Sources of Variability in Musculo-Articular Stiffness Measurement

The assessment of musculo-articular stiffness (MAS) with the free-oscillation technique is a popular method with a variety of applications. This study examined the sources of variability (load applied and frequency of oscillation) when MAS is assessed.Over two testing occasions, 14 healthy men (27.7±5.2 yr, 1.82±0.04 m, 79.5±8.4 kg) were measured for isometric maximum voluntary contraction and MAS of the knee flexors using submaximal loads relative to the individual's maximum voluntary contraction (MAS%MVC) and a single absolute load (MASABS).As assessment load increased, MAS%MVC (coefficient of variation (CV) = 8.1-12.1%; standard error of measurement (SEM) = 51.6-98.8 Nm-1) and frequency (CV = 4.8-7.0%; SEM = 0.060-0.075 s-1) variability increased consequently. Further, similar levels of variability arising from load (CV = 6.7%) and frequency (CV = 4.8-7.0%) contributed to the overall MAS%MVC variability. The single absolute load condition yielded better reliability scores for MASABS (CV = 6.5%; SEM = 40.2 Nm-1) and frequency (CV = 3.3%; SEM = 0.039 s-1).Low and constant loads for MAS assessment, which are particularly relevant in the clinical setting, exhibited superior reliability compared to higher loads expressed as a percentage of maximum voluntary contraction, which are more suitable for sporting situations. Appropriate sample size and minimum detectable change can therefore be determined when prospective studies are carried out. © 2013 Ditroilo et al

The effect of water-based plyometric training on vertical stiffness and athletic performance

© 2018 Sporri et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Since higher vertical stiffness is related to superior athletic performance, training has traditionally been aimed at augmenting this variable to enhance neuromuscular output. However, research has linked elevated stiffness with increased injury risk, therefore, this study examined the effect of a novel training intervention on vertical stiffness and athletic performance. Vertical stiffness, jump performance and athletic performance were assessed in two randomly allocated groups, prior to, and following, an eight-week period. One group was exposed to a training intervention involving aqua-based plyometrics (n = 11) over the 8 weeks while the other acted as a control group (n = 9). The training intervention involved hopping, jumping and bounding in water at a depth of 1.2m whilst control participants performed their normal training. There were no significant changes in vertical stiffness in either group. Countermovement jump height and peak power significantly increased within the aqua plyometric group (p < 0.05). Athletic performance markers improved in the aqua plyometric group as measured using an agility and a 5-bound test exhibiting superior values at the post-test (p < 0.05). The results suggest that an aqua plyometric training program can enhance athletic performance without elevating stiffness. The increase in athletic performance is likely due to a reduction in ground reaction forces created by the buoyancy of the water, causing a shorter amortization phase and a more rapid application of concentric force. The findings from this study can inform exercise professionals and medical staff regarding the ability to enhance neuromuscular performance without elevating vertical stiffness. This has implications for improving athletic performance while concurrently minimising injury risk

Reduced Radial Displacement of the Gastrocnemius Medialis Muscle After Electrically Elicited Fatigue

