Comparison between Two Different Handgrip Systems and Protocols on Force Reduction in Handgrip Assessment.

INTRODUCTION: Fatigue resistance (FR) can be assessed as the time during which grip strength (GS) drops to 50% of its maximum during a sustained maximal voluntary contraction. For the first time, we compared force-time characteristics during FR test between two different handgrip systems and investigated age- and clinical-related differences in order to verify if a briefer test protocol (i.e., until 75%) could be sufficiently informative. METHODS: A cohort of young healthy controls (Y, <30 y, 24 ± 3 y, 54% women), middle-aged (MA, 30-65 y, 47 ± 11 y, 54% women), and older (OLD, >65 y, 77 ± 7 y, 50% women) community-dwelling persons, and hospitalized geriatric patients (HOSP, 84 ± 5 y, 50% women) performed the FR test. For this purpose, an adapted vigorimeter (original rubber bulb of the Martin Vigorimeter connected to a Unik 5000 pressure gauge) here defined as "pneumatic handgrip system" (Pneu) and Dynamometer G200 system (original Jamar Dynamometer handle with an in-build strength gauge) here defined as "hydraulic handgrip system" (Hydr) were used. Force-time curves were analysed from 100% to 75% and from 75% to 50% of the initial maximal GS during the FR test. The area under the curve (GW) was calculated by integrating the actual GS at each time interval (i.e., 1/5,000 s) and corrected for body weight (GW/body weight). RESULTS: For both systems, we found fair associations between FR100-50 and FR100-75 (Pneu mean difference = 50.1 s [95% CI: 47.9-52.4], r2 = 0.48; Hydr mean difference = 28.4 s [95% CI: 27.0-29.7], r2 = 0.52, all p < 0.001) and also moderate associations between GW(100-50)/body weight and GW(100-75)/body weight (Pneu mean difference = 32.1 kPa*s/kg [95% CI: 30.6-33.6], r2 = 0.72; Hydr mean difference = 8.1 kg*s/kg [95% CI: 7.7-8.6], r2 = 0.68, all p < 0.001). Between MA and OLD, we found a significant age-related difference in the GW results in the first 25% strength decay for Pneu (10.2 ± 0.6 kPa*s/kg against 7.1 ± 1.2 kPa*s/kg, respectively). CONCLUSION: The brief test protocol is valid. Differences within the first 25% strength decay in GW between OLD and HOSP were identified when using Pneu but not when using Hydr. Therefore, a brief FR test protocol using a continuous registration of the strength decay seems to be sufficiently informative in a clinical setting to appraise muscle fatigability, however, only when using a Pneu system.

Muscle fatigability measured with Pneumatic and Hydraulic handgrip systems are not interchangeable.

BACKGROUND: Fatigue resistance (FR) was here defined as the time during which grip strength (GS) drops to 50% of its maximum during sustained contraction. Since different GS systems exist, we compared FR obtained with Pneumatic (Pneu) and Hydraulic (Hydr) handgrip systems. Hand pain induced by both systems was also investigated since this might influence FR-outcomes. METHODS: 618 young controls (Y: reference group), 426 middle-aged (MA) and 234 old community-dwelling adults (OLD), and 50 hospitalized patients (HOSP) participated. FR was recorded with Pneu and Hydr. Grip work corrected for body weight (area under the strength-time curve; GWBW = 0.75 ∗ maximal GS ∗ FR / body weight) was calculated. We corrected for body weight since heavier or more obese participants will have to engage more strength and sustain the effort over time. Thereafter GWBW was expressed as T-scores representing the deviation from the mean score of the sex-specific reference group. Experienced pain, its intensity and whether pain hindered participants to sustain the contraction were questioned. RESULTS: Overall, although significant correlation between FR measured with both systems was found (r = 0.418, p < 0.001), FR measured by Pneu (55.7 ± 35.0 s) was higher compared to Hydr (34.2 ± 18.4 s). There was a proportional difference in FR measured with both systems (R2 = 0.36, p < 0.001), highlighting the longer participants could sustain FR test, the higher the difference in FR measured with both systems. Overall, there was no difference in pain variables between both systems. Independent of sex and system, GWBW deviated less from reference group in MA compared to OLD and HOSP. In OLD, GWBW deviated less from reference group than HOSP, independent of sex and system. CONCLUSION: Participants were unable to sustain the contraction with Hydr as long as with Pneu. Hydr seems less able to identify subjects with higher levels of muscle endurance. Based on the GWBM-scores we can conclude that either system can be used for assessing muscle fatigability, but Pneu may be more sensitive as differences can be detected more easily.

Reaction time in healthy elderly is associated with chronic low-grade inflammation and advanced glycation end product.

Chronic inflammation and Advanced Glycation End products (AGE) are associated with sarcopenia. Decreased voluntary muscle activation and increased antagonist coactivation can contribute to age-related muscle weakness. The influence of chronic inflammation and AGE in these neuromuscular mechanisms is not clear. We studied whether a relation exists between circulating levels of inflammatory cytokines and AGEs as well as the interplay between agonist and antagonist muscle activation. We studied 64 community-dwelling old subjects, during a maximal isometric voluntary contraction (MVC) and a reaction-time (RT) test of the upper limb. Twenty-five circulating inflammatory biomarkers were determined. Linear regression showed significant relationships between chronic inflammation and six muscle activation parameters. MIP-1ß showed a significant negative relation with antagonist coactivation (during MVC) and antagonist muscle activity during pre-movement time (PMT) and movement time (MT) (during RT). A higher level of pentosidine (AGE) was predictive for a longer PMT. We conclude that in older relatively healthy persons antagonist muscle activation is influenced by chronic inflammation, contributing to age-related muscle weakness. Our results also suggest a mechanical and inflammatory influence of pentosidine in upper limb slowing of movement. These findings show novel insight in underlying mechanisms of age-related muscle weakness.

