Biomedical subjects

Juha Oksa

Publications and source records attributed to Juha Oksa.

9 recordsLinked to original sources

PubMed2006

Changes in neuromuscular function due to intermittently increased workload during repetitive work in cold conditions.

OBJECTIVES: This study attempted to determine whether repetitive work in the cold affects the number of electromyographic (EMG) gaps and whether cold-induced deterioration in neuromuscular function can be restored by altering work intensity. METHODS: During 2 hours of simulated sausage packing, the occurrence of EMG gaps was studied in eight upper-extremity muscles at 19 degrees C and 4 degrees C. The additional effect of continuous, light repetitive work [wrist flexion-extension 10% of the maximal voluntary contraction (MVC), Cwork] and intermittently increased workload (10% or 30% MVC) (Iwork) on forearm muscle EMG gaps, the median frequency of the EMG spectrum, EMG activity, and muscle fatigue (as indicated by changes in the MVC of wrist flexion) at 4 degrees C was studied. RESULTS: During work simulation, the mean skin temperature decreased from 33.3 (SD 0.1) degrees C to 30.6 (SD 0.2) degrees C (P<0.05), and the number of EMG gaps diminished in seven muscles by 1.4-68.2% (P<0.05). During Iwork there were 44% and 37% more EMG gaps in the forearm flexors and extensors, respectively, and the median frequency shifted to higher frequencies (P<0.05) as compared with the situation in Cwork. The average EMG activity of the forearm flexors was 13% lower (P<0.05) during Iwork than during Cwork. Wrist flexion MVC decreased 18% and 15% in Cwork and Iwork, respectively. CONCLUSIONS: The cold-induced decrease in the number of EMG gaps and increased muscle strain and fatigue can be, at least partially, restored by intermittently increasing the workload (ie, breaking the monotonous work cycle).

Adult↗

PubMed2006

The effect of training of military skills on performance in cold environment.

This study was conducted to evaluate how training for disassembling and assembling a weapon and patrol data message terminal and loading a magazine in different temperatures affected the ability to perform those skills in a cold environment. One group trained six times on separate days in a warm environment (19 degrees C), the second group trained three times in a warm environment and then three times in a cold environment (-15 degrees C), and the third group trained six times in the cold environment. Training first in warm and then in cold shortened performance time by 6% to 28%, in comparison to training only in a warm environment. Also, training in cold made the subjects faster than training in warm. In conclusion, before performing military operations in a cold environment, it is most beneficial to train first in warm and then in cold. Training only in warm produces the lowest level of performance in a cold environment.

Adaptation, Physiological↗

PubMed2006

Trampoline exercise vs. strength training to reduce neck strain in fighter pilots.

INTRODUCTION: Fighter pilots' muscular strength and endurance are subjected to very high demands. Pilots' fatigued muscles are at higher risk for injuries. The purpose of this study was to compare the effects of two different training methods in reducing muscular loading during in-flight and cervical loading testing (CLT). METHODS: There were 16 volunteer Finnish Air Force cadets who were divided into 2 groups: a strength training group (STG) and a trampoline training group (TTG). During the 6-wk training period, the STG performed dynamic flexion and extension and isometric rotation exercises, and the TTG performed trampoline bouncing exercises. During in-flight and CLT, muscle strain from the sternocleidomastoid, cervical erector spinae, trapezius, and thoracic erector spinae muscles was recorded with EMG. RESULTS: In-flight muscle strain in the STG after the training period decreased in the sternocleidomastoid 50%, cervical erector spinae 3%, trapezius 4%, and thoracic erector spinae 8%. In the TTG, the decrease was 41%, 30%, 20%, and 6%, respectively. In CLT, the results were similar. After a 3-mo follow-up period with intensive high +Gz flying, EMG during CLT was still lower than in baseline measurements. CONCLUSION: Both training methods were found to be effective in reducing muscle strain during in-flight and CLT, especially in the cervical muscles. There was no statistically significant difference between the training groups. Introduced exercises expand muscles' capacities in different ways and the authors recommend both strength and trampoline training programs to be included in fighter pilots' physical education programs.

