Ethinyl oestradiol administration in women suppresses synthesis of collagen in tendon in response to exercise

The influence of sex is a neglected focus in rotator cuff repair: A systematic review and meta-analysis

PURPOSE

Rotator cuff (RC) disorders are the most common cause of shoulder disability. The aim of this study was to quantify the evidence on the sex-related differences in RC repair.

METHODS

A systematic review of the literature was performed in January 2023 in PubMed, Wiley Cochrane Library and Web of Science on research articles on humans with RC tears treated surgically. A meta-analysis was performed to compare results in men and women. The Downs and Black score and the modified Coleman methodology score (MCMS) were used to assess the retrieved studies.

RESULTS

A total of 39,909 patients were enroled in the 401 studies analysed (45% women, 55% men). A trend toward more sex-balanced recruitment was observed over time. Only 4% of the studies on 1.5% of the documented patients presented disaggregated outcome data and were quantitatively analysed. A tendency for lower range of motion values after surgery was found for external shoulder rotation in women, with 39.9° ± 6.9° versus 45.3° ± 4.1° in men (p = 0.066). According to Downs and Black scores, four studies were good and 12 fair, with a main MCMS score of 69/100.

CONCLUSION

There is a lack of awareness on the importance to document women- and men-specific data. Only 4% of the articles disaggregated data, and it was possible to analyse only 1.5% of the literature population, a sample which cannot be considered representative of all patients. The lack of disaggregated data is alarming and calls for action to better study men and women differences to optimise the management of RC tears. This will be necessary to provide sex-specific information that could be of clinical relevance when managing RC repair.

LEVEL OF EVIDENCE

Level IV.

Effects of resistance exercise, collagen ingestion and circulating oestrogen concentration on collagen synthesis in a female athlete: A case report

We investigated the effects of resistance exercise (RE), hydrolysed collagen (HC) ingestion and circulating oestrogen concentration on collagen synthesis in a naturally menstruating female CrossFit athlete. In a double-blind, randomised cross-over design, the participant (36 years; height 1.61 m; mass 82.6 kg) consumed 0 or 30 g HC prior to performing back-squat RE when endogenous circulating oestrogen concentration was low (onset of menses, OM) and high (late follicular phase, LF) during two consecutive menstrual cycles. Ten 5-mL blood samples were collected during each of the four interventions to analyse concentrations of serum 17β-oestradiol, and biomarkers of type I collagen turnover, that is serum procollagen type I N-terminal propeptide (PINP, a biomarker of collagen synthesis) and plasma β-isomerised C-terminal telopeptide of type I collagen (β-CTX, a biomarker of collagen breakdown), as well as the serum concentration of 18 collagen amino acids. 17β-Oestradiol concentration was 5-fold higher at LF (891 ± 116 pmol L-1) than OM (180 ± 13 pmol L-1). The PINP concentration × time area under the curve (AUC) was higher in the 30 g HC OM intervention (201 μg L-1 h) than the 30 g HC LF (144 μg L-1 h), 0 g HC OM (151 μg L-1 h) and 0 g HC LF (122 μg L-1 h) interventions. β-CTX concentration decreased 1.4-fold from pre-RE to 6 h post-RE in all interventions. Thus, high circulating oestrogen concentration was associated with lower collagen synthesis following RE in this female athlete. Ingesting 30 g HC, however, augmented the collagen synthesis response at LF and particularly at OM. HIGHLIGHTS: What is the central question of this study? Does resistance exercise-induced collagen synthesis vary according to circulating oestrogen concentration in a naturally menstruating female athlete, and if so, does hydrolysed collagen ingestion have any impact? What is the main finding and its importance? Exercise-induced collagen synthesis was low when circulating oestrogen concentration was high and vice versa. However, ingesting 30 g hydrolysed collagen prior to exercise reduced the negative effect of oestrogen on collagen synthesis. As high circulating oestrogen has been associated with greater injury risk in females, supplementing exercise with hydrolysed collagen may help protect these tissues from injury.

Higher risk of Achilles tendon ruptures at competition than training sites in female collegiate gymnasts

BACKGROUND

Reportedly, 17.2% of collegiate female gymnasts experience Achilles tendon ruptures (ATRs). Cumulative microtraumas resulting in chronic tendinopathy/tendinitis may contribute to this high injury risk. We hypothesized that the risk of ATRs in female collegiate gymnasts increases with years of competitive gymnastics, that non-steroidal anti-inflammatory drug (NSAID) use is associated with less ATRs, and that the risk is larger during competition than training.

METHODS

Female gymnasts from 78 USA collegiate teams completed a survey assessing the prevalence of ATRs, NSAID use, age at which competitive gymnastics started and age at which ATR occurred, and whether ATRs occurred during training or competition.

RESULTS

Twenty-one of 103 gymnasts (20.4%, 95% CI: 13.6% to 29.4%) experienced ATRs. Eighteen of 21 ruptures (85.7%, 95% CI: 61.3% to 95.8%) occurred after more than ten years of competitive gymnastics (mean: 14.0±2.6 years, 95% CI: 12.8 to 15.2 years). ATRs occurred 0.08±0.01 (95% CI: 0.06 to 0.11) times per 1000 hours at training versus 1.85±0.11 (95% CI: 1.60 to 2.10) times per 1000 hours at competition (P<0.05). Prevalence of NSAID use was 27.6% (95% CI: 18.6% to 39.0%) in gymnasts without ATR but only 5.5% (95% CI: 0.6% to 35.5%, P=0.09) in gymnasts with ATR. Multiple regression analysis demonstrated a negative association between NSAID use and incidence of ATRs (P<0.05).

CONCLUSIONS

Female collegiate gymnasts are at high risk for ATRs, especially after more than ten years of competitive gymnastics and during competition.

Oral Contraception Use and Musculotendinous Injury in Young Female Patients: A Database Study

PURPOSE

The purpose of this study is to characterize the effect of sex and the influence of oral contraception usage on musculotendinous injury (MTI). Current literature suggests a disparity in the incidence of MTI between males and females. This may be attributed to inherent biological differences between the sexes, such as in the sex hormonal milieu. There is a lack of information associating sex hormone milieu and MTI.

METHODS

We searched the PearlDiver database (a for-fee healthcare database) for males, females taking oral contraceptives (OC), and eumenorrheic females not taking any form of hormonal contraceptives (non-OC) 18-39 yr old. The three populations were matched by age and body mass index. We queried the database for lower-extremity skeletal MTI diagnoses in these groups.

RESULTS

Each group contained 42,267 patients with orthopedic injuries. There were a total of 1476 (3.49%) skeletal MTI in the male group, 1078 (2.55%) in non-OC females, and 231 (0.55%) in OC females. Both the non-OC and the OC groups had a significantly smaller proportion of MTI than males ( P < 0.0001), and therefore these groups were less likely (adjusted odds ratios, 0.72 and 0.15, respectively) to experience MTI when controlled for potential covariates.

CONCLUSIONS

In this study, we show that females are less likely to develop MTI to total injuries, when compared with males, with OC using females being least likely followed by non-OC females. These results are consistent with other epidemiological studies; however, overall results in the literature are variable. This study adds to the emerging body of literature on sex hormone-influenced musculoskeletal injury but, more specifically, MTI, which have not been rigorously investigated.

Anabolic Resistance in the Pathogenesis of Sarcopenia in the Elderly: Role of Nutrition and Exercise in Young and Old People

The development of sarcopenia in the elderly is associated with many potential factors and/or processes that impair the renovation and maintenance of skeletal muscle mass and strength as ageing progresses. Among them, a defect by skeletal muscle to respond to anabolic stimuli is to be considered. Common anabolic stimuli/signals in skeletal muscle are hormones (insulin, growth hormones, IGF-1, androgens, and β-agonists such epinephrine), substrates (amino acids such as protein precursors on top, but also glucose and fat, as source of energy), metabolites (such as β-agonists and HMB), various biochemical/intracellular mediators), physical exercise, neurogenic and immune-modulating factors, etc. Each of them may exhibit a reduced effect upon skeletal muscle in ageing. In this article, we overview the role of anabolic signals on muscle metabolism, as well as currently available evidence of resistance, at the skeletal muscle level, to anabolic factors, from both in vitro and in vivo studies. Some indications on how to augment the effects of anabolic signals on skeletal muscle are provided.

