The human patellar tendon moment arm assessed in vivo using dual-energy X-ray absorptiometry

Evaluating the effects of hormone therapy termination on skeletal muscle and physical independence in postmenopausal women

OBJECTIVE

In women, the age-related decline in skeletal muscle structure and function is accelerated after menopause, which implicates the role of decreased circulating estrogen levels. Indeed, boosting estrogen, by means of postmenopausal hormone therapy (HT), generally proves beneficial to skeletal muscle. The evidence regarding whether these benefits persist even after cessation of HT is limited, nor is it clear how physical behavior (PB) impacts on benefits. Hence, this exploratory study focused on the interplay between HT administration/cessation, PB and in vivo skeletal muscle structure and function.

METHODS

Fifty healthy women (≥60 y) were included; 19 had an HT administration history (≥9 mo, with now ~8-y hiatus in treatment) and 31 no such history. On seven continuous days, PB data were collected using triaxial accelerometry and analyzed using compositional data analysis. Gastrocnemius medialis muscle volume, architecture, and function were determined using ultrasonography, electromyography, dual x-ray absorptiometry, and dynamometry. Current serum estradiol levels were measured using ELISA.

RESULTS

Only fascicle length and duration of HT administration were positively associated. With respect to PB levels, we found a pattern suggesting greater vitality (higher physical activity and lower sedentarism) in previous HT users, compared with nonusers, despite the two groups currently no longer exhibiting significantly different levels of circulating estradiol.

CONCLUSIONS

After an 8-year hiatus in treatment, HT provides limited advantages in gastrocnemius medialis muscle properties. Interestingly, it perhaps enhances vitality despite prolonged cessation, which in the longer term would facilitate greater physical independence, especially considering the association of sedentary behavior with greater frailty.

The validity and reliability of the Achilles tendon moment arm assessed with dual-energy X-ray absorptiometry, relative to MRI and ultrasound assessments

Dual-energy X-ray absorptiometry (DXA) in single energy mode has been shown to permit the visualisation of bone and soft tissue, such as the patellar tendon through two-dimensional sagittal imaging. However, there is no validated DXA-based measurement of the Achilles tendon moment arm (d_AT). The aims of this study were: 1) to compare in vivo DXA derived measurements of the d_AT at rest against two previously validated methods: tendon excursion (TE) and magnetic resonance imaging (MRI) at three ankle angles (-5°, 0° and +10°). 2) analyse the intra-day reliability of the DXA method at all ankle angles and compare between methods. Twelve healthy adults (mean ± SD: 31.4 ± 9.5 years; 174.0 ± 9.5 cm; 76.2 ± 16.6 kg) participated in this study, involving test-retest DXA scans, ultrasound scans and one MRI scan. The d_AT was defined as the distance from the centre of the calcaneal-tibial joint axis to the Achilles tendon (AT) muscle-tendon line of action. DXA derived d_AT measures were significantly greater than MRI measurements (19.7-24.9%) and were 45.2% significantly larger than the TE method. The test-retest reliability of the DXA technique at 0° was high [CV = 1.38%; ICC = 0.96] and despite the consistently larger d_AT lengths obtained using DXA, MRI and DEXA data were strongly correlated (r = 0.878, p < 0.001). In conclusion, the DXA technique allowed for highly reproducible in vivo d_AT measurement at rest, which has implications for the calculation of AT forces in vivo and the ability to predict the measurement from one tool to the other, thereby providing a novel basis to contrast existing and future studies.

The effects of knee support on the sagittal lower-body joint kinematics and kinetics of deep squats

Little work has been done to examine the deep squat position (>130° sagittal knee flexion). In baseball and softball, catchers perform this squat an average of 146 times per nine-inning game. To alleviate some of the stress on their knees caused by this repetitive loading, some catchers wear foam knee supports.

OBJECTIVES

This work quantifies the effects of knee support on lower-body joint kinematics and kinetics in the deep squat position.

METHODS

Subjects in this study performed the deep squat with no support, foam support, and instrumented support. In order to measure the force through the knee support, instrumented knee supports were designed and fabricated. We then developed an inverse dynamic model to incorporate the support loads. From the model, joint angles and moments were calculated for the three conditions.

RESULTS

With support there is a significant reduction in the sagittal moment at the knee of 43% on the dominant side and 63% on the non-dominant side compared to without support. These reductions are a result of the foam supports carrying approximately 20% of body weight on each side.

CONCLUSION

Knee support reduces the moment necessary to generate the deep squat position common to baseball catchers. Given the short moment arm of the patella femoral tendon, even small changes in moment can have a large effect in the tibial-femoral contact forces, particularly at deep squat angles. Reducing knee forces may be effective in decreasing incidence of osteochondritis dissecans.