Context:&nbsp;Assessments of skeletal muscle functional capacity often necessitate maximal contractile effort, which exacerbates muscle fatigue or injury. Tensiomyography (TMG) has been investigated as a means to assess muscle contractile function following fatigue; however observations have not been contextualised by concurrent physiological measures. Objective:&nbsp;The aim of the present investigation was to measure peripheral fatigue-induced alterations in mechanical and contractile properties of the plantar flexor muscles through non-invasive TMG concurrently with maximal voluntary contraction (MVC) and passive muscle tension (PMT) in order to validate TMG as a gauge of peripheral fatigue. Design:&nbsp;Pre- and post-test intervention with control. Setting:&nbsp;University laboratory. Participants:&nbsp;Twenty-one healthy male volunteers. Interventions:&nbsp;Subjects plantar flexors were tested for TMG parameters, along with MVC and PMT, before and after either a 5 minute rest period (control) or a 5 minute electrical stimulation intervention (fatigue). Main Outcome Measures:&nbsp;Temporal (contraction velocity) and spatial (radial displacement) contractile parameters of the Gastrocnemius Medialis were recorded through TMG. MVC was measured as an indicator of muscle fatigue and PMT was measured to assess muscle stiffness. Results:&nbsp;Radial displacement demonstrated a fatigue-associated reduction (3.3 &plusmn; 1.2 vs. 4.0 &plusmn; 1.4 mm vs, p=0.031), while contraction velocity remained unaltered. Additionally, MVC significantly declined by 122.6 &plusmn; 104 N (p&lt;0.001) following stimulation (fatigue). PMT was significantly increased following fatigue (139.8 &plusmn; 54.3 vs. 111.3 &plusmn; 44.6 N, p=0.007).&nbsp; Conclusion: TMG successfully detected fatigue, evident from reduced MVC, by displaying impaired muscle displacement, accompanied by elevated PMT. TMG could be useful in establishing fatigue status of skeletal muscle without exacerbating the functional decrement of the muscle

Physiological responses to pedaling on a water stationary bike at different immersion heights

Only a few studies[1-4] have investigated oxygen consumption (V’O2) and heart rate (HR) responses to pedaling on a stationary bike in water (WSB), while literature is still lacking on the effects elicited by variations in immersion depth. 14 subjects (8 M, 6 F, age 30±6y, weight 67±14kg, BMI 22.8±2.3kg/m2, fat mass 21,4±3%) performed 2 testing sessions and 2 exercise sessions: i) dry-land incremental exercise test (cycle-ergometer) to age-predicted maximum HR (HR); ii) underwater (hip-height) incremental exercise test (on a WSB) to exhaustion; iii/iv) two 2-stage (18-minutes each) underwater pedaling exercises on a WSB (Aqquatix S.r.l., Italy) at 2 different immersion heights (armpit/hip). Breath-by-breath V’O2 and beat-by-beat HR were recorded continuously throughout dry-land sessions. The intensities of the exercise sessions were 45%-55% (stage#1) and 70%-80% (stage#2) of the underwater V’O2 peak (a metronome was set at the V’O2 peak pedaling rate). A repeated-measures (2 exercise intensities) 2-way (armpit/hip heights) ANOVA was performed on each variable and the Bonferroni test was used for post-hoc comparisons. Compared to the hip-height condition, pedaling immersed at the armpit level elicited significantly lower V’O2 and HR (significant solely at high-intensity for HR) responses, either exercising at high (25.5±4.6 vs. 29.1±4.8 mL∙kg-1∙min-1; 127±14 vs. 140±19 beats∙min-1) or low (17.9±3.6 vs. 20.1±3.6 mL∙kg-1∙min-1; 105±16 vs. 110±15 beats∙min-1) intensity. While peak V’O2 didn’t differ significantly between dry-land and underwater tests (36.2±5.4 vs. 38.8±5.8 mL∙kg-1∙min-1), mean HRs at both intensities and both water heights were significantly lower when expressed as percentage of the HR resulting from the underwater test to exhaustion, rather than applying the 220-age prediction equation.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Functional balance performance in aging: evidence of moderated prediction by strength and power

Age-related reductions in strength and power are considered to negatively impact balance control, but the existence of a direct association is still an issue of debate (Orr, 2010). This is possibly due to the complexity of its assessment which may involve quantitative measurements of postural sway or functional balance tasks (Granacher et al., 2012). The present work questions whether postural balance interacts with strength and power in determining functional balance performance. Fifty-seven healthy 65 to 75 year old individuals performed tests of dynamic functional balance (chair rise, walking speed under different conditions) and of strength, power and static postural balance. Results showed that functional balance performances were generally predicted by strength and power and, additionally, by postural balance when conditions required postural adjustments. Interactive effects of postural balance and strength were found, indicating that good postural balance facilitates the utilisation of strength to better perform complex functional balance tasks

Tibial impacts and muscle activation during walking, jogging and running when performed overground, and on motorised and non-motorised treadmills.

