HRV measurements are beneficial in exercise training prescription in moderately active men and women. Women benefit from HRV guidance by achieving significant improvement in fitness with a lower training load.

The purpose of this study is to evaluate whether the use of an activity monitor providing feedback has an effect on physical activity (PA) in young men. A population-based sample of 276 conscription-aged (mean = 17.9, SD = 0.7 years) men participated in a 3-month randomized controlled trial in Oulu in 2012. Participants were randomized to an intervention group (INT, N = 137) and a control group (CON, N = 139). INT received a wrist-worn monitor (Polar Active) showing daily activity, and CON received identical monitors without feedback. Main outcome was the change from baseline in objectively measured weekly time spent in moderate-to-vigorous PA (MVPA) and sedentary activity (SED), as assessed by generalized estimation equations (GEE). Other lifestyle factors were assessed by a questionnaire at baseline and at 3 months. Weekly physical activity data (≥ 4 days with ≥ 8 h each) were obtained from 72 (53%) and 90 (65%) men in the INT and CON, respectively. Based on GEE, time spent in MVPA increased (p = 0.012) and SED decreased (p = 0.032) in the INT compared with the CON. During the first 7 weeks, the INT spent on average 1 h less sedentary than the CON (t-test, p < 0.05). During the first week, the INT showed 12 minutes more MVPA compared to the CON (t-test, p = 0.034). Based on questionnaire data, the proportion of the most sedentary men decreased in the INT (Wilcoxon test, 28% vs. 10%, p = 0.029), with no change in the CON (20% vs. 19%, p = 0.546). To conclude, a wrist-worn activity monitor providing feedback had a short-term positive effect on PA and SED in young men.Trial registrationThis is a pilot study for a larger randomized controlled trial registered to the clinical trials register NCT01376986.

Heart rate is a useful indicator of physiological adaptation and intensity of eþ ort. Therefore, heart rate m onitoring is an important component of cardiovascular ® tness assessm ent and training programmes. The electrocardiogram (ECG) and Holter monitoring devices are accurate, but they are not appropriate for use in ® eld settings due to cost, size and complexity of operation. Lightweight telemetric heart rate monitors equipped with conventional electrodes have been available since 1983 and have been shown to be accurate and valid tools for heart rate m onitoring and registering in the ® eld. Polar Electro Oy has been at the forefront of ambulatory heart rate monitor technology for 15 years. This paper reviews the development of Polar heart rate m onitors and their measurement accuracy compared to Holter ECG devices at rest and during exercise, both in adults and in children.

Immobilization has been shown to cause muscle atrophy and decreased total collagen synthesis in skeletal muscle. These changes can be counteracted by stretch. The purpose of this study was to find out the early effects of immobilization in shortened and lengthened positions on expression of type I and III collagen at pre- and post-translational level. The mRNA levels of type I and III collagen, prolyl 4-hydroxylase activity, total collagen concentration and the proportions of type I and III collagens were analysed in soleus (SOL), gastrocnemius (GM), extensor digitorum longus and tibialis anterior (TA) muscles during immobilization in shortened and lengthened positions for 1, 3 and 7 days. The mRNA levels for type I and III collagens decreased during 3-7 days in all muscles, except TA. In shortened GM and SOL, the mRNA level of type I collagen was lower than in the corresponding lengthened muscles. Prolyl 4-hydroxylase activity decreased in all muscles during 3-7 days. The activity in shortened GM was 30-37% lower than in the lengthened one during 3-7 days. Total collagen concentration and proportions of type I and III collagen showed no change during the 7-day immobilization period. The present study suggests that immobilization results in rapid down-regulation of total muscular collagen synthesis and that the timing and degree is roughly similar in type I and III collagens. Stretch seems to partially counteract these effects. Immobilization effect and the partially preventive effect of stretch on down-regulation of gene expression of prolyl 4-hydroxylase and fibrillar collagens during immobilization seems to be greater in weight-bearing SOL and GM than ankle joint dorsiflexors.

Collagen plays an important role in skeletal muscle both during muscle differentiation and normal muscle growth, and also serves a role as a supportive structure. It is the most abundant protein of the extracellular matrix and of the 19 distinct collagen types, types I, III, IV and V are the dominating ones in skeletal muscle. Both collagen synthesis as well as degradation is influenced by either physical loading or immobilization in skeletal muscle, and recent methods have allowed for greater understanding of the posttranslational processing of collagen.