Adult↗

PubMed2005

Postural sway during single and repeated cold exposures.

INTRODUCTION: Tissue cooling changes sensory and neuromuscular functions that are also involved in postural control. The purpose of the study was to determine how acute and repeated exposures to cold affect whole body postural control. METHODS: Postural sway was measured from 10 subjects during standing with eyes open (EO) and closed (EC) using an inclinometer-based method. Sway was assessed at at 10 degrees C on 10 consecutive days and at 25 degrees C on days 1, 5, and 10. Sway path length, area, velocity, side-to-side and forward-backward movement were assessed. At the same time, rectal and skin temperatures, muscle tonus/ shivering, thermal sensations, and comfort were recorded. RESULTS: Acute exposure to 10 degrees C caused thermal discomfort, significantly lowered (26.1-26.5 degrees C) mean skin temperatures, slightly lowered rectal temperature (36.7 degrees C) and increased (140-260%) muscle tone, increased sway path length (67-87%, p < 0.05), velocity (63-71%, p < 0.05), total sway area (42-67%, p < 0.05), and forward-backward movement (35-57%, p < 0.05) compared with 25 degrees C. Side-to-side movements were not altered in the cold. Postural sway increased with EC, and further when exposed to cold, but the effect of cold was smaller compared with EO. Repeated exposures over the 10-d period decreased sway 10-40% both at 25 degrees C and at 10 degrees C (p < 0.05-0.01), suggesting motor learning. The difference in sway between 25 degrees C and 10 micro C remained the same throughout the 10-d period, suggesting that the observed cold habituation responses do not affect sway. CONCLUSIONS: The results demonstrate that postural control is impaired in cold, which may affect physical performance in cold environmental conditions.

Adult↗

PubMed2004

Thermal sensation and comfort in women exposed repeatedly to whole-body cryotherapy and winter swimming in ice-cold water.

Whole-body cryotherapy (WBC; -110 degrees C) and winter swimming (WS) in ice-cold water are severe ambient cold exposures, which are voluntarily practiced by humans in minimal clothing. The purpose was to examine thermal sensation and thermal comfort associated with WBC and WS. Twenty women similar in body mass index, age, physical activity, and use of hormonal contraception were pairwise randomized either to the WBC group or the WS group. The duration of each WBC exposure was 2 min, which was repeated three times per week for 3 months (13 weeks). Similar exposure frequency was used for the WS group, but each exposure lasted 20 s in outdoor conditions. Thermal sensation and comfort were asked with standard scales. After WBC, 65% of the thermal sensation votes were 'neutral' or 'slightly cool.' After WS, 81% of the thermal sensation votes were 'warm,' 'neutral,' or 'slightly cool.' Majority of comfort votes immediately after exposures in WBC group (98%) and in the WS group (93%) were 'comfortable' or 'slightly uncomfortable.' Thermal sensation and comfort became habituated in both groups at an early stage of trials, but the changes were less conclusive in WS group due to variable conditions outdoors. In the WBC group, cold sensation was less intense already after the second exposure. In conclusion, repeated exposures to WBC and WS in healthy women were mostly well tolerated and comfortable. The results indicate that during repeated severe whole-body cold stress of short duration, thermal sensation and comfort become habituated during the first exposures.

Adult↗

PubMed2003

Force control of isometric elbow flexion with visual feedback in cold with and without shivering.

