Biomedical subjects

Kristina M Calder

Publications and source records attributed to Kristina M Calder.

3 recordsLinked to original sources

PubMed2006

Physiological characteristics of motor units in the brachioradialis muscle across fatiguing low-level isometric contractions.

The purpose of this study was to determine (i) if decomposition-based quantitative electromyography (DQEMG) could detect changes in motor unit potential (MUP) morphology and motor unit (MU) firing pattern statistics associated with muscle fatigue, (ii) if any detected changes are correlated with surface electromyographic (SEMG) signs of fatigue, and (iii) if significant fatigue-dependent changes are repeatable within individuals. Mean MU firing rates and the morphology of MUPs detected using needle and surface electrodes during constant-torque isometric contractions held until exhaustion were investigated in the brachioradialis (BR) muscle in 10 healthy volunteers (mean age=28.6 yr, SD+/-3.9). Time dependant changes were investigated using an analysis of variance with normalized time as a main effect. Partial correlation coefficients were computed using a repeated measures analysis of covariance to determine if changes in MU firing rates, needle-detected MUPs and surface-detected MUPs (SMUPs) were related to changes in SEMG signal amplitude and frequency parameters. Intraclass correlation coefficients (ICCs) were used to determine the within-subject repeatability of changes in MU firing rates, and MUP and SMUP parameters. Significant decreases in mean MU firing rates were found along with significant increases in various duration and area related parameters in both MUPs and SMUPs across the fatiguing contraction. The SEMG signal demonstrated the expected changes with fatigue: an increase in amplitude and a decrease in frequency content. SEMG amplitude was significantly positively correlated with SMUP peak-to-peak voltage (r=0.85, p<0.05), and SMUP area (r=0.86, p<0.05). Mean power frequency was significantly negatively correlated with SMUP negative peak duration (r=-0.74, p<0.05). The significant time-dependent changes were reliably observed (ICCs were 0.94 for MUP peak to peak amplitude, 0.97 for MUP area and 0.95 for MUP area to amplitude ratio, 0.95 for SMUP peak-to-peak voltage, 0.83 for SMUP area, 0.99 for SMUP negative peak amplitude and 0.88 for SMUP negative peak area). The decreases in mean MU firing rates measured along with the increases in amplitude, duration and area parameters of MUPs and SMUPs and their partial correlation with SEMG amplitude during submaximal fatiguing contractions of the BR, suggest that recruitment is a main cause of increased SEMG amplitude parameters with fatigue. We conclude that DQEMG can be effectively and reliably used to detect changes in physiological characteristics of MUs that accompany fatigue.

Adult↗

PubMed2006

Adaptations during familiarization to resistive exercise.

This study focused on adaptations during familiarization to resistive exercise. It was also determined if familiarization requires one or more sessions. Twenty-six sedentary, college-aged females were matched and randomly assigned to one of two groups. Measurements were obtained during the initial familiarization period (Group 1: 15 trials on 1 day, Group 2: 5 trials on each of three consecutive days), and during retention tests scheduled two weeks and 3 months after the first test session. Elbow flexion torque and surface electromyography (SEMG) of the biceps and triceps were monitored concurrently. There were no significant differences between groups for any of the criterion measures. There was a significant (p<0.05) increase (12.4 Nm, or 38.8%) in maximal isometric elbow flexion torque. Biceps (agonist) root-mean-square (RMS) SEMG exhibited a significant (p<0.05) increase of 95 microV (29%). Triceps (antagonist) RMS SEMG underwent alternating decreases then increases, and each change was significant (p<0.05). The ratio of biceps to triceps RMS SEMG was used to assess cocontraction, and it followed the same pattern of change as triceps RMS SEMG. We concluded that both groups responded in the same way to testing, regardless of the pattern of the first 15 contractions. The increase in maximal isometric elbow flexion torque was due to neural drive to the bicep (agonist). There was a low level of triceps (antagonist) cocontraction to provide joint stability, and it was adjusted throughout the duration of testing.

Adaptation, Physiological↗

PubMed2005

Reliability of the biceps brachii M-wave.

BACKGROUND: The peak-to-peak (P-P) amplitude of the maximum M-wave and the area of the negative phase of the curve are important measures that serve as methodological controls in H-reflex studies, motor unit number estimation (MUNE) procedures, and normalization factors for voluntary electromyographic (EMG) activity. These methodologies assume, with little evidence, that M-wave variability is minimal. This study therefore examined the intraclass reliability of these measures for the biceps brachii. METHODS: Twenty-two healthy adults (4 males and 18 females) participated in 5 separate days of electrical stimulation of the musculocutaneous nerve supplying the biceps brachii muscle. A total of 10 stimulations were recorded on each of the 5 test sessions: a total of fifty trials were used for analysis. A two-factor repeated measures analysis of variance (ANOVA) evaluated the stability of the group means across test sessions. The consistency of scores within individuals was determined by calculating the intraclass correlation coefficient (ICC). The variance ratio (VR) was then used to assess the reproducibility of the shape of the maximum M-wave within individual subjects. RESULTS: The P-P amplitude means ranged from 12.62 +/- 4.33 mV to 13.45 +/- 4.07 mV across test sessions. The group means were highly stable. ICC analysis also revealed that the scores were very consistent (ICC = 0.98). The group means for the area of the negative phase of the maximum M-wave were also stable (117 to 126 mV.ms). The ICC analysis also indicated a high degree of consistency (ICC = 0.96). The VR for the sample was 0.244 +/- 0.169, which suggests that the biceps brachii maximum M-wave shape was in general very reproducible for each subject. CONCLUSION: The results support the use of P-P amplitude of the maximum M-wave as a methodological control in H-reflex studies, and as a normalization factor for voluntary EMG. The area of the negative phase of the maximum M-wave is both stable and consistent, and the shape of the entire waveform is highly reproducible and may be used for MUNE procedures.

Journal Article↗