Abstract
The term “bilateral deficit” (BLD) has been used to describe a reduction in performance during bilateral contractions when compared to the sum of identical unilateral contractions. In old age, maximal isometric force production (MIF) decreases and BLD increases indicating the need for training interventions to mitigate this impact in seniors. In a cross-sectional approach, we examined age-related differences in MIF and BLD in young (age: 20–30 years) and old adults (age: >65 years). In addition, a randomized-controlled trial was conducted to investigate training-specific effects of resistance vs. balance training on MIF and BLD of the leg extensors in old adults. Subjects were randomly assigned to resistance training (n = 19), balance training (n = 14), or a control group (n = 20). Bilateral heavy-resistance training for the lower extremities was performed for 13 weeks (3 × / week) at 80% of the one repetition maximum. Balance training was conducted using predominately unilateral exercises on wobble boards, soft mats, and uneven surfaces for the same duration. Pre- and post-tests included uni- and bilateral measurements of maximal isometric leg extension force. At baseline, young subjects outperformed older adults in uni- and bilateral MIF (all p < .001; d = 2.61–3.37) and in measures of BLD (p < .001; d = 2.04). We also found significant increases in uni- and bilateral MIF after resistance training (all p < .001, d = 1.8-5.7) and balance training (all p < .05, d = 1.3-3.2). In addition, BLD decreased following resistance (p < .001, d = 3.4) and balance training (p < .001, d = 2.6). It can be concluded that both training regimens resulted in increased MIF and decreased BLD of the leg extensors (HRT-group more than BAL-group), almost reaching the levels of young adults.
Highlights
Bilateral deficit (BLD) is a well-known neurophysiological phenomenon characterized by a reduction in force generating capacity during synchronous bilateral contractions when comparedPLOS ONE | DOI:10.1371/journal.pone.0118535 February 19, 2015Training Effects on BLD in Old Age to the sum of identical unilateral contractions [1,2,3,4]
Attendance rates amounted to 89% for the heavyresistance strength training (HRT)-group and 91% for the balance training (BAL)-group
This is in accordance with our first hypothesis; (2) both older intervention groups significantly improved their uni- and bilateral maximal isometric force production (MIF) as well as their BLD (HRT-group more than BAL-group); (3) following training, uni- and bilateral MIF and BLD of old adults approximated those of young adults
Summary
Bilateral deficit (BLD) is a well-known neurophysiological phenomenon characterized by a reduction in force generating capacity during synchronous bilateral contractions when comparedPLOS ONE | DOI:10.1371/journal.pone.0118535 February 19, 2015Training Effects on BLD in Old Age to the sum of identical unilateral contractions [1,2,3,4]. Bilateral deficit (BLD) is a well-known neurophysiological phenomenon characterized by a reduction in force generating capacity during synchronous bilateral contractions when compared. Cortical inhibition decreases neural drive to the activated muscles during bilateral contractions, thereby resulting in force decrements [10,13]. In this context, BLD reflects a neural inhibitory mechanism during symmetrical bilateral muscle contractions [4,11]. BLD reflects a neural inhibitory mechanism during symmetrical bilateral muscle contractions [4,11] It can be assessed as a proxy for the role of central activation during force generation
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