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

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

Specific force of the vastus lateralis in adults with achondroplasia

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

Muscle-Tendon Unit Properties during Eccentric Exercise Correlate with the Creatine Kinase Response

Aim: The aim of this paper was to determine whether; (1) patella tendon stiffness, (2) the magnitude of vastus lateralis fascicle lengthening, and (3) eccentric torque correlate with markers of exercise induced muscle damage. Method: Combining dynamometry and ultrasonography, patella tendon properties and vastus lateralis architectural properties were measured pre and during the first of six sets of 12 maximal voluntary eccentric knee extensions. Maximal isometric torque loss and creatine kinase activity were measured pre-damage (-48 h), 48, 96, and 168 h post-damage as markers of exercise-induced muscle damage. Results: A significant increase in creatine kinase (883 ± 667 UL) and a significant reduction in maximal isometric torque loss (21%) was reported post-eccentric contractions. Change in creatine kinase from pre to peak significantly correlated with the relative change in vastus lateralis fascicle length during eccentric contractions (r = 0.53, p = 0.02) and with eccentric torque (r = 0.50, p = 0.02). Additionally, creatine kinase tended to correlate with estimated patella tendon lengthening during eccentric contractions (p < 0.10). However, creatine kinase did not correlate with resting measures of patella tendon properties or vastus lateralis properties. Similarly, torque loss did not correlate with any patella tendon or vastus lateralis properties at rest or during eccentric contractions. Conclusion: The current study demonstrates that the extent of fascicle strain during eccentric contractions correlates with the magnitude of the creatine kinase response. Although at rest, there is no relationship between patella tendon properties and markers of muscle damage; during eccentric contractions however, the patella tendon may play a role in the creatine kinase response following EIMD.

Oral contraceptive pill use and the susceptibility to markers of exercise-induced muscle damage

Purpose

Firstly, to establish whether oral contraceptive pill (OCP) users are more susceptible to muscle damage compared to non-users, and secondly, to establish whether differences can be attributed to differences in patella tendon properties.

Methods

Nine female OCP users and 9 female non-users participated in the investigation. Combining dynamometry, electromyography and ultrasonography, patella tendon properties and vastus lateralis architectural properties were measured pre and during the first of 6 sets of 12 maximal voluntary eccentric knee extensions. Serum oestrogen levels were measured on the 7th day of the pill cycle and the 14th day of menstrual cycle in OCP users and non-users, respectively. Maximal voluntary isometric knee extension torque loss, creatine kinase and muscle soreness were measured 48 h pre-damage, post-damage, and 48, 96 and 168 h post-damage.

Results

Oestrogen levels were significantly lower in OCP users compared to non-users (209 ± 115 and 433 ± 147 pg/ml, respectively, p = 0.004). Proposed determinants of muscle damage, patella tendon stiffness and maximal eccentric torque did not differ between OCP users and non-users. The change in creatine kinase from pre to peak was significantly higher in OCP users compared to non-users (962 ± 968 and 386 ± 474 Ul, respectively, p = 0.016). There were no other differences in markers of muscle damage.

Conclusion

Although our findings suggest that, when compared to non-users, the OCP may augment the creatine kinase response following eccentric exercise, it does not increase the susceptibility to any other markers of muscle damage.

Polymorphisms in PTK2 are associated with skeletal muscle specific force: an independent replication study

PURPOSE

The aim of the study was to investigate two single nucleotide polymorphisms (SNP) in PTK2 for associations with human muscle strength phenotypes in healthy men.

METHODS

Measurement of maximal isometric voluntary knee extension (MVC_KE) torque, net MVC_KE torque and vastus lateralis (VL) specific force, using established techniques, was completed on 120 Caucasian men (age = 20.6 ± 2.3 year; height = 1.79 ± 0.06 m; mass = 75.0 ± 10.0 kg; mean ± SD). All participants provided either a blood (n = 96) or buccal cell sample, from which DNA was isolated and genotyped for the PTK2 rs7843014 A/C and rs7460 A/T SNPs using real-time polymerase chain reaction.

RESULTS

Genotype frequencies for both SNPs were in Hardy-Weinberg equilibrium (X ² ≤ 1.661, P ≥ 0.436). VL specific force was 8.3% higher in rs7843014 AA homozygotes than C-allele carriers (P = 0.017) and 5.4% higher in rs7460 AA homozygotes than T-allele carriers (P = 0.029). No associations between either SNP and net MVC_KE torque (P ≥ 0.094) or peak MVC_KE torque (P ≥ 0.107) were observed.

CONCLUSIONS

These findings identify a genetic contribution to the inter-individual variability within muscle specific force and provides the first independent replication, in a larger Caucasian cohort, of an association between these PTK2 SNPs and muscle specific force, thus extending our understanding of the influence of genetic variation on the intrinsic strength of muscle.