Peripheral muscle fatigue in hospitalised geriatric patients is associated with circulating markers of inflammation.

Geriatric patients with acute infection show increased muscle weakness and fatigability but the relative contribution of central and peripheral factors is unclear. Hospitalised patients with acute infection (82±6years, N=10) and community-dwelling controls (76±6years, N=19) sustained a maximal voluntary isometric contraction of the M. Adductor Pollicis until strength dropped to 50% of its maximal value. Voluntary muscle activation (VA) was assessed before and at the end of the fatigue protocol using twitch interpolation method and muscle activity was monitored using surface electromyography. Twenty-five circulating inflammatory biomarkers were determined. At pre-fatigue, no significant difference in VA was found between groups. VA decreased to similar levels (~50%) at the end of the fatigue protocol with no association with inflammatory biomarkers. In geriatric patients, muscle activity decreased significantly (p<0.05) during the fatigue protocol, whereas it increased in the controls (time∗group interaction p<0.05). The decrease in muscle activity was significantly related to higher levels of inflammation. Although slower muscle contraction and relaxation were significantly related to higher levels of inflammation, no statistical differences were found between groups. Our results confirm that muscle activity is significantly altered in older patients with acute infection and that local processes are involved.

Age-related differences in muscle recruitment and reaction-time performance.

Previously, we showed that prolonged reaction-time (RT) in older persons is related to increased antagonist muscle co-activation, occurring already before movement onset. Here, we studied whether a difference in temporal agonist and antagonist muscle activation exists between young and older persons during an RT-test. We studied Mm. Biceps (antagonist muscle) & Triceps (agonist muscle) Brachii activation time by sEMG in 60 young (26 ± 3 years) and 64 older (80 ± 6 years) community-dwelling subjects during a simple point-to-point RT-test (moving a finger using standardized elbow-extension from one pushbutton to another following a visual stimulus). RT was divided in pre-movement-time (PMT, time for stimulus processing) and movement-time (MT, time for motor response completion). Muscle activation time 1) following stimulus onset (PMAT) and 2) before movement onset (MAT) was calculated. PMAT for both muscles was significantly longer for the older subjects compared to the young (258 ± 53 ms versus 224 ± 37 ms, p=0.042 for Biceps and 280 ± 70 ms versus 218 ± 43 ms for Triceps, p<0.01). Longer agonist muscle PMAT was significantly related to worse PMT and RT in young (respectively r=0.76 & r=0.68, p<0.001) and elderly (respectively r=0.42 & r=0.40, p=0.001). In the older subjects we also found that the antagonist muscle activated significantly earlier than the agonist muscle (-22 ± 55 ms, p=0.003). We conclude that in older persons, besides the previously reported increased antagonist muscle co-activation, the muscle firing sequence is also profoundly altered. This is characterized by a delayed muscle activation following stimulus onset, and a significantly earlier recruitment of the antagonist muscle before movement onset.

The influence of strength training on muscle activation in elderly persons: a systematic review and meta-analysis.

Age-related muscle weakness is only partially related to muscle atrophy, due to neuromuscular changes including reduced voluntary muscle activation and antagonist muscle co-activation. The respective contribution of these mechanisms in exercise-induced strength gains at higher age is unclear. Here the literature was systematically reviewed for studies reporting exercise-induced effects on voluntary muscle activation and antagonist muscle co-activation in elderly persons. Seventeen relevant studies were identified, 4 investigated voluntary muscle activation, 8 antagonist muscle co-activation and 5 studies investigated both. Meta-analysis showed an exercise-induced improvement in voluntary activation in plantar flexors (weighted mean difference (WMD) +8.8%, p<0.001), and knee extensors (WMD +1.8%, p<0.001), with greater gains in activation capacity obtained in subjects with lower voluntary activation level prior to the onset of training. We found no significant overall effect of strength training on antagonist co-activation during ankle plantar flexion (WMD +0.6%, p=0.686) or knee extension (WMD -1.1%, p=0.699 for the RCT's and -1.8%, p=0.516 for the non-controlled trials). Based on our results we can conclude that there is evidence for exercise-induced increase in voluntary activation related to strength gains in the lower extremities in elderly persons. The results for exercise-induced effects on antagonist co-activation are inconsistent and more research is necessary to determine its contribution to strength gains following resistance training in elderly persons.

Coping with stress: a survey of Murdoch University veterinary students.

Students in veterinary schools can experience stress in balancing the different demands on them-academic, interpersonal, intrapersonal, and professional or work related-as well as managing potential conflict between animal and human interests. Practicing veterinarians report many similar stressors and reactions. Stressful stimuli produce stress reactions that can be inimical to physical and psychological well-being, and students' performance in veterinary programs can be adversely affected if they do not have coping resources. While there has been some research into stress among university students in general, and among medical students in particular, there is little on the experience of veterinary students. This article describes a study by the School of Psychology, commissioned by the Department of Veterinary Clinical Sciences, at Murdoch University in Western Australia. It was designed to investigate the levels and causes of stress among, and the frequency and type of coping strategies used by, fourth- and fifth-year students. Results indicate that the students in this cohort faced frequent stressors and felt at least moderately stressed but did not routinely and systematically use a range of coping strategies. Academic stressors and perceived responsibilities attached to moving into practical or professional areas figured strongly and were associated with higher levels of stress in the students, in particular physical sequelae. Though the numbers were small, it is of concern that some students were using measures that were potentially harmful. Some recommendations are made here about measures that veterinary programs may be able to incorporate to address stress in their students. Information is included on current strategies within the curriculum to manage potential stressful situations as part of students' professional development.