Oestrogen status in relation to the early training responses in human thumb adductor muscles

• Published in: Acta Physiologica Vol. 188; no. 1; pp. 41 - 52
• Main Authors: Onambele, G. N. L., Bruce, S. A., Woledge, R. C.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.09.2006; Blackwell
• Subjects: adductor pollicis; Adult; Analysis of Variance; Biological and medical sciences; Contraceptives, Oral, Hormonal; Electromyography - instrumentation; Electromyography - methods; Estrogen Replacement Therapy; Estrogens - physiology; Female; first dorsal interoseus; Functional Laterality; Fundamental and applied biological sciences. Psychology; Humans; Isometric Contraction; isometric force; Linear Models; Middle Aged; Muscle Contraction - physiology; muscle cross-sectional area; Muscle Fibers, Fast-Twitch - physiology; Muscle, Skeletal - anatomy & histology; Muscle, Skeletal - physiology; oestrogen; Physical Education and Training; stretch force; Thumb; training; twitch interpolation; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Human; oestrogen; muscle cross-sectional area; Adductor pollicis muscle; Force; twitch interpolation; Thumb; Finger; Estrogen; first dorsal interoseus; stretch force; training; Striated muscle; Dorsal interosseous muscle; Ovarian hormone; Motor unit; Recruitment; Interpolation; Dragging; Female; Sex steroid hormone; adductor pollicis; isometric force
• ISSN: 1748-1708; 1748-1716
• DOI: 10.1111/j.1748-1716.2006.01597.x

Aims:  The aims of this study were to identify the mechanisms for the early response to training in women of different oestrogen status and to determine whether any oestrogen and exercise effects on these would be additive. Methods:  We monitored training (ten 5‐s contractions per day for 12 weeks)‐induced changes in the size, strength, voluntary activation capacity and index of crossbridge force state (i.e. rapid stretch to isometric torque ratio), in the thumb adductor muscles of postmenopausal [eight who had never used, and 14 who were using, hormone replacement therapy (HRT)] and seven premenopausal eumenorrhoeic women. The contralateral untrained muscle was used as a control. Results:  There was a significant effect of oestrogen status on the magnitude of training‐induced strength increment, with the non‐HRT postmenopausal group exhibiting the greatest benefits (28 ± 6%, P = 0.024) from training. There were no significant or commensurate changes in either cross‐sectional area or voluntary activation capacity. The index of crossbridge force state improved most in the no‐HRT group (19 ± 7%, P < 0.05). Conclusions:  Presence, rather than absence of oestrogen, is associated with relatively higher muscle function which limits the potential for any further training‐induced increments in muscle performance, as would be expected if the muscle strengthening actions of training and oestrogen share a common, partially saturable physiological pathway. The mechanism that is involved in the early training‐induced strength increment in the three differing oestrogen groups cannot be due to increased size or recruitment. It would appear instead that increased motor unit firing frequency is involved.