Impact of essential amino acid intake, resistance exercise, and aging on the concentration of Achilles peritendinous amino acids and procollagen Iα1 in humans

Recent studies have shown that consuming amino acid-rich compounds improves tendon collagen content and biomechanical properties. Yet, it is unclear if the consumption of amino acids alters local (peritendinous) amino acid concentrations. If aging or exercise influence local amino acid concentrations in conjunction with an amino acid bolus is also not known. We conducted two studies. In Study 1, young women (n = 7, 25 ± 2 years) completed two identical resistance training sessions with either essential amino acid (EAA) or placebo consumption. In Study 2, an EAA bolus identical to Study 1 was given to younger (n = 7; 27 ± 1 year) and older adults (n = 6; 68 ± 2 years). Microdialysis was used to determine Achilles peritendinous amino acid and pro-collagen Iα1 (a marker of collagen synthesis) concentrations. In Study 1, amino acid consumption increased peritendinous concentrations of all EAA except histidine (p < 0.05). In Study 2, the peritendinous concentration of EAAs except for methionine, histidine, and lysine (p > 0.05) increased with time (p < 0.05). Further, the concentrations of most measured amino acids were greater in older adults (p < 0.05). Pro-collagen Iα1 concentration (p > 0.05) was unaffected by exercise, EAA, or aging (p > 0.05). Our findings demonstrate the following: (1) when not combined with exercise, an oral EAA bolus leads to only modest increases in Achilles peritendinous amino acid concentrations; (2) when combined with resistance exercise, EAA consumption resulted in greater peritendinous amino acid concentrations compared to no exercise; (3) the basal concentrations of most amino acids were greater in older adults, and (4) neither the EAA bolus nor exercise altered peritendinous pro-collagen concentrations.

The Influence of Different Modes of Exercise on Healthy and Injured Tendons

Tendons are essential components of the musculoskeletal system that links the skeletal muscle to the skeleton. This dense connective tissue exhibits great plasticity. Therefore, research on the influence of types of exercise, including acute and long-term training, on the structural and mechanical properties of tendons in athletic and sedentary populations is of critical importance in the design of scientific-based exercise plans and effective tendinopathy treatment. Here, we review recent studies on the relationship between exercise and tendon health and tendinopathy repair to provide a general understanding of how exercise may reshape tendons.

Recovery from Achilles Tendon Repair: A Combination of Postsurgery Outcomes and Insufficient Remodeling of Muscle and Tendon

INTRODUCTION

Achilles tendon rupture (ATR) patients have persistent functional deficits in the triceps surae muscle-tendon unit (MTU). The complex remodeling of the MTU accompanying these deficits remains poorly understood. The purpose of the present study was to associate in vivo and in silico data to investigate the relations between changes in MTU properties and strength deficits in ATR patients.

METHODS

Eleven male subjects who had undergone surgical repair of complete unilateral ATR were examined 4.6 ± 2.0 (mean ± SD) yr after rupture. Gastrocnemius medialis (GM) tendon stiffness, morphology, and muscle architecture were determined using ultrasonography. The force-length relation of the plantar flexor muscles was assessed at five ankle joint angles. In addition, simulations (OpenSim) of the GM MTU force-length properties were performed with various iterations of MTU properties found between the unaffected and the affected side.

RESULTS

The affected side of the patients displayed a longer, larger, and stiffer GM tendon (13% ± 10%, 105% ± 28%, and 54% ± 24%, respectively) compared with the unaffected side. The GM muscle fascicles of the affected side were shorter (32% ± 12%) and with greater pennation angles (31% ± 26%). A mean deficit in plantarflexion moment of 31% ± 10% was measured. Simulations indicate that pairing an intact muscle with a longer tendon shifts the optimal angular range of peak force outside physiological angular ranges, whereas the shorter muscle fascicles and tendon stiffening seen in the affected side decrease this shift, albeit incompletely.

CONCLUSIONS

These results suggest that the substantial changes in MTU properties found in ATR patients may partly result from compensatory remodeling, although this process appears insufficient to fully restore muscle function.

The Impact of Genistein Supplementation on Tendon Functional Properties and Gene Expression in Estrogen-Deficient Rats

Tendinopathy risk increases with menopause. The phytoestrogen genistein prevents collagen loss during estrogen deficiency (ovariectomy [OVX]). The influence of genistein on tendon function and extracellular matrix (ECM) regulation is not well known. We determined the impact of genistein on tendon function and the expression of several genes important for the regulation of tendon ECM. Eight-week-old rats (n = 42) were divided into three groups: intact, OVX, or OVX-genistein (6 mg/kg/day) for 6 weeks. Tail fascicles were assessed with a Deben tensile stage. Achilles tendon mRNA expression was determined with digital droplet polymerase chain reaction. Compared to intact, fascicle stress tended to be lower in untreated OVX rats (P = .022). Furthermore, fascicle modulus and energy density were greater in genistein-treated rats (P < .05) compared to intact. Neither OVX nor genistein altered expression of Col1a1, Col3a1, Casp3, Casp8, Mmp1a, Mmp2, or Mmp9 (P > .05). Compared to intact, Tnmd and Esr1 expression were greater and Pcna and Timp1 expression were lower in OVX rats (P < .05). Genistein treatment returned Tnmd, Pcna, and Timp1 to levels of intact-vehicle (P < .05), but did not alter Scx or Esr1 (P > .05). Several β-catenin/Wnt signaling-related molecules were not altered by OVX or genistein (P > .05). Our findings demonstrate that genistein improves tendon function in estrogen-deficient rats. The effect of genistein in vivo was predominately on genes related to cell proliferation rather than collagen remodeling.

Beneficial and Deleterious Effects of Female Sex Hormones, Oral Contraceptives, and Phytoestrogens by Immunomodulation on the Liver

The liver is considered the laboratory of the human body because of its many metabolic processes. It accomplishes diverse activities as a mixed gland and is in continuous cross-talk with the endocrine system. Not only do hormones from the gastrointestinal tract that participate in digestion regulate the liver functions, but the sex hormones also exert a strong influence on this sexually dimorphic organ, via their receptors expressed in liver, in both health and disease. Besides, the liver modifies the actions of sex hormones through their metabolism and transport proteins. Given the anatomical position and physiological importance of liver, this organ is evidenced as an immune vigilante that mediates the systemic immune response, and, in turn, the immune system regulates the hepatic functions. Such feedback is performed by cytokines. Pro-inflammatory and anti-inflammatory cytokines are strongly involved in hepatic homeostasis and in pathological states; indeed, female sex hormones, oral contraceptives, and phytoestrogens have immunomodulatory effects in the liver and the whole organism. To analyze the complex and interesting beneficial or deleterious effects of these drugs by their immunomodulatory actions in the liver can provide the basis for either their pharmacological use in therapeutic treatments or to avoid their intake in some diseases.

Influence of Oral Contraceptive Use on Adaptations to Resistance Training

Introduction: The majority of young women use oral contraceptives (OCs). Use of OCs has been associated with lower myofibrillar protein and tendon collagen synthesis rates, but it is unknown whether OCs will limit the adaptive response of myotendinous tissue to resistance training.

Design and Methods: Fourteen healthy untrained young regular OC users (24 ± 1 years, fat% 32 ± 1, 35 ± 2 ml⋅min^-1⋅kg^-1) and 14 NOC users (non-OC, controls) (24 ± 1 years, fat% 32 ± 2, 34 ± 2 ml⋅min^-1⋅kg^-1) performed a 10-week supervised lower extremity progressive resistance training program. Before and after the intervention biopsies from the vastus lateralis muscle and the patellar tendon were obtained. Muscle (quadriceps) and tendon cross-sectional area (CSA) was determined by magnetic resonance imaging (MRI) scans, and muscle fiber CSA was determined by histochemistry. Maximal isometric knee extension strength was assessed by dynamometry while 1 repetition maximum (RM) was determined during knee extension.

Results: Training enhanced CSA in both muscle (p < 0.001) and tendon (p < 0.01). A trend toward a greater increase in muscle CSA was observed for OC (11%) compared to NOC (8%) (interaction p = 0.06). Analysis of mean muscle fiber type CSA showed a trend toward an increase in type II muscle fiber area in both groups (p = 0.11, interaction p = 0.98), whereas type I muscle fiber CSA increased in the OC group (n = 9, 3821 ± 197 to 4490 ± 313 mm², p < 0.05), but not in NOC (n = 7, 4020 ± 348 to 3777 ± 354 mm², p = 0.40) (interaction p < 0.05). Post hoc analyses indicated that the effect of OCs on muscle mass increase was induced by the OC-users (n = 7), who used OCs containing 30 μg ethinyl estradiol (EE), whereas the response in users taking OCs with 20 μg EE (n = 7) did not differ from NOC. Both the OC and NOC group experienced an increase in maximal knee strength (p < 0.001) and 1RM leg extension (p < 0.001) after the training period with no difference between groups.

