regulation of endogenous antioxidant enzymes may counteract this OS state and therefore lower CVD risk. Selenium is an essential dietary micronutrient incorporated within the catalytic site of endogenous antioxidant Glutathione Peroxidase (GPx) enzymes, which protect cells from OS and consequent cell damage. There is, however, a lack of knowledge concerning the effect of selenium supplementation in an OS state representative of sedentary overweight/obese individuals. The aim of this work was to investigate the ability of selenium supplementation to modify monocyte cell viability/ROS production under OS. Materials and methods U937 monocyte cells were supplemented with sodium selenite (Na2SeO3; 100nM or 200nM) or not and cultured for 48 hours at 37°C. Paraquat (100mM) and S-Nitroso-Nacetyl-DL-penicillamine (10mM) (PQ/SNAP) were added to the cells to induce OS. Cell viability was assessed via MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay while ROS production was determined by Flow Cytometry using the reagent CM-H2DC-FDA.