Purpose To examine tibial acceleration and muscle activation during overground (OG), motorised treadmill (MT) and non-motorised treadmill conditions (NMT) when walking, jogging and running at matched velocities. Methods An accelerometer recorded acceleration at the mid-tibia and surface EMG electrodes recorded rectus femoris (RF), semitendinosus (ST), tibialis anterior (TA) and soleus (SL) muscle activation during OG, MT and NMT locomotion whilst walking, jogging and running. Results The NMT produced large reductions in tibial acceleration when compared with OG and MT conditions across walking, jogging and running conditions. RF EMG was small-moderately higher in the NMT condition when compared with the OG and MT conditions across walking, jogging and running conditions. ST EMG showed large and very large increases in the NMT when compared to OG and MT conditions during walking whilst SL EMG found large increases on the NMT when compared to OG and MT conditions during running. The NMT condition generated very large increases in step frequency when compared to OG and MT conditions during walking, with large and very large decreases during jogging and very large decreases during running. Conclusions The NMT generates large reductions in tibial acceleration, moderate to very large increases in muscular activation and large to very large decreases in cycle time when compared to OG and MT locomotion. Whilst this may decrease the osteogenic potential of NMT locomotion, there may be uses for NMTs during rehabilitation for lower limb injuries

Assessment of post-competition peak blood lactate in male and female master swimmers aged 40–79 years and its relationship with swimming performance

The main purpose of this study was to measure the postcompetition blood lactate concentration ([La]b) in master swimmers of both sexes aged between 40 and 79 years in order to relate it to age and swimming performance. One hundred and eight swimmers participating in the World Master Championships were assessed for [La]b and the average rate of lactate accumulation (La’;mmol l-1 s-1) was calculated. In addition, 77 of them were also tested for anthropometric measures. When the subjects were divided into 10-year age groups, males exhibited higher [La]b than women (factorial ANOVA, P < 0.01) and a steeper decline with ageing than female subjects. Overall, mean values (SD) of [La]b were 10.8 (2.8), 10.3 (2.0), 10.3 (1.9), 8.9 (3.2) mmol l-1 in women, and 14.2 (2.5), 12.4 (2.5), 11.0 (1.6), 8.2 (2.0) mmol l-1 in men for, respectively, 40–49, 50–59, 60–69, 70–79 years’ age groups. When, however, [La]b values were normalised for a ‘‘speed index’’, which takes into account swimming speed as a percentage of world record, these sex-related differences, although still present, were considerably attenuated. Furthermore, the differences in La’ between males and females were larger in the 40–49 age group (0.34 vs 0.20 mmol l-1 s-1 for 50-m distance) than in the 70–79 age group (0.12 vs 0.14 mmol l-1 s-1 for 50-m distance). Different physiological factors, supported by the considered anthropometric measurements, are suggested to explain the results

Assessment of Skeletal Muscle Contractile Properties by Radial Displacement: The Case for Tensiomyography

Skeletal muscle operates as a near-constant volume system; as such muscle shortening during contraction is transversely linked to radial deformation. Therefore, to assess contractile properties of skeletal muscle, radial displacement can be evoked and measured. Mechanomyography measures muscle radial displacement and during the last 20 years, tensiomyography has become the most commonly used and widely reported technique among the various methodologies of mechanomyography. Tensiomyography has been demonstrated to reliably measure peak radial displacement during evoked muscle twitch, as well as muscle twitch speed. A number of parameters can be extracted from the tensiomyography displacement/time curve and the most commonly used and reliable appear to be peak radial displacement and contraction time. The latter has been described as a valid non-invasive means of characterising skeletal muscle, based on fibre-type composition. Over recent years, applications of tensiomyography measurement within sport and exercise have appeared, with applications relating to injury, recovery and performance. Within the present review, we evaluate the perceived strengths and weaknesses of tensiomyography with regard to its efficacy within applied sports medicine settings. We also highlight future tensiomyography areas that require further investigation. Therefore, the purpose of this review is to critically examine the existing evidence surrounding tensiomyography as a tool within the field of sports medicine