BACKGROUND: Exposure to cold impairs manual performance through effects on muscle tissue and control mechanisms. The purpose of this study was to assess the influence of increased muscle tone and shivering on ability to maintain required force during isometric flexion over a wide range of effort levels. METHODS: Lightly clad male subjects (n = 6) were exposed to thermoneutral air (TN, 27 degrees C) for 30 min, or to cold air (CA, 10 degrees C) for 30 min followed by a cold drink (1 L, 8 degrees C) to cause vigorous shivering (SH). At the end of each condition, subjects performed isometric elbow flexion at 10, 20, 40, and 80% of individual maximal voluntary contraction (MVC) for 10 s each, using digital visual feedback to control the force. We analyzed mean force output (F), the coefficient of force variation (FCv), information transmission (F/SD), and the coefficient of force auto-correlation (Ra), and the averaged electromyogram (aEMG) from elbow flexors, elbow extensor, and pectoral girdle muscles. RESULTS: Compared with TN, CA with increased muscle tone raised the aEMG by 5-30% but did not impair any of the force characteristics. In SH, F was not affected, while FCv and Ra were significantly increased at 10% MVC, while aEMG increased by 30-400% depending on the specific muscle and MVC level. CONCLUSION: Neither thermoregulatory muscle tone nor shivering influenced the control of force output during isometric elbow flexion, except that at the lowest MVC (10%) the force output was more variable during shivering.

Adult↗

PubMed2003

The effect of lumbar support on the effectiveness of anti-G straining manuevers.

INTRODUCTION: The ability of fighter pilots to perform efficient anti-G straining maneuvers (AGSM) is vital for their G-tolerance. The aim of this study was to evaluate if the use of a lumbar support that optimizes the posture of the spine enhances the effectiveness of AGSM. METHODS: Eleven fighter pilots performed four AGSM training sessions with 4-5 repetitions in each session, each lasting approximately 10 s. The sessions were done without lumbar support or using supports that were 7, 14, or 26 mm thick. During the sessions, the electromyogram (EMG) data were recorded from eight muscles (rectus and biceps femoris, gluteus maximus, erector spinae, rectus abdominis, obliquus externus, latissimus dorsi, and pectoralis major). RESULTS: In a single best AGSM, average EMG (aEMG) increased 12%, 10%, and 14% and power spectrum area (PSA) increased 20%, 26%, and 44% while using 7-, 14-, and 26-mm supports, respectively, in relation to the condition without support. According to aEMG and PSA, effectiveness increased in 11 and 10 subjects, respectively, with the average increase being 12% (aEMG) and 25% (PSA). During the whole session (repeated AGSM), effectiveness was best with support in 7 subjects and without support in 4 subjects. In the total population, the average increase in the effectiveness during repeated AGSM was 6% and 11% with aEMG and PSA, respectively. DISCUSSION: The use of lumbar support tended to increase the effectiveness of muscular work, especially during single AGSM, but also during repeated AGSM.

Adult↗

PubMed2002

Combined effect of repetitive work and cold on muscle function and fatigue.

This study compared the effect of repetitive work in thermoneutral and cold conditions on forearm muscle electromyogram (EMG) and fatigue. We hypothesize that cold and repetitive work together cause higher EMG activity and fatigue than repetitive work only, thus creating a higher risk for overuse injuries. Eight men performed six 20-min work bouts at 25 degrees C (W-25) and at 5 degrees C while exposed to systemic (C-5) and local cooling (LC-5). The work was wrist flexion-extension exercise at 10% maximal voluntary contraction. The EMG activity of the forearm flexors and extensors was higher during C-5 (31 and 30%, respectively) and LC-5 (25 and 28%, respectively) than during W-25 (P < 0.05). On the basis of fatigue index (calculated from changes in maximal flexor force and flexor EMG activity), the fatigue in the forearm flexors at the end of W-25 was 15%. The corresponding values at the end of C-5 and LC-5 were 37% (P < 0.05 in relation to W-25) and 20%, respectively. Thus repetitive work in the cold causes higher EMG activity and fatigue than repetitive work in thermoneutral conditions.

Adult↗

PubMed2002

Neuromuscular performance limitations in cold.

This review will focus on the effects of cooling on muscular performance and its variables, functional properties of the muscles and some neural aspects of muscle function. The changes are described in terms of different cold exposures with varying intensity, therefore also looking at the dose dependent relationship between cooling and performance decrement. In addition, relationship between rewarming exercise and performance enhancement is described. Future research needs are addressed.

Biomechanical Phenomena↗