Conclusion: Use of OCs during a 10-week supervised progressive resistance training program was associated with a trend toward a greater increase in muscle mass and a significantly greater increase in type I muscle fiber area compared to controls. Yet, use of OCs did not influence the overall increase in muscle strength related to training.

Effect of Estrogen on Musculoskeletal Performance and Injury Risk

Estrogen has a dramatic effect on musculoskeletal function. Beyond the known relationship between estrogen and bone, it directly affects the structure and function of other musculoskeletal tissues such as muscle, tendon, and ligament. In these other musculoskeletal tissues, estrogen improves muscle mass and strength, and increases the collagen content of connective tissues. However, unlike bone and muscle where estrogen improves function, in tendons and ligaments estrogen decreases stiffness, and this directly affects performance and injury rates. High estrogen levels can decrease power and performance and make women more prone for catastrophic ligament injury. The goal of the current work is to review the research that forms the basis of our understanding how estrogen affects muscle, tendon, and ligament and how hormonal manipulation can be used to optimize performance and promote female participation in an active lifestyle at any age.

Transcriptomic analysis of short-term 17α-ethynylestradiol exposure in two Californian sentinel fish species sardine (Sardinops sagax) and mackerel (Scomber japonicus)

Endocrine disrupting chemicals (EDCs) are substances which disrupt normal functioning of the endocrine system by interfering with hormone regulated physiological pathways. Aquatic environments provide the ultimate reservoir for many EDCs as they enter rivers and the ocean via effluent discharges and accumulate in sediments. One EDC widely dispersed in municipal wastewater effluent discharges is 17α-ethynylestradiol (EE2), which is one of the most widely prescribed medicines. EE2 is a bio-active estrogen employed in the majority of oral contraceptive pill formulations. As evidence of the health risks posed by EDCs mount, there is an urgent need to improve diagnostic tools for monitoring the effects of pollutants. As the cost of high throughput sequencing (HTS) diminishes, transcriptional profiling of an organism in response to EDC perturbation presents a cost-effective way of screening a wide range of endocrine responses. Coastal pelagic filter feeding fish species analyzed using HTS provide an excellent tool for EDC risk assessment in the marine environment. Unfortunately, there are limited genome sequence data and annotation for many of these species including Pacific sardine (Sardinops sagax) and chub mackerel (Scomber japonicus), which limits the utility of molecular tools such as HTS to interrogate the effects of endocrine disruption. In this study, we carried out RNA sequencing (RNAseq) of liver RNA harvested from wild sardine and mackerel exposed for 5 h under laboratory conditions to a concentration of 12.5 pM EE2 in the tank water. We developed an analytical framework for transcriptomic analyses of species with limited genomic information. EE2 exposure altered expression patterns of key genes involved in important metabolic and physiological processes. The systems approach presented here provides a powerful tool for obtaining a comprehensive picture of endocrine disruption in aquatic organisms.

The effect of estrogen on tendon and ligament metabolism and function

Tendons and ligaments are crucial structures inside the musculoskeletal system. Still many issues in the treatment of tendon diseases and injuries have yet not been resolved sufficiently. In particular, the role of estrogen-like compound (ELC) in tendon biology has received until now little attention in modern research, despite ELC being a well-studied and important factor in the physiology of other parts of the musculoskeletal system. In this review we attempt to summarize the available information on this topic and to determine many open questions in this field.

Recovery responses of testosterone, growth hormone, and IGF-1 after resistance exercise

The complexity and redundancy of the endocrine pathways during recovery related to anabolic function in the body belie an oversimplistic approach to its study. The purpose of this review is to examine the role of resistance exercise (RE) on the recovery responses of three major anabolic hormones, testosterone, growth hormone(s), and insulin-like growth factor 1. Each hormone has a complexity related to differential pathways of action as well as interactions with binding proteins and receptor interactions. Testosterone is the primary anabolic hormone, and its concentration changes during the recovery period depending on the upregulation or downregulation of the androgen receptor. Multiple tissues beyond skeletal muscle are targeted under hormonal control and play critical roles in metabolism and physiological function. Growth hormone (GH) demonstrates differential increases in recovery with RE based on the type of GH being assayed and workout being used. IGF-1 shows variable increases in recovery with RE and is intimately linked to a host of binding proteins that are essential to its integrative actions and mediating targeting effects. The RE stress is related to recruitment of muscle tissue with the glandular release of hormones as signals to target tissues to support homeostatic mechanisms for metabolism and tissue repair during the recovery process. Anabolic hormones play a crucial role in the body’s response to metabolism, repair, and adaptive capabilities especially in response to anabolic-type RE. Changes of these hormones following RE during recovery in the circulatory biocompartment of blood are reflective of the many mechanisms of action that are in play in the repair and recovery process.

Sex-based difference in Achilles peritendinous levels of matrix metalloproteinases and growth factors after acute resistance exercise

Several recent investigations have demonstrated that the ability of various tendons to alter structural and functional properties in response to exercise are muted in women compared with men. We hypothesize that this disparity between men and women may be due to a reduced tendon production of key mediators of tendon extracellular matrix (ECM) remodeling in response to mechanical loading, e.g., exercise. Using microdialysis before and after an acute bout of resistance exercise, we evaluated Achilles peritendinous levels of insulin-like growth factor-1 (IGF-1) and interleukin-6 (IL-6), which have both been shown to increase tendon collagen synthesis. Additionally, the matrix remodeling enzymes matrix metalloproteinase-2 (MMP-2), MMP-9, and tissue inhibitor of metalloproteinase-1 (TIMP-1) were also evaluated. IGF-1 levels were elevated ( P < 0.05) to a similar extent in men and women after 3 h of exercise but remained elevated at 4 h in only women. IL-6 levels were ~4-fold greater after exercise in both men and women ( P < 0.05). MMP-2 levels increased to a similar extent (~2-3-fold) in men and women ( P < 0.05). In contrast, MMP-9 increased with exercise but only in men ( P < 0.05). Last, TIMP-1 levels also increased ( P < 0.05) with exercise in men and women but the increase was more prolonged in women. In conclusion, we observed modest sex differences in tendon release of MMP-9, TIMP-1, and IGF-1 after acute resistance exercise. If such differences persist throughout a chronic exercise training, they may contribute to the reduced ability of women to adapt to exercise compared with men.

NEW & NOTEWORTHY In this investigation we utilized microdialysis of the peritendinous Achilles to evaluate potential differences between men and women in tendon production of key regulators of extracellular matrix remodeling. We demonstrate that a modest sex-specific difference exists in peritendinous levels of several key extracellular matrix modulators after an acute bout of resistance exercise.

Short Duration Small Sided Football and to a Lesser Extent Whole Body Vibration Exercise Induce Acute Changes in Markers of Bone Turnover

We aimed to study whether short-duration vibration exercise or football sessions of two different durations acutely changed plasma markers of bone turnover and muscle strain. Inactive premenopausal women (n = 56) were randomized to complete a single bout of short (FG15) or long duration (FG60) small sided football or low magnitude whole body vibration training (VIB). Procollagen type 1 amino-terminal propeptide (P1NP) was increased during exercise for FG15 (51.6 ± 23.0 to 56.5 ± 22.5 μg·L⁻¹, mean ± SD, P < 0.05) and FG60 (42.6 ± 11.8 to 50.2 ± 12.8 μg·L⁻¹, P < 0.05) but not for VIB (38.8 ± 15.1 to 36.6 ± 14.7 μg·L⁻¹, P > 0.05). An increase in osteocalcin was observed 48 h after exercise (P < 0.05), which did not differ between exercise groups. C-terminal telopeptide of type 1 collagen was not affected by exercise. Blood lactate concentration increased during exercise for FG15 (0.6 ± 0.2 to 3.4 ± 1.2 mM) and FG60 (0.6 ± 0.2 to 3.3 ± 2.0 mM), but not for VIB (0.6 ± 0.2 to 0.8 ± 0.4 mM) (P < 0.05). Plasma creatine kinase increased by 55 ± 63% and 137 ± 119% 48 h after FG15 and FG60 (P < 0.05), but not after VIB (26 ± 54%, NS). In contrast to the minor elevation in osteocalcin in response to a single session of vibration exercise, both short and longer durations of small sided football acutely increased plasma P1NP, osteocalcin, and creatine kinase. This may contribute to favorable effects of chronic training on musculoskeletal health.

Influence of Menstrual Cycle and Oral Contraceptive Phase on Spinal Excitability

BACKGROUND

Rates of musculoskeletal injury differ substantially between the genders, with females more likely to experience conditions such as anterior cruciate ligament (ACL) injuries than males in the same sports. Emerging evidence suggests a significant hormonal contribution. Most research has focused solely on how hormonal fluctuations affect connective tissue, but a direct link between hormonal shifts, ligamentous laxity, and ACL injury has not been borne out. There is also evidence to suggest that sex hormones can modulate the central nervous system, but how this affects neuromuscular control is not well understood.

OBJECTIVE

To determine whether changes in sex hormone concentrations would alter spinal excitability, measured across the menstrual and oral contraceptive pill cycle. We hypothesized that spinal excitability would fluctuate across the menstrual cycle (with increased excitability during the periovulatory phase due to peak estradiol concentration), but that there would be no fluctuation in oral contraceptive users.

DESIGN

This was a prospective cohort study.

SETTING

The study took place at a biomechanics laboratory at a rehabilitation hospital.

PARTICIPANTS

A total of 30 healthy women aged 18-35 who were similar in age, body composition, and exercise-training status were included. Fifteen of the women were eumenorrheic and nonusers of oral contraceptives (nonusers), and 15 of the women were taking oral contraceptives (users).

MAIN OUTCOME MEASURES

H-reflex (Hmax/Mmax ratio), serum estradiol, and progesterone concentrations were measured at 3 time points during the menstrual and contraceptive pill cycle.

RESULTS

The H-reflex (Hmax/Mmax ratio) remained stable across the menstrual and contraceptive pill cycle. Spinal excitability was lower in the users compared with the nonusers across all testing sessions, but this was not statistically significant.

CONCLUSIONS

Our results suggest that acute fluctuations of endogenous estradiol and progesterone do not modulate spinal excitability. However, long-term exposure to exogenous estrogen and progesterone (oral contraceptives) might have an impact on spinal excitability and neuromuscular control. Further research is necessary to better understand the potential differential effect of endogenous and exogenous sex hormones on spinal excitability.

Does menopausal hormone therapy (MHT), exercise or a combination of both, improve pain and function in post-menopausal women with greater trochanteric pain syndrome (GTPS)? A randomised controlled trial

BACKGROUND

Greater trochanteric pain syndrome (GTPS) is pathology in the gluteus medius and minimus tendons and trochanteric bursa that causes debilitating tendon pain and dysfunction, particularly in post-menopausal women. Limited evidence in clinical studies suggests hormone changes after menopause may have a negative effect on tendon. This protocol describes a randomised controlled trial comparing the effectiveness of menopausal hormone therapy (MHT) and exercise therapy in reducing pain and dysfunction associated with GTPS in post-menopausal women.

METHOD

One hundred and sixteen post-menopausal women will be recruited and randomised to receive one of two exercise programs (sham or targeted intervention exercise) and transdermal creams (MHT cream containing oestradiol 50mcg and norethisterone acetate 140mcg or placebo cream). Interventions will be 12-weeks in duration and outcomes will be examined at baseline, 12-weeks and 52-weeks. The primary outcome measure will be the VISA-G questionnaire and secondary outcomes measures will include three hip pain and function questionnaires (Hip dysfunction and Osteoarthritis Outcome Score, Oxford Hip Score, Lateral Hip Pain questionnaire), a global change in symptom questionnaire (using a 15-point Likert scale) and a quality of life measure (AQoL-8D questionnaire). Data will be analysed using the intention to treat principle.

DISCUSSION

This study is the first randomised controlled trial to compare the effectiveness of menopausal hormone therapy therapy alone, and with the combination of exercise therapy, to treat pain and dysfunction associated with GTPS. This study has been pragmatically designed to ensure that the interventions in this study can be integrated into policy and clinical practice if found to be effective in the treatment of GTPS in post-menopausal women. If successful, there is potential for this treatment regimen to be explored in future studies of other persistent tendon conditions in the post-menopausal population.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12614001157662 Registered 31 October 2014.

The effect of female sex hormone supplementation on tendon in pre and postmenopausal women: A systematic review

OBJECTIVES

Oestrogen deprivation has been shown to have a negative effect on connective tissue and its turnover. A link may exist between supplemental oestrogen, preservation of tendon collagen and less tendon abnormality. The aim was to determine the effects of female sex hormone supplementation (FSHS) on tendon.

METHODS

A systematic search of nine key health databases; Medline, CINAHL, EMBASE, SPORTDiscus, AUSPORT and AMI, Cochrane Library, SafetyLit and PEDro was completed (to Feb 24, 2016). The search yielded 6378 records using terms relating to hormone (oestrogen, estrogen, hormone replacement therapy, HRT, estrogen therapy, oestrogen therapy, oral contraceptive pill) and tendon. Quality assessment, data extraction and data synthesis of included papers was undertaken.

RESULTS

Low level of evidence for all outcomes; no positive or negative link between FSHS and molecular, mechanical and morphological tendon response outcomes, and the addition of exercise to FSHS, had minimal effects on tendon CSA.

CONCLUSIONS

The effect of oestrogen supplementation on tendon is contradictory and inconsistent. This review suggests there is a need for further studies to understand the effects of FSHS on tendon tissue at a mechanical, morphological and molecular level.

Sex Hormones and Tendon

The risk of overuse and traumatic tendon and ligament injuries differ between women and men. Part of this gender difference in injury risk is probably explained by sex hormonal differences which are specifically distinct during the sexual maturation in the teenage years and during young adulthood. The effects of the separate sex hormones are not fully elucidated. However, in women, the presence of estrogen in contrast to very low estrogen levels may be beneficial during regular loading of the tissue or during recovering after an injury, as estrogen can enhance tendon collagen synthesis rate. Yet, in active young female athletes, physiological high concentration of estrogen may enhance the risk of injuries due to reduced fibrillar crosslinking and enhanced joint laxity. In men, testosterone can enhance tendon stiffness due to an enhanced tendon collagen turnover and collagen content, but testosterone has also been linked to a reduced responsiveness to relaxin. The present chapter will focus on sex difference in tendon injury risk, tendon morphology and tendon collagen turnover, but also on the specific effects of estrogen and androgens.

Estrogen inhibits lysyl oxidase and decreases mechanical function in engineered ligaments

Women are more likely to suffer an anterior cruciate ligament (ACL) rupture than men, and the incidence of ACL rupture in women rises with increasing estrogen levels. We used an engineered ligament model to determine how an acute rise in estrogen decreases the mechanical properties of ligaments. Using fibroblasts isolated from human ACLs from male or female donors, we engineered ligaments and determined that ligaments made from female ACL cells had more collagen and were equal in strength to those made from male ACL cells. We then treated engineered ligaments for 14 days with low (5 pg/ml), medium (50 pg/ml), or high (500 pg/ml) estrogen, corresponding to the range of in vivo serum estrogen concentrations and found that collagen within the grafts increased without a commensurate increase in mechanical strength. Mimicking the menstrual cycle, with 12 days of low estrogen followed by 2 days of physiologically high estrogen, resulted in a decrease in engineered ligament mechanical function with no change in the amount of collagen in the graft. The decrease in mechanical stiffness corresponded with a 61.7 and 76.9% decrease in the activity of collagen cross-linker lysyl oxidase with 24 and 48 h of high estrogen, respectively. Similarly, grafts treated with the lysyl oxidase inhibitor β-aminoproprionitrile (BAPN) for 24 h showed a significant decrease in ligament mechanical strength [control (CON) = 1.58 ± 0.06 N; BAPN = 1.06 ± 0.13 N] and stiffness (CON = 7.7 ± 0.46 MPa; BAPN = 6.1 ± 0.71 MPa) without changing overall collagen levels (CON = 396 ± 11.5 μg; BAPN = 382 ± 11.6 μg). Together, these data suggest that the rise in estrogen during the follicular phase decreases lysyl oxidase activity in our engineered ligament model and if this occurs in vivo may decrease the stiffness of ligaments and contribute to the elevated rate of ACL rupture in women.

Prevalence of and risk factors for asymptomatic rotator cuff tears in postmenopausal women

OBJECTIVE

Rotator cuff tendon tears increase with age, but no study has specifically addressed prevalence changes in women from premenopause to postmenopause. The aims of this study were to evaluate the prevalence of rotator cuff asymptomatic tears in postmenopausal women and to study their relationship with anthropometric and metabolic measures.

METHODS

Premenopausal and postmenopausal women who were free from shoulder pain/functional impairment were enrolled. Body mass index (BMI), fasting glucose, triglycerides, total cholesterol, and high-density lipoprotein (HDL) cholesterol were evaluated. Both shoulders were examined by ultrasound imaging. For the purposes of this study, only full-thickness tears (classified as small, large, or massive) were taken into account.

RESULTS

The prevalence of full-thickness tears (mainly localized in the supraspinatus tendon of the dominant side) was significantly higher in the postmenopausal group (8.9% vs 3.1%), with small, medium, and large tears in 60%, 20%, and 20% of cases, respectively. In women with tears, intragroup comparison showed significantly higher values for BMI and fasting glucose, and lower levels of HDL cholesterol; no difference was found for triglycerides and total cholesterol in premenopausal and postmenopausal women, respectively. On multiple logistic regression analysis, the probability of detecting a tear in both groups was positively related to high values of BMI and lower levels of HDL cholesterol.

CONCLUSIONS

The prevalence of asymptomatic full-thickness tears is increased in the postmenopausal period, and there is an association between tears and metabolic disorders. Because asymptomatic tears have a great potential to evolve into symptomatic painful shoulder, a precocious discovery of this pathology may allow the planning of preventive and therapeutic measures.

Tendon protein synthesis rate in classic Ehlers-Danlos patients can be stimulated with insulin-like growth factor-I

The classic form of Ehlers-Danlos syndrome (cEDS) is an inherited connective tissue disorder, where mutations in type V collagen-encoding genes result in abnormal collagen fibrils. Thus the cEDS patients have pathological connective tissue morphology and low stiffness, but the rate of connective tissue protein turnover is unknown. We investigated whether cEDS affected the protein synthesis rate in skin and tendon, and whether this could be stimulated in tendon tissue with insulin-like growth factor-I (IGF-I). Five patients with cEDS and 10 healthy, matched controls (CTRL) were included. One patellar tendon of each participant was injected with 0.1 ml IGF-I (Increlex, Ipsen, 10 mg/ml) and the contralateral tendon with 0.1 ml isotonic saline as control. The injections were performed at both 24 and 6 h prior to tissue sampling. The fractional synthesis rate (FSR) of proteins in skin and tendon was measured with the stable isotope technique using a flood-primed continuous infusion over 6 h. After the infusion one skin biopsy and two tendon biopsies (one from each patellar tendon) were obtained. We found similar baseline FSR values in skin and tendon in the cEDS patients and controls [skin: 0.005 ± 0.002 (cEDS) and 0.007 ± 0.002 (CTRL); tendon: 0.008 ± 0.001 (cEDS) and 0.009 ± 0.002 (CTRL) %/h, mean ± SE]. IGF-I injections significantly increased FSR values in cEDS patients but not in controls (delta values: cEDS 0.007 ± 0.002, CTRL 0.001 ± 0.001%/h). In conclusion, baseline protein synthesis rates in connective tissue appeared normal in cEDS patients, and the patients responded with an increased tendon protein synthesis rate to IGF-I injections.

Healing of subcutaneous tendons: Influence of the mechanical environment at the suture line on the healing process

Tendon ruptures remain a significant musculoskeletal injury. Despite advances in surgical techniques and procedures, traditional repair techniques maintain a high incidence of rerupture or tendon elongation. Mechanical loading and biochemical signaling both control tissue healing. This has led some researchers to consider using a technique based on tension regulation at the suture line for obtaining good healing. However, it is unknown how they interact and to what extent mechanics control biochemistry. This review will open the way for understanding the interplay between mechanical loading and the process of tendon healing.

Menopause, estrogens and frailty

The controversy surrounding the results from the Women's Health Initiative (WHI) trials published a decade ago caused a significant decline in the use of menopausal hormone replacement therapy. However, these results have been vehemently contested and several lines of evidence suggest that in perimenopausal and non-obese women, estrogen therapy may indeed be of benefit. There is ample proof that menopause causes a loss of musculoskeletal tissue mass and quality, thereby causing a loss of health and quality of life. There is also solid evidence that hormone replacement therapy in itself prevents most of these effects in connective tissue in itself. Besides the independent, direct effects on the musculoskeletal tissues, estrogen deficiency also reduces the ability to adequately respond and adapt to external mechanical and metabolic stressors, e.g. exercise, which are otherwise the main stimuli that should maintain musculoskeletal integrity and metabolic function. Thus, normophysiological estrogen levels appear to exert a permissive effect on musculoskeletal adaptations to loading, thereby likely improving the outcome of rehabilitation following critical illness, musculoskeletal trauma or orthopedic surgical therapy. These effects add to the evidence supporting the use of estrogen therapy, particularly accelerated gain of functional capacity and independence following musculoskeletal disuse.

Effect of acute exercise on patella tendon protein synthesis and gene expression

Evidence suggests that habitual loading can result in patellar tendon hypertrophy, especially at the proximal and distal parts of the patellar tendon. The underlying protein kinetic changes and its regulation remains controversial and human data, investigating this topic, are limited. The present study investigated how acute exercise affects growth factor production and collagen fractional synthetic rate in patellar tendon tissue from patients undergoing an anterior cruciate ligament reconstruction operation. The operation was performed by use of the bone-patellar tendon-bone method under spinal anesthesia.

Twelve subjects were randomized to one of two groups: a control group or an exercise group (1-hr unilateral knee-extension 67% of W_max 24 hours before operation). Two hours before the anterior cruciate ligament operation a flooding-dose of L-[1-¹³C]proline was given. Tissue from the most proximal part of the patellar tendon was obtained during the operation. Tendon collagen fractional synthetic rate and mRNA concentrations of TGF-β-1, CTGF, and type I and III collagen were measured.

CTGF and type I collagen expression were higher in the exercise group compared to the control group (p < 0.05). Type III collagen expression (p = 0.11), TGF-β-1 expression (p = 0.34), and collagen fractional synthetic rate (p = 0.26) did not differ between groups.

Although the expression of CTGF and type I collagen were higher, the patellar tendon collagen fractional synthetic rate was not correspondingly higher after exercise. The elevated CTGF expression in the exercise group indicates that the TGF-beta pathway could be an important link between mechanical loading and stimulation of tendon tissue type I collagen expression.

Impact of oral contraceptive use and menstrual phases on patellar tendon morphology, biochemical composition, and biomechanical properties in female athletes

Sex differences exist with regards to ligament and tendon injuries. Lower collagen synthesis has been observed in exercising women vs. men, and in users of oral contraceptives (OC) vs. nonusers, but it is unknown if OC will influence tendon biomechanics of women undergoing regular training. Thirty female athletes (handball players, 18-30 yr) were recruited: 15 long-term users of OC (7.0 ± 0.6 yr) and 15 nonusers (>5 yr). Synchronized values of patellar tendon elongation (obtained by ultrasonography) and tendon force were sampled during ramped isometric knee extensor maximum voluntary contraction to estimate mechanical tendon properties. Furthermore, tendon cross-sectional area and length were measured from MRI images, and tendon biopsies were obtained for analysis of tendon fibril characteristics and collagen cross-linking. Overall, no difference in tendon biomechanical properties, tendon fibril characteristics, or collagen cross-linking was observed between the OC users and nonusers, or between the different phases of the menstrual cycle. In athletes, tendon cross-sectional area in the preferred jumping leg tended to be larger than that in the contralateral leg (P = 0.09), and a greater absolute (P = 0.01) and normalized tendon stiffness (P = 0.02), as well as a lower strain (P = 0.04), were observed in the jumping leg compared with the contralateral leg. The results indicate that long-term OC use or menstrual phases does not influence structure or mechanical properties of the patellar tendon in female team handball athletes.

Changes in serum collagen markers, IGF-I, and knee joint laxity across the menstrual cycle

Variations in serum markers of collagen production (CICP) and degradation (ICTP), insulin-like growth factor I (IGF-I) and anterior knee laxity (AKL) were measured in 20 women [10 with spontaneous cycles (eumenorrheic), 10 using oral contraceptives] over 5 consecutive days at menses (M1-M5, 1st pill week), the initial estrogen rise near ovulation (O1-O5, 2nd pill week), the initial progesterone rise of the early luteal phase (EL1-EL5, 3rd pill week) and post-progesterone peak of the late luteal phase (LL1-LL5, 4th pill week). ICTP was higher in oral contraceptive women (5.3 ± 1.7 vs. 3.7 ± 1.3 µg/L; p = 0.030), primarily during days near ovulation and the early luteal phase when concentrations decreased in eumenorrheic women (p = 0.04). IGF-I concentrations increased during menses then decreased and remained lower during the early and late luteal phase in oral contraceptive women, resulting in lower concentrations compared to eumenorrheic women at EL2 and LL1 (p = 0.03). CICP decreased in early and late luteal days (p <0.01), and there was a trend toward lower concentrations in eumenorrheic versus oral contraceptive women (85.7 ± 35.7 ng/ml vs. 123.2 ± 49.8 ng/ml; p = 0.07). Lower CICP and greater IGF-I concentrations predicted greater AKL across the 20 cycle days in both groups (R(2)  = 0.310 and 0.400). Sex hormone concentration changes across the menstrual cycle are of sufficient magnitude to influence collagen metabolism, and may indirectly influence knee structure and function.

IGF-I measurement across blood, interstitial fluid, and muscle biocompartments following explosive, high-power exercise

Insulin-like growth factor-I (IGF-I) resides across different biocompartments [blood, interstitial fluid (ISF), and muscle]. Whether circulating IGF-I responses to exercise reflect local events remains uncertain. We measured the IGF-I response to plyometric exercise across blood, ISF, and muscle biopsy from the vastus lateralis. Twenty volunteers (8 men, 12 women, 22 ± 1 yr) performed 10 sets of 10 plyometric jump repetitions at a 40% 1-repetition maximum. Blood, ISF, and muscle samples were taken pre- and postexercise. Circulating IGF-I increased postexercise: total IGF-I (preexercise = 546 ± 42, midexercise = 585 ± 43, postexercise = 597 ± 45, +30 = 557 ± 42, +60 = 536 ± 40, +120 = 567 ± 42 ng/ml; midexercise, postexercise, and +120 greater than preexercise, P < 0.05); Free IGF-I (preexercise = 0.83 ± 0.09, midexercise = 0.78 ± 0.10, postexercise = 0.79 ± 0.11, +30 = 0.93 ± 0.10, +60 = 0.88 ± 0.10, + 120 = 0.91 ± 0.11 ng/ml; +30 greater than all other preceding time points, P < 0.05). No exercise-induced changes were observed for ISF IGF-I (preexercise = 2.35 ± 0.29, postexercise = 2.46 ± 0.35 ng/ml). No changes were observed for skeletal muscle IGF-I protein, although IGF-I mRNA content increased ∼40% postexercise. The increase in circulating total and free IGF-I was not correlated with increases in ISF IGF-I or muscle IGF-I protein content. Our data indicate that exercise-induced increases in circulating IGF-I are not reflective of local IGF-I signaling.

The soy isoflavone genistein inhibits the reduction in Achilles tendon collagen content induced by ovariectomy in rats

The objective of this study was to evaluate the effects of genistein and moderate intensity exercise on Achilles tendon collagen and cross-linking in intact and ovariectomized (OVX) female Sprague-Dawley rats. Rats were separated into eight groups (n = 9/group): intact or OVX, treadmill exercised or sedentary, genistein-treated (300 mg/kg/day) or vehicle. After 6 weeks, tendons were assayed for the collagen-specific amino acid hydroxyproline and hydroxylyslpyridinoline (HP). Collagen content was not influenced by exercise (P = 0.40) but was lower (P < 0.001) in OVX-vehicle rats compared with intact vehicle rats (OVX: 894 ± 35 μg collagen/mg dry weight; intact: 1185 ± 72 μg collagen/mg dry weight). In contrast, collagen content in OVX rats treated with genistein was greater (P = 0.010, 1198 ± 121 μg collagen/mg dry weight) when compared with untreated rats and was not different from intact rats (P = 0.89). HP content was lower in OVX genistein-treated rats when compared with intact genistein-treated rats, but only within the sedentary animals (P = 0.05, intact-treated: 232 ± 39 mmol/mol collagen; OVX-treated: 144 ± 21 mmol/mol collagen). Our findings suggest that ovariectomy leads to a reduction in tendon collagen, which is prevented by genistein. HP content, however, may not have increased in proportion to the addition of collagen. Genistein may be useful for improving tendon collagen content in conditions of estrogen deficiency.

Effects of transdermal estrogen on collagen turnover at rest and in response to exercise in postmenopausal women

Menopause is associated with loss of collagen content in the skin and tendon as well as accumulation of noncontractile tissue in skeletal muscle. The relative role of hormones and physical activity on these changes is not known. Accordingly, in a randomized, controlled, crossover study we investigated effects of transdermal estrogen replacement therapy (ERT) on type I collagen synthesis in tendon and skeletal muscle in 11 postmenopausal women. Patches with estrogen (Evorel) were placed on the skin above the patellar tendons and compared with no patch (control period). On day 2 all subjects performed one-legged exercise, and thereafter the exercised leg (EX leg) was compared with the nonexercised leg (Rest leg). Microdialysis catheters were placed in front of the patellar tendons and in the vastus lateralis muscle of both legs at days 3 and 5. The collected dialysate was analyzed for procollagen type I NH(2)-terminal propeptide (PINP), insulin-like growth factor I (IGF-I), and interleukin-6 (IL-6). Neither loading (Rest leg vs. EX leg) nor treatment (control vs. ERT) influenced peritendinous PINP, whereas combined exercise and ERT enhanced muscle PINP after 72 h (interaction between loading and treatment P = 0.008). In neither skeletal muscle nor peritendinous fluid were IGF-I and IL-6 influenced by treatment or exercise. In conclusion, ERT was associated with enhanced synthesis of type I collagen in the skeletal muscle in response to acute exercise. In perspective, this indicates that the availability of estrogen in postmenopausal women is important for repair of muscle damage or remodeling of the connective tissue within the skeletal muscle after exercise.

Local administration of insulin-like growth factor-I (IGF-I) stimulates tendon collagen synthesis in humans

Collagen is the predominant structural protein in tendons and ligaments, and can be controlled by hormonal changes. In animals, injections of insulin-like growth factor I (IGF-I) has been shown to increase collagen synthesis in tendons and ligaments and to improve structural tissue healing, but the effect of local IGF-I administration on tendon collagen synthesis in human has not been studied. The purpose of this study was to study whether local injections of IGF-I would have a stimulating effect on tendon collagen synthesis. Twelve healthy nonsmoking men [age 62 ± 1 years (mean ± SEM), BMI 27 ± 1] participated. Two injections of either human recombinant IGF-I (0.1 mL Increlex©) or saline (control) into each patellar tendon were performed 24-h apart, respectively. Tendon collagen fractional synthesis rate (FSR) was measured by stable isotope technique in the hours after the second injection. Simultaneously, interstitial peritendinous (IGF-I) and [procollagen type I N-terminal propeptide (PINP)], as a marker for type I collagen synthesis, were determined by microdialysis technique. Tendon collagen FSR and PINP were significantly higher in the IGF-I leg compared with the control leg (P < 0.05). In conclusion, local IGF-I administration can directly enhance tendon collagen synthesis both within and around the human tendon tissue.

The effect of mild symptomatic patellar tendinopathy on the quadriceps contractions and the Fente motion in elite fencers

To investigate how mild symptomatic patellar tendinopathy (PT) affects quadriceps contractions and the Fente motion, this case-control study examined elite fencers who continue to train and play fully with mild tendon pains. Twenty-four elite fencers (10 women) with mild symptomatic PT and 24 controls (10 women) participated in the study. Concentric/eccentric isokinetic strength of the quadriceps was tested, and peak torque and total work were recorded. Kinematic data from the knee during the Fente motion were collected. The first analysis period (P1) was after heel contact to the maximal flexion of the knee, and the second (P2) was right after P1 to heel-off. Normalized peak torque and work of concentric/eccentric contractions were not significantly different. Affected fencers demonstrated significantly reduced angular velocities at P2 (p = 0.042). The male fencers did not demonstrate any differences. The affected female fencers demonstrated significantly weaker concentric peak torque at 60°·s(-1) (p = 0. 009) and 180°·s(-1) (p = 0.047) and less concentric work at 60°·s(-1) (p = 0.020). They also demonstrated significantly reduced average angular velocities at P2 (p = 0.001). Therefore, mild symptomatic PT seems to have an effect on the isokinetic concentric contraction of the quadriceps and the angular velocity of the knee during the backward Fente motion in elite female fencers who are participating fully in training and competition. Key pointsIt is likely that even mild symptomatic patellar tendinopathy could affect the athletic performances in elite fencers.Elite female fencers are more likely to be affected substantially by symptomatic patellar tendinopathy in their sporting ability than male fencers.Because weak concentric knee extensors may affect the performance in fencing, not only eccentric training for symptomatic patellar tendinopathy but also proper concentric training of the quadriceps may be helpful in a rehabilitation program of elite female fencers who are participating fully in their training and competition.

Effect of alpine skiing training on tendon mechanical properties in older men and women

Strain is one of the parameters determining tendon adaptation to mechanical stimuli. The aim of this study was to test whether the patellar tendon strain induced during recreational alpine skiing would affect tendon mechanical properties in older individuals. Twenty-two older males and females (67 ± 2 years) were assigned to a 12-week guided skiing programme (IG) and 20 aged-matched volunteers served as controls (CG). Patellar tendon mechanical properties and cross-sectional area (CSA) were measured before and after training, with combined dynamometry and ultrasonography scanning. None of the variables changed significantly in the CG after training. In the IG, tendon stiffness and Young's modulus were increased (respectively, 14% and 12%, P<0.01), without any significant change in tendon CSA. In addition, changes in tendon stiffness were blunted in women (9%) compared with men (19%). Serum IGF-1 concentration tended to be lower in women (-19%, P=0.07). These results demonstrate that the mechanical stimulus induced by alpine skiing is sufficient to elicit adaptive changes in patellar tendon mechanical and material properties in older subjects. Furthermore, the present sex-specific adaptations are consistent with previous reports of lower collagen metabolic responsiveness in women and may be underpinned by anthropometric and metabolic differences.

Influence of aerobic cycle exercise training on patellar tendon cross-sectional area in older women

Nine to 12 weeks of resistance exercise training in young individuals induces quadriceps muscle (∼6%) and region-specific patellar tendon (4-6%) hypertrophy. However, 12 weeks of resistance exercise training (∼1 h total exercise time) in older individuals (60-78 years) induces quadriceps muscle hypertrophy (9%) without impacting patellar tendon size. The current study examined if a different loading paradigm using cycle exercise would promote patellar tendon hypertrophy or alter the internal tendon properties, measured with magnetic resonance imaging signal intensity, in older individuals. Nine women (70 ± 2 years) completed 12 weeks of aerobic upright cycle exercise training (∼28 h total exercise time). Aerobic exercise training increased (P < 0.05) quadriceps muscle size (11 ± 2%) and VO2max (30 ± 9%). Mean patellar tendon cross-sectional area (CSA) (2 ± 1%) and signal intensity (-1 ± 2%) were unchanged (P > 0.05) over the 12 weeks of training. Region-specific CSA was unchanged (P > 0.05) at the proximal (-1 ± 3%) and mid regions (2 ± 2%) of the tendon but tended (P = 0.069) to increase at the distal region (5 ± 3%). Region-specific signal intensity differed along the tendon but was unchanged (P > 0.05) with training. Although more studies are needed, exercise-induced patellar tendon hypertrophy, compared with skeletal muscle, appears to be attenuated in older individuals, while the loading pattern associated with aerobic exercise seems to have more impact than resistance exercise in promoting patellar tendon hypertrophy.

Effect of administration of oral contraceptives on the synthesis and breakdown of myofibrillar proteins in young women

Oral contraceptive (OC) treatment has an inhibiting effect on protein synthesis in tendon and muscle connective tissue. We aimed to investigate whether OC influence myofibrillar protein turnover in young women. OC-users (24±2 years; Lindynette® n=7, Cilest® n=4) and non-OC-users (controls, 24±4 years n=12) performed one-legged kicking exercise. The next day, the myofibrillar protein fractional synthesis rate (FSR) was measured using stable isotopic tracers ((13)C-proline) while the subjects were fed standardized nutrient drinks. Simultaneously, a marker for myofibrillar protein breakdown, 3-methyl-histidine (3-MH), was measured in the interstitial fluid of the vastus lateralis. Measurements were performed in both legs. In general, myofibrillar protein FSR was lower in OC-users (two-way analysis of variance, P<0.05), although the difference seemed to depend on the OC type. Interstitial 3-MH in the skeletal muscle was not different between groups and did not vary by OC type. Exercise did not change myofibrillar protein FSR or 3-MH concentrations. Serum androstenedione and bioavailability of testosterone were lower in OC-users. In conclusion, the results indicate that the use of OC has an inhibiting effect on myofibrillar protein synthesis and the magnitude of the effect may depend on the type of OC. In contrast, there was no effect of OC on myofibrillar protein breakdown in the fed state.

The role of exercise intensity in the bone metabolic response to an acute bout of weight-bearing exercise

We compared the effects of exercise intensity (EI) on bone metabolism during and for 4 days after acute, weight-bearing endurance exercise. Ten males [mean ± SD maximum oxygen uptake (Vo(2max)): 56.2 ± 8.1 ml·min(-1)·kg(-1)] completed three counterbalanced 8-day trials. Following three control days, on day 4, subjects completed 60 min of running at 55%, 65%, and 75% Vo(2max). Markers of bone resorption [COOH-terminal telopeptide region of collagen type 1 (β-CTX)] and formation [NH(2)-terminal propeptides of procollagen type 1 (P1NP), osteocalcin (OC), bone-alkaline phosphatase (ALP)], osteoprotegerin (OPG), parathyroid hormone (PTH), albumin-adjusted calcium (ACa), phosphate (PO(4)), and cortisol were measured during and for 3 h after exercise and on four follow-up days (FU1-FU4). At 75% Vo(2max), β-CTX was not significantly increased from baseline by exercise but was higher compared with 55% (17-19%, P < 0.01) and 65% (11-13%, P < 0.05) Vo(2max) in the first hour postexercise. Concentrations were decreased from baseline in all three groups by 39-42% (P < 0.001) at 3 h postexercise but not thereafter. P1NP increased (P < 0.001) during exercise only, while bone-ALP was increased (P < 0.01) at FU3 and FU4, but neither were affected by EI. PTH and cortisol increased (P < 0.001) with exercise at 75% Vo(2max) only and were higher (P < 0.05) than at 55% and 65% Vo(2max) during and immediately after exercise. The increases (P < 0.001) in OPG, ACa, and PO(4) with exercise were not affected by EI. Increasing EI from 55% to 75% Vo(2max) during 60 min of running resulted in higher β-CTX concentrations in the first hour postexercise but had no effect on bone formation markers. Increased bone-ALP concentrations at 3 and 4 days postexercise suggest a beneficial effect of this type of exercise on bone mineralization. The increase in OPG was not influenced by exercise intensity, whereas PTH was increased at 75% Vo(2max) only, which cannot be fully explained by changes in serum calcium or PO(4) concentrations.

Estrogen receptor expression in posterior tibial tendon dysfunction: a pilot study

BACKGROUND

The pathophysiology of posterior tibial tendon dysfunction (PTTD) is poorly understood. It has been theorized that changes in hormone physiology may be a factor influencing tendon health. Estrogen's influence on the fibroblast has been studied in other musculoskeletal tissues. Gender differences in anterior cruciate ligament (ACL) injuries have been studied and it has been discovered that the Estrogen receptor (ER) as well as Progesterone receptor (PR) are expressed in the ACL.

MATERIAL AND METHODS

Eight patients with PTTD requiring surgery were enrolled in our pilot study. The mean patient age was 52.4 (range, 18 to 73) years. There were five female and three male patients. Tendon samples were harvested from diseased PTT. Tendon samples harvested from healthy PTT and healthy flexor digitorum longus (FDL) tendon were used as controls. Tendon samples were processed using specific protocols for total RNA isolation from hypocellular, dense connective tissues. ERα and ERβ transcripts were quantified using real time RT-PCR. Quantitative values were obtained from the threshold cycle (Ct) number at which the increase in fluorescent signal associated with an exponential increase of PCR products can be detected.

RESULTS

Transcripts of both ERα and ERβ were reproducibly detected in RNA samples isolated from our tendon samples. There was no difference in receptor expression between diseased and control tendon samples. There was no difference in receptor expression between male and female patients.

CONCLUSION

We found that the tenocyte of the PTT and FDL tendons express ERα and ERβ. Normal and diseased tendons of both male and female patients expressed both estrogen receptors.

CLINICAL RELEVANCE

Identifying ERα and ERβ gene expression in the fibroblast was an initial step in discovering whether tenocytes are targets for estrogen function. Estrogen receptors were identified indirectly by measuring receptor gene expression but we were unable to show a significant difference between diseased and control tendons.

Circulating bioactive and immunoreactive IGF-I remain stable in women, despite physical fitness improvements after 8 weeks of resistance, aerobic, and combined exercise training

Insulin-like growth factor-I (IGF-I) is regulated by a number of IGF-binding proteins (IGFBPs) and proteases that influence IGF-I bioactivity. A specific IGF-I kinase receptor activation assay (KIRA) has been developed that determines the ability of IGF-I to activate the IGF-I receptor by quantification of intracellular receptor autophosphorylation on IGF-I binding. KIRA-assessed IGF-I bioactivity has not been utilized within the context of chronic exercise training paradigms. This study measured total and free immunoreactive IGF-I, bioactive IGF-I, and IGFBP-1, -2, and -3 before (Pre), during (Mid), and after (Post) 8 wk of exercise training in young, healthy women, who were randomized into one of four groups: control ( n = 10), resistance ( n = 18), aerobic ( n = 13), and combined ( n = 15) exercise training. The training programs were effective in improving physical fitness specific to the exercise mode engaged in: increases were observed for lean mass (∼2%), aerobic fitness (6–7%), and upper (20–24%) and lower (15–48%) body strength (all P values < 0.05). By contrast, no time, group, or interaction effects were observed for the circulating IGF-I system, as immunoreactive total (Pre = 264 ± 16 μg/l; Mid = 268 ± 17 μg/l; Post = 271 ± 17 μg/l), free (Pre = 0.70 ± 0.1 μg/l; Mid = 0.63 ± 0.1 μg/l; Post = 0.63 ± 0.2 μg/l) and bioactive (Pre = 2.35 ± 0.3 μg/l; Mid = 2.25 ± 0.3 μg/l; Post = 2.33 ± 0.3 μg/l) IGF-I were unchanged throughout the study. All IGFBP measures were also unchanged. We conclude that increased lean mass, aerobic fitness, and upper and lower body strength resulting from an 8-wk exercise training programs can occur without concomitant increases in either circulating bioactive or immunoreactive IGF-I, as well as associated IGFBPs. In terms of reflecting positive anabolic neuromuscular outcomes, these data do not support a role for endocrine-derived IGF-I.

Effect of estrogen on tendon collagen synthesis, tendon structural characteristics, and biomechanical properties in postmenopausal women

The knowledge about the effect of estradiol on tendon connective tissue is limited. Therefore, we studied the influence of estradiol on tendon synthesis, structure, and biomechanical properties in postmenopausal women. Nonusers (control, n = 10) or habitual users of oral estradiol replacement therapy (ERT, n = 10) were studied at rest and in response to one-legged resistance exercise. Synthesis of tendon collagen was determined by stable isotope incorporation [fractional synthesis rate (FSR)] and microdialysis technique (NH2-terminal propeptide of type I collagen synthesis). Tendon area and fibril characteristics were determined by MRI and transmission electron microscopy, whereas tendon biomechanical properties were measured during isometric maximal voluntary contraction by ultrasound recording. Tendon FSR was markedly higher in ERT users ( P < 0.001), whereas no group difference was seen in tendon NH2-terminal propeptide of type I collagen synthesis ( P = 0.32). In ERT users, positive correlations between serum estradiol (s-estradiol) and tendon synthesis were observed, whereas change in tendon synthesis from rest to exercise was negatively correlated to s-estradiol. Tendon area, fibril density, fibril volume fraction, and fibril mean area did not differ between groups. However, the percentage of medium-sized fibrils was higher in ERT users ( P < 0.05), whereas the percentage of large fibrils tended to be greater in control ( P = 0.10). A lower Young's modulus (GPa/%) was found in ERT users ( P < 0.05). In conclusion, estradiol administration was associated with higher tendon FSR and a higher relative number of smaller fibrils. Whereas this indicates stimulated collagen turnover in the resting state, collagen responses to exercise were negatively associated with s-estradiol. These results indicate a pivotal role for estradiol in maintaining homeostasis of female connective tissue.

Combination of hormone replacement therapy and high physical activity is associated with differences in Achilles tendon size in monozygotic female twin pairs

Estrogen concentration has been suggested to play a role in tendon abnormalities and injury. In physically active postmenopausal women, hormone replacement therapy (HRT) has been suggested to decrease tendon diameter. We hypothesized that HRT use and physical activity are associated with Achilles tendon size and tissue structure. The study applied cotwin analysis of fourteen 54- to 62-yr-old identical female twin pairs with current discordance for HRT use for an average of 7 yr. Achilles tendon thickness and cross-sectional areas were determined by ultrasonography, and tendon structural organization was analyzed from the images using linear discriminant analysis (LDA). Maximal voluntary and twitch torques from plantar flexor muscles were measured. Serum levels of estradiol, estrone, testosterone, and sex hormone binding globulin were analyzed. Total daily metabolic equivalent score (MET-h/day) was calculated from physical activity questionnaires. Results showed that, in five physically active (MET > 4) pairs, the cotwins receiving HRT had greater estradiol level ( P = 0.043) and smaller tendon cross-sectional area than their sisters (63 vs. 71 mm2, P = 0.043). Among all pairs, Achilles tendon thickness and cross-sectional area did not significantly differ between HRT using and nonusing twin sisters. Intrapair correlation for Achilles tendon thickness was high, despite HRT use discordance ( r = 0.84, P < 0.001). LDA distinguished different tendon structure only from two of six examined twin pairs who had a similar level of physical activity. In conclusion, the effect of HRT on Achilles tendon characteristics independent of genetic confounding may be present only in the presence of sufficient physical activity. In physically active twin pairs, the higher level of estrogen seems to be associated with smaller tendon size.

Insulin-like growth factor-I as a candidate metabolic biomarker: military relevance and future directions for measurement

Insulin-like growth factor (IGF)-I is a ubiquitous peptide hormone involved in a host of critical physiological processes (e.g., protein synthesis and glucose homeostasis) and has been suggested to be a biomarker reflecting health and metabolic status. In most cases (muscle, bone, tendon, body composition, and cognitive function), elevated IGF-I concentrations are considered beneficial; however, cancer remains a notable exception. While the fact that both increased and decreased IGF-I can be considered reflective of favorable and beneficial health outcomes may appear as a paradox, it is important to emphasize that, in both cases, measured IGF-I concentrations do offer important insight into physiological processes. The effects of military operational field training on the circulating IGF-I system are discussed within the context of novel measurement technologies that (1) are field expedient and (2) provide more meaningful information. Prospective experimental approaches involving physical activity that sample and measure IGF-I in the body's various biocompartments will provide greater insight into the complex role that IGF-I possesses. Minimally invasive technologies that are field expedient, cost-effective, and allow for continuous and real-time feedback will have the greatest likelihood of being adapted and used in military environments.

Exercise training and protein metabolism: influences of contraction, protein intake, and sex-based differences

Muscle contraction during exercise, whether resistive or endurance in nature, has profound affects on muscle protein turnover that can persist for up to 72 h. It is well established that feeding during the postexercise period is required to bring about a positive net protein balance (muscle protein synthesis - muscle protein breakdown). There is mounting evidence that the timing of ingestion and the protein source during recovery independently regulate the protein synthetic response and influence the extent of muscle hypertrophy. Minor differences in muscle protein turnover appear to exist in young men and women; however, with aging there may be more substantial sex-based differences in response to both feeding and resistance exercise. The recognition of anabolic signaling pathways and molecules are also enhancing our understanding of the regulation of protein turnover following exercise perturbations. In this review we summarize the current understanding of muscle protein turnover in response to exercise and feeding and highlight potential sex-based dimorphisms. Furthermore, we examine the underlying anabolic signaling pathways and molecules that regulate these processes.