Fat mass and obesity associated (FTO) gene influences skeletal muscle phenotypes in non-resistance trained males and elite rugby playing position

Background

FTO gene variants have been associated with obesity phenotypes in sedentary and obese populations, but rarely with skeletal muscle and elite athlete phenotypes.

Methods

In 1089 participants, comprising 530 elite rugby athletes and 559 non-athletes, DNA was collected and genotyped for the FTO rs9939609 variant using real-time PCR. In a subgroup of non-resistance trained individuals (NT; n = 120), we also assessed structural and functional skeletal muscle phenotypes using dual energy x-ray absorptiometry, ultrasound and isokinetic dynamometry. In a subgroup of rugby athletes (n = 77), we assessed muscle power during a countermovement jump.

Results

In NT, TT genotype and T allele carriers had greater total body (4.8% and 4.1%) and total appendicular lean mass (LM; 3.0% and 2.1%) compared to AA genotype, with greater arm LM (0.8%) in T allele carriers and leg LM (2.1%) for TT, compared to AA genotype. Furthermore, the T allele was more common (94%) in selected elite rugby union athletes (back three and centre players) who are most reliant on LM rather than total body mass for success, compared to other rugby athletes (82%; P = 0.01, OR = 3.34) and controls (84%; P = 0.03, OR = 2.88). Accordingly, these athletes had greater peak power relative to body mass than other rugby athletes (14%; P = 2 x 10^-6).

Conclusion

Collectively, these results suggest that the T allele is associated with increased LM and elite athletic success. This has implications for athletic populations, as well as conditions characterised by low LM such as sarcopenia and cachexia.

Muscle Damage following Maximal Eccentric Knee Extensions in Males and Females

Aim

To investigate whether there is a sex difference in exercise induced muscle damage.

Materials and Method

Vastus Lateralis and patella tendon properties were measured in males and females using ultrasonography. During maximal voluntary eccentric knee extensions (12 reps x 6 sets), Vastus Lateralis fascicle lengthening and maximal voluntary eccentric knee extensions torque were recorded every 10° of knee joint angle (20–90°). Isometric torque, Creatine Kinase and muscle soreness were measured pre, post, 48, 96 and 168 hours post damage as markers of exercise induced muscle damage.

Results

Patella tendon stiffness and Vastus Lateralis fascicle lengthening were significantly higher in males compared to females (p<0.05). There was no sex difference in isometric torque loss and muscle soreness post exercise induced muscle damage (p>0.05). Creatine Kinase levels post exercise induced muscle damage were higher in males compared to females (p<0.05), and remained higher when maximal voluntary eccentric knee extension torque, relative to estimated quadriceps anatomical cross sectional area, was taken as a covariate (p<0.05).

Conclusion

Based on isometric torque loss, there is no sex difference in exercise induced muscle damage. The higher Creatine Kinase in males could not be explained by differences in maximal voluntary eccentric knee extension torque, Vastus Lateralis fascicle lengthening and patella tendon stiffness. Further research is required to understand the significant sex differences in Creatine Kinase levels following exercise induced muscle damage.

Variants within the MMP3 gene and patellar tendon properties in vivo in an asymptomatic population

BACKGROUND/AIM

Gene variants encoding for proteins involved in homeostatic processes within tendons may influence its material and mechanical properties in humans. The purpose of this study was to examine the association between three polymorphisms of the MMP3 gene, (rs679620, rs591058 and rs650108) and patellar tendon dimensional and mechanical properties in vivo.

METHODS

One hundred and sixty, healthy, recreationally-active, Caucasian men and women, aged 18-39 were recruited. MMP3 genotype determined using real-time PCR was used to select 84 participants showing greatest genetic differences to complete phenotype measurements. Patellar tendon dimensions (volume) and functional (elastic modulus) properties were assessed in vivo using geometric modelling, isokinetic dynamometry, electromyography and ultrasonography.

RESULTS

No significant associations were evident between the completely linked MMP3 rs591058 and rs679620 gene variants, and closely linked rs650108 gene variant, and either patellar tendon volume (rs679620, P = 0.845; rs650108, P = 0.984) or elastic modulus (rs679620, P = 0.226; rs650108, P = 0.088). Similarly, there were no associations with the Z-score that combined those dimension and functional properties into a composite value (rs679620, P = 0.654; rs650108, P = 0.390). Similarly, no association was evident when comparing individuals with/without the rarer alleles (P > 0.01 in all cases).

CONCLUSIONS

Patellar tendon properties do not seem to be influenced by the MMP3 gene variants measured. Although these MMP3 gene variants have previously been associated with the risk of tendon pathology, that association is unlikely to be mediated via underlying tendon dimensional and functional properties.