Human patellar tendon stress (s), strain (e), stiffness (K), and tensile or Young's modulus (E), are determined in vivo through voluntary isometric contractions monitored with B-mode ultrasonography. The limitations in previous studies are: (1) they have generally not accounted for the fact that the distal attachment of the patellar tendon (the tibial tuberosity) also displaces; thus, they have underestimated e (and, hence, injury risk) while overestimating K; (2) no gender effect has been studied despite the fact that females are seen to have higher incidences of tendon-related injuries. The current investigation therefore aimed to determine the gender specific values of s, e, K, and E of the patellar tendon while also accounting for distal displacement of the patellar tendon. Healthy young males (aged 23.1 AE 1.3 years, n ¼ 10) and females (aged 21.3 AE 0.9 years, n ¼ 10) were tested. The maximal e of the young males was $5-10% higher than that reported in earlier literature. Average female versus male values for e, s, K, and E, taken at the same force level as the males for comparison purposes, were respectively 10.6 AE 1.0 versus 9.0 AE 1.0%, 36.9 AE 1.4 versus 28.9 AE 0.9 MPa, 1053 AE 108 versus 1652 AE 216 N Á mm À1 , and 0.61 AE 0.08 versus 0.68 AE 0.10 GPa (p < 0.05). There are gender differences in tendon structural and mechanical properties. The current methodology may be useful in a clinical context where early prediction of injury risk and/or monitoring of reconstructed tendon needs to be an accurate, objective, and reliable method if optimal functionality is to be achieved. ß

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 x mm(-1)) and isometric groups (61.6%; 43.9 +/- 2.5 to 71.0 +/- 7.4 N x 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.

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 AE 1 (SEM), n ¼ 17] and male (22 years AE 1, n ¼ 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 Young's modulus (e) 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 e (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. ß

This study compared the effects of low vs. high intensity training on tendon properties in an elderly population. Participants were pair-matched (gender, habitual physical activity, anthropometrics, and baseline knee extension strength) and then randomly assigned to low (LowR, i.e.,~40 % 1RM) or high (High R, i.e.,~80 % 1RM) intensity resistance training programmes for 12 weeks, 3× per week (LowR, n=9, age 74±5 years; HighR, n=8, age 68 ±6 years). Patellar tendon properties (stiffness [K], Young's modulus [YM], cross-sectional area [T CSA ], and tendon length [T L ]) were measured pre and post training using a combination of magnetic resonance imaging (MRI), B-mode ultrasonography, dynamometry, electromyography and ramped isometric knee extensions. With training K showed no significant change in the LowR group while it incremented by 57.7 % in the HighR group (p<0.05). The 51.1 % group difference was significant (p<0.05). These differences were still apparent when the data was normalized for T CSA and T L , i.e., significant increase in YM post-intervention in HighR (p<0.05), but no change in LowR. These findings suggest that when prescribing exercise for a mixed genders elderly population, exercise intensities of ≤40 % 1RM may not be sufficient to affect tendon properties.

No abstract

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 ¼ 27, aged 72 AE 1 years, women n ¼ 28, aged 70 AE 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 AE 29.2 vs. women 502.9 AE 44.9 Nmm À1 ) or in Young's modulus (elderly men 0.32 AE 0.02 vs. women 0.36 AE 0.04 GPa). This elderly group had similar tendon structural and mechanical properties. The comparable characteristics in genderspecific 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. Keywords: aging; gender differences; patellar tendon; stiffness; Young's modulusIn the last 30 years the proportion of the population aged 65 years or more has increased to 16% in the UK and this increase is set to continue (The Office for National Statistics, 2006). Approximately one-third of people aged over 65 fall at least once a year, and about half of these do so recurrently, leading to injury and subsequent decrease in quality of life, and in many cases death. 1 Elderly women exhibit a higher risk of falling than their male counterparts, 2,3 and most falls occur after a loss of stability in a forward direction such as tripping while walking. 2 In order to maintain balance individuals require information concerning the orientation of the body in space and the geometry of the body. In humans this information is obtained via the complex interactions of sensory systems (primarily the somatosensory, visual, and vestibular systems) and motor systems. 4 Aging results in a decline in the function of these systems and their interaction, which has been related to reduced balance ability and thus increased fall risk. [5][6][7]

